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Anastomosis: An opening created by surgical, traumatic, or pathological means between 2 normally separate spaces or organs.
Aneurysm: An abnormal blood-filled dilation of a blood vessel wall (most commonly in arteries) resulting from disease of the vessel wall.
Pseudoaneurysm: A vascular abnormality that resembles an aneurysm, but the outpouching is not limited by a true vessel wall, rather by external fibrous tissue.
Angioplasty: The repair of a blood vessel abnormality.
Percutaneous transluminal angioplasty: The repair of a lesion using an endoluminal approach, usually with a balloon that can be inflated to pressures up to 30 atmospheres.
Antibiotic lock: Instillation of an antibiotic solution into the lumen of a dialysis catheter for the entire interdialytic period; antibiotics tested include vancomycin, aminoglycosides, and minocycline.
Antimicrobial lock: Instillation of an antimicrobial solution into the lumen of a dialysis catheter for the entire interdialytic period; antimicrobial solutions include high-concentration citrate, high-concentration EDTA, and taurolidine.
Antimicrobial: Any agent capable of destroying or inhibiting the growth of microorganisms.
Antiseptic: Any agent capable of preventing infection by inhibiting the growth of microorganisms.
Cannulation: The insertion of cannulae (by definition, a needle with a lumen) or angiocaths into a vascular vessel.
Buttonhole technique or constant-site technique: The repeated cannulation into the exact same puncture site so that a scar tissue tunnel track develops. The scar tissue tunnel track allows the needle to pass through to the outflow vessel of the fistula following the same path with each cannulation time. Only used in fistulae. Should not be used for accessing grafts.
Catheter: A device providing access to the central veins or right atrium, permitting high-volume flow rates.
Exit site: The location on the skin that the catheter exits through the skin surface.
Insertion site: Location at which the catheter enters the vein, for example, the right internal jugular vein is the preferred insertion site.
Long-term catheter: Also known as tunneled cuffed catheter (TCC); a device intended for use for longer than 1 week that typically is tunneled and has a cuff to promote fibrous ingrowth to prevent catheter migration and accidental withdrawal.
Port catheter system: Subcutaneous device for hemodialysis access that is cannulated with needles; the device contains a ball-valve system that is connected to 1 or more central venous catheters (CVCs).
Short-term catheter: A device intended for short-term use (<1 week) that typically is not tunneled. Intended for use in hospitalized patients; not for outpatient maintenance dialysis.
Diagnostic testing: Specialized testing that is prompted by some abnormality or other medical indication and that is undertaken to diagnose the cause of the vascular access dysfunction.
Dialysance: The number of milliliters of blood completely cleared of any substance by an artificial kidney or by peritoneal dialysis in a unit of time, usually a minute, with a specified concentration gradient.
Distal revascularization—interval ligation (DRIL): A surgical procedure to reduce ischemia to the hand caused by steal syndrome.
Elastic recoil: The recurrence of stenosis following angioplasty.
Fistula (plural, fistulae): Autogenous autologous arteriovenous fistula, also referred to as native.
Brescia-Cimino (radiocephalic) fistula: An autologous fistula constructed between the radial artery and the cephalic vein at the wrist.
Gracz fistula: An autologous fistula constructed between the brachial artery and a branch of the medial antecubital vein, the perforating vein, below the elbow.
Snuff-box fistula: An autologous fistula constructed between a branch of the radial artery and an adjacent vein in the anatomic snuff box of the hand.
Fistula maturation: The process by which a fistula becomes suitable for cannulation.
Rule of 6s: A fistula in general must be a minimum of 6 mm in diameter with discernable margins when a tourniquet is in place, less than 6 mm deep, have a blood flow greater than 600 mL/min, and should be evaluated for nonmaturation if, after 6 weeks from surgical creation, it does not meet these criteria.
Flow: The amount of blood flowing through a system.
QA: Access blood flow.
Qf: Ultrafiltration rate.
QB: Blood pump flow delivered to the dialyzer.
Flow measurement methods:
Crit line: Using changes in hematocrit (Hct) induced by ultrafiltration.
GPT: Glucose pump (infusion) technique.
HDM: Hemodialysis monitor using magnetic detection of differential conductivity.
Ionic dialysance: A method that uses a change in dialysis fluid sodium concentration to calculate flow.
TQA: Direct transcutaneous optodilutional flow method.
UDT: Ultrasound dilution technique.
VFDU: Variable flow Doppler ultrasound.
Graft: A conduit of synthetic or biological material connecting artery to vein.
Synthetic: Made of plastic polymers, such as polytetrafluoroethylene (PTFE), polyurethane (PU).
Biological: Made of biological materials, such as bovine carotid artery, cryopreserved human femoral veins, etc.
Tapered: Grafts for which internal diameter varies from the arterial to the venous end.
Untapered: Grafts with a uniform diameter, usually 6 mm.
Kt/V: A dimensionless quantity that assesses the amount of dialysis delivered.
Monitoring: The evaluation of the vascular access by means of physical examination to detect physical signs that suggest the presence of dysfunction.
Magnetic resonance angiography (MRA): A technique to visualize the arterial and venous systems using gadolinium as the imaging agent.
Neointimal hyperplasia: The myoendothelial proliferation of cells and matrix that produces stenosis, primarily in grafts.
Online: The conductance of a test during a hemodialysis procedure.
Physical examination (of the access): Inspection, palpation, and auscultation of the access.
Pressure: Force applied uniformly over a surface, measured as force per unit of area; stress or force acting in any direction against resistance.
Mean arterial pressure (MAP): Usually recorded in the arm opposite the vascular access.
PIA: Pressure in the access when there is no external blood flow for dialysis, also referred to as the “static pressure.”
Venous drip chamber pressure (VDP): Also referred as dynamic venous pressure (DVP). Measured in the venous tubing and equal to the pressure required to infuse blood back into the vascular access at the blood pump flow set.
Recirculation: The return of dialyzed blood to the systemic circulation without full equilibration.
Cardiopulmonary recirculation: Resulting from the return of dialyzed blood without full equilibration with all systemic venous return.
Access recirculation: Resulting from the admixture of dialyzed blood with arterial access blood without equilibration with the systemic arterial circulation. Occurs under conditions in which blood pump flow is greater than access flow.
Receiver operating characteristic (ROC) curve: A technique to evaluate the sensitivity and specificity of a diagnostic test to detect/predict the presence of a disease state.
Steal syndrome: Signs and symptoms (pain, coldness, cyanosis, necrosis) produced by an access as a result of the diversion of arterial blood flow into the fistula.
Acronecrosis: Gangrene occurring in the distal part of the extremities, usually fingertips and toes.
Stenosis: A constriction or narrowing of a duct or passage; a stricture.
Cephalic arch stenosis: A common site for stenosis of the cephalic vein at an anatomic site where there is a narrowing of the cephalic vein as it arches over the shoulder in the region of the deltopectoral groove before the vein junction with the axillary vein.
Surveillance: The periodic evaluation of the vascular access by means of tests, which may involve special instrumentation and for which an abnormal test result suggests the presence of dysfunction.
Tissue plasminogen activator (tPA): A natural lytic used to dissolve fibrin or nonorganized thrombus.
Transposition: The movement of a vein from its normal position either by elevation to bring the vein closer to the skin or laterally to permit easier cannulation.
Ultrasound: The use of ultrasonic waves for diagnostic or therapeutic purposes, specifically to image an internal body structure.
Doppler ultrasound (DU): Ultrasound that uses the Doppler effect to measure movement or flow in the body and especially blood flow; also referred to as Doppler ultrasonography.
Duplex Doppler ultrasound (DDU): Combines Doppler and B-mode (grayscale) imaging to provide diagnostic ultrasound used for quantitative color velocity imaging, also referred to as Doppler sonography.
Systolic velocity ratio (SVR): The ratio of velocity in an abnormal vessel relative to a normal vessel.
Urokinase: A natural lytic used to dissolve fibrin or nonorganized thrombus.
Vascular access team (VAT): Patient and group of professionals involved in management of vascular access (includes caregivers who construct, cannulate, monitor, detect problems in, and repair vascular accesses). Caregivers include nephrologist, nephrology nurse, patient care technician, nurse practitioner, physician assistant, interventionalist, surgeons, and vascular access coordinator.
The publication of the second update of the Clinical Practice Guidelines (CPGs) and Clinical Practice Recommendations (CPRs) for Vascular Access represents the second update of these guidelines since the first guideline on this topic was published in 1997. The first set of guidelines established the importance of placing fistulae in long-term hemodialysis patients. Several of these guidelines have been selected as clinical performance measures by regulatory agencies to drive the process of quality improvement in long-term dialysis patients, and an initiative in the United States called “Fistula First” recently was started in an effort to increase the percentage of patients who have an arteriovenous fistula placed for long-term hemodialysis therapy.
Several major changes have occurred since the publication of the first set of guidelines. First, a number of clinical trials have been performed to determine the efficacy of different methods of identifying an access that is beginning to fail. Thus, this update of the guideline includes a substantial revision of accepted methods for access dysfunction detection. Second, cannulation techniques have been updated to include the importance of training staff in cannulation techniques and the appropriate uses of the buttonhole technique for arteriovenous fistulae. Finally, urokinase was removed from the market and other thrombolytic agents have been developed to assist with reestablishing patency in dialysis catheters. The use of these newer agents is addressed in this update.
This document has been divided into 3 major areas. The first section consists of guideline statements that are evidence based. The second section is a new section that consists of opinion-based statements that we are calling “clinical practice recommendations,” or CPRs. These CPRs are opinion based and are based on the expert consensus of the Work Group members. It is the intention of the Work Group that the guideline statements in Section I can be considered for clinical performance measures because of the evidence that supports them. Conversely, because the CPRs are opinion based, and not evidence based, they should not be considered to have sufficient evidence to support the development of clinical performance measures. The third section consists of research recommendations for these guidelines and CPRs. We have decided to combine all the research recommendations for the guidelines into 1 major section and also have ranked these recommendations into 3 categories: critical importance, high importance, and moderate importance. Our intended effect of this change in how the research recommendations are presented is to provide a guidepost for funding agencies and investigators to target research efforts in areas that will provide important information to benefit patient outcomes.
This final version of the Clinical Practice Guidelines and Recommendations for Vascular Access has undergone extensive revision in response to comments during the public review. While considerable effort has gone into their preparation during the past 2 years and every attention has been paid to their detail and scientific rigor, no set of guidelines and clinical practice recommendations, no matter how well developed, achieves its purpose unless it is implemented and translated into clinical practice. Implementation is an integral component of the Kidney Disease Outcomes Quality Initiative (KDOQI) process and accounts for the success of its past guidelines. The Kidney Learning System (KLS) component of the National Kidney Foundation is developing implementation tools that will be essential to the success of these guidelines.
In a voluntary and multidisciplinary undertaking of this magnitude, many individuals make contributions to the final product now in your hands. It is impossible to acknowledge them individually here, but to each and every one of them, we extend our sincerest appreciation. This limitation notwithstanding, a special debt of gratitude is due to the members of the Work Group and their co-chairs, Anatole Besarab of Henry Ford Hospital and Jack Work of Emory University. It is their commitment and dedication to the KDOQI process that has made this document possible.
Adeera Levin, MD, FACP
Michael Rocco, MD, MSCE
More than 300,000 individuals in the United States rely on a vascular access to receive hemodialysis (HD) treatment.1 Vascular access continues to be a leading cause for hospitalization and morbidity in patients with chronic kidney disease (CKD) stage 5.2 Appropriate care of HD patients with CKD stage 5 requires constant attention to the maintenance of vascular access patency and function. An ideal access delivers a flow rate to the dialyzer adequate for the dialysis prescription, has a long use-life, and has a low rate of complications (eg, infection, stenosis, thrombosis, aneurysm, and limb ischemia). Of available accesses, the surgically created fistula comes closest to fulfilling these criteria. Studies over several decades consistently demonstrate that native fistula accesses have the best 4- to 5-year patency rates and require the fewest interventions compared with other access types.3-5 However, in the United States between 1985 and 1995, the growth of the CKD Stage 5 HD program was accompanied by decreased use of native fistulae and increased use of grafts and cuffed central catheters for permanent HD access.5,6 In 1995, the United States Renal Data System (USRDS) reported, for the 1990 incident cohort of patients, that insertion of polytetrafluoroethylene (PTFE) grafts occurred almost twice as often as construction of native accesses.6 Significant geographic variation in the ratio of native fistula construction to graft placement also was noted.
The substitution of grafts for fistulae increased patient care costs, in part because of the increased number of procedures needed to maintain patency of grafts compared with native fistulae.7 A review of Medicare billing showed that the first-year total yearly costs for patients initiating HD therapy using a fistula were lowest ($68,002) compared with grafts ($75,611) and catheters ($86,927).8 Although the second-year total yearly costs were lower for all groups, catheters still resulted in the highest costs at $57,178 compared with $54,555 for grafts and $46,689 for fistulae. Similarly, in a single-center Canadian study, the cost of vascular access–related care was lower by more than 5-fold for patients who began the study period with a functioning fistula compared with those treated with a long-term catheter or graft.9
Before the first dissemination of the Dialysis Outcomes Quality Initiative (DOQI) recommendations on vascular access in 1997, many studies showed that practice patterns were contributing to patient morbidity and mortality, as well as costs. The failure of access was noted to be a major cause of morbidity for patients on HD therapy, with a number of reports indicating that a high percentage of hospitalizations for patients with CKD stage 5 were caused by vascular access complications.6,7,10-12 The USRDS reported that HD access failure was the most frequent cause of hospitalization for patients with CKD stage 5,6 and, in some centers, it accounted for the largest number of hospital days.13 Reports also indicated a decreasing interval between placement of a vascular access and a surgical procedure needed to restore patency,7,12 with significant costs to restore patency.6,13 Since then, a study using data from the USRDS Morbidity and Mortality Study Wave 1 showed that patients receiving catheters and grafts have greater mortality risk than patients dialyzed with fistulae.14 In patients with and without diabetes mellitus, cause-specific analyses found higher infection-related deaths for cuffed central catheters. In patients without diabetes, relative risks (RRs) were 1.83 (P < 0.04) with catheters and 1.27 (P < 0.33) with arteriovenous (AV) grafts (AVGs). In patients with diabetes, the RR was even higher than in those without diabetes: RR of 2.30 (P < 0.06) for catheters and RR of 2.47 (P < 0.02) for grafts compared with fistulae. Cardiac cause of death was highest in patients with central venous catheters (CVCs). A number of subsequent epidemiological studies, both in the United States15,16 and abroad,17 reaffirmed that greater use of fistulae was associated with reduced mortality and morbidity.
It was shown that an aggressive policy for monitoring hemodynamics within an AVG or AV fistula (AVF) to detect access dysfunction may reduce the rate of thrombosis (see Clinical Practice Guideline [CPG] 4). Thus, much access-related morbidity and associated costs might be avoided. The number of interventions required to maintain access patency may be decreased further by the use of fistulae rather than AVGs. Studies showed that the number of access events is 3- to 7-fold greater in prosthetic bridge grafts than in fistulae,3,18 thereby contributing to the increased cost of grafts. Whether utilization of such interventions to reduce thrombosis rates ultimately prolongs the useable life of the access are unknown and should not be the sole outcome measure. Thrombosis is associated with additional risks to the patient that are not present with simple percutaneous angioplasty (PTA).19
The National Kidney Foundation (NKF) issued the Kidney Disease Outcomes Quality Initiative (KDOQI) CPGs for Vascular Access in an effort to improve patient survival and quality of life (QOL), reduce morbidity, and increase efficiency of care. Vascular access patency and adequate HD are essential to the optimal management of HD patients with CKD stage 5. The first is a necessary prerequisite for the second. To improve QOL and overall outcomes for HD patients, 2 primary goals were originally put forth in the vascular access guidelines20:
Increase the placement of native fistulae
Detect access dysfunction before access thrombosis.
We believe these goals still apply, with the emphasis on placement of the functioning fistula. The Centers for Medicare & Medicaid Services (CMS) has actively collected data on 3 Clinical Performance Measures (CPMs) derived from the original and revised KDOQI Guidelines for Vascular Access. The failure to “adequately” increase the number of fistulae among either incident or prevalent HD patients during the past 6 years2 or to reduce the use of catheters led to a CMS mandate that the ESRD networks develop Quality Improvement Projects (QIPs) on Vascular Access. These have been distilled into 3 key points: avoid central catheterization, thus avoiding loss of central patency; maintain existing access by detecting impending failure, followed by prompt intervention; and maximize creation of fistulae as the best long-term access. Out of these concepts has grown the National Vascular Access Improvement Initiative (NVAII), emphasizing a fistula-first approach. Recently, the target for fistula creation was set as 65% by 2009 (www.cms.hhs.gov/ESRDQualityImproveInit/04_FistulaFirstBreakthrough.asp). The Work Group acknowledges the importance of increasing the number of fistulae in use, but believes that the emphasis should be shifted from the fistula construction rate to the rate of usable fistula accesses. This shift in emphasis is important to minimize wasted time and effort and reduce the primary failure rate and salvage procedures.
A number of barriers need to be overcome to achieve the goals set for vascular fistula construction; chief among these is the late referral of patients for permanent access placement, reflected in patient hospitalizations. In some regions, up to 73% of patients are hospitalized for initiation of HD therapy, almost invariably for dialysis catheter access placement.21 Unexpectedly, the modest increases in fistula use rates have been accompanied by increases in the use of catheters.2 Early referral of patients with CKD stage 5 to a nephrologist is absolutely essential to allow for access planning and thus increase the probability of fistula construction and maturation, thereby decreasing the need for catheter placement.
To achieve these objectives, the current Work Group has developed and revised the vascular access practice guidelines and strategies for implementation and has made a concerted effort to differentiate guidelines from recommendations. At the core of these guidelines is the goal of early identification of patients with progressive kidney disease and the identification and protection of potential fistula construction sites—particularly sites using the cephalic vein—by members of the health care team and patients.
After access has been constructed, dialysis centers need to use a multifaceted continuous quality improvement (CQI) program to detect vascular accesses at risk, track access complication rates, and implement procedures that maximize access longevity. Vascular access databases that are available to all members of the vascular access team (VAT) are crucial. The Work Group has developed explicit guidelines regarding which tests to use to evaluate a given access type and when and how to intervene to reduce thrombosis and underdialysis. The Work Group believes that the guidelines are reasonable, appropriate, and achievable. Attainment of these goals will require the concerted efforts of not only practicing nephrologists, but also nephrology nurses, access surgeons, vascular interventionalists, patients, and other members of the health care team.
In this update of the Vascular Access Guidelines, the Work Group did not perform a comprehensive review of all the guidelines. Seven topics underwent systematic review, and these are identified. The other guidelines were unified and consolidated. More recent references, including reviews, were included when appropriate.
I. CLINICAL PRACTICE GUIDELINES FOR VASCULAR ACCESS
Guideline 1. Patient preparation for permanent hemodialysis access
Appropriate planning allows for the initiation of dialysis therapy at the appropriate time with a permanent access in place at the start of dialysis therapy.
Patients with a glomerular filtration rate (GFR) less than 30 mL/min/1.73 m2 (CKD stage 4) should be educated on all modalities of kidney replacement therapy (KRT) options, including transplantation, so that timely referral can be made for the appropriate modality and placement of a permanent dialysis access, if necessary. (A)
In patients with CKD stage 4 or 5, forearm and upper-arm veins suitable for placement of vascular access should not be used for venipuncture or for the placement of intravenous (IV) catheters, subclavian catheters, or peripherally inserted central catheter lines (PICCs). (B)
Patients should have a functional permanent access at the initiation of dialysis therapy.
A fistula should be placed at least 6 months before the anticipated start of HD treatments. This timing allows for access evaluation and additional time for revision to ensure a working fistula is available at initiation of dialysis therapy. (B)
A graft should, in most cases, be placed at least 3 to 6 weeks before the anticipated start of HD therapy. Some newer graft materials may be cannulated immediately after placement. (B)
A peritoneal dialysis (PD) catheter ideally should be placed at least 2 weeks before the anticipated start of dialysis treatments. A backup HD access does not need to be placed in most patients. A PD catheter may be used as a bridge for a fistula in “appropriate” patients. (B)
Evaluations that should be performed before placement of a permanent HD access include (Table 1):
History and physical examination, (B)
Duplex ultrasound of the upper-extremity arteries and veins, (B)
Central vein evaluation in the appropriate patient known to have a previous catheter or pacemaker. (A)
Since implementation of the NKF KDOQI Vascular Access Guidelines in 1997, which encouraged increased placement of fistulae, CMS has embraced this recommendation with the implementation of the Fistula First Breakthrough Initiative (FFBI). This initiative endorses the goals recommended by the NKF KDOQI: fistula rates of 50% or greater for incident—and at least 40% for prevalent—patients undergoing HD. The FFBI promotes the placement of fistulae in all suitable HD patients. Working through the ESRD Networks, the FFBI promotes the placement of fistulae using 11 “Change Concepts” that encourage the development of specific strategies; these 11 Change Concepts have been identified to help the kidney community improve the rate of fistula placement. Five of these strategies emphasize the same goals as CPG 1 and Clinical Practice Recommendation (CPR) 1: education of patients regarding fistulae, protection of vessels, vessel mapping, and sufficient lead-time for fistula maturation (NVAII; www.fistulafirst.org). The breakthrough initiative has reset the goal for fistula creation to 65% by 2009.
Characteristics of a patient’s arterial, venous, and cardiopulmonary systems will influence which access type and location are most desirable for each patient.22-27 The patient’s life expectancy and planned duration of CKD stage 5 therapy also can influence the type and location of the access. All patients should be evaluated as in Table 1.
Venipuncture complications may render veins potentially available for vascular access unsuitable for construction of a primary fistula. Patients and health care professionals should be educated about the need to preserve veins to avoid loss of potential access sites in the arms and maximize chances for successful fistula placement and maturation. Subclavian vein catheterization is associated with central venous stenosis.28-30 Significant subclavian vein stenosis generally will preclude the use of the entire ipsilateral arm for vascular access. Thus, subclavian vein catheterization should be avoided for temporary access in patients with kidney disease.31 The incidence of central vein stenosis and occlusion after upper-extremity placement of peripherally inserted long-term catheters (PICCs) and venous ports was 7% in 1 retrospective study of 150 patients.32 PICCs also are associated with a high incidence of upper-extremity thrombosis. The incidence of upper-extremity venous thrombosis varies between 11% and 85%, which leads to loss of potential upper-extremity fistulae.33-35 Because of the substantial risk for loss of useable upper-extremity veins and central venous stenosis with PICCs, the Work Group recommends strongly that PICCs not be used in patients with CKD.
Ideally, patients should have a functional permanent access at the time of dialysis therapy initiation. Function implies that the access not only delivers adequate blood flow for dialysis, but may be cannulated easily. In general, such an access has a flow of approximately 600 mL/min, is less than 0.6 cm below the surface of the skin, and has a minimal diameter of 0.6 cm (Rule of 6s) Both the size and anatomic qualities of venous and arterial components of primary fistulae can influence fistula maturation time. An aggressive policy of primary fistula creation may result in failures in patients with marginal anatomy. However, timely attempts to create a primary fistula before the anticipated need for dialysis therapy will allow adequate time for the fistula to mature and will allow sufficient time to perform another vascular access procedure if the first attempt fails, thus avoiding the need for temporary access. Early referral of a patient with CKD to a nephrologist is needed to facilitate CKD therapy with medications and diets that preserve kidney function. In addition, counseling patients about CKD stage 5 treatment options is essential to plan for ideal access (ie, PD and HD access) (see CPG 2) (Table 1).
The Work Group’s consensus is that maturation of an AVG access site—defined as reduction of surgically induced swelling and the graft’s adherence to its tunnel tissue—usually requires about 3 weeks. Thus, ideally, AVGs should be placed 3 to 6 weeks before use.
Long-term catheters are the method of choice for temporary access of longer than 1 week duration. Catheters are suitable for immediate use. To maximize their use-life, they should not be inserted until needed. However, the Work Group recommends that a catheter be used for dialysis access for as brief a period as necessary (see CPG 2).
A vein must be mature, both physically and functionally, before use for vascular access. The time required for fistula maturation varies among patients. The Work Group does not advise use of the fistula within the first month after construction because premature cannulation of a fistula may result in a greater incidence of infiltration, with associated compression of the vessel by hematoma and permanent loss of the fistula. In general, allowing the fistula to mature for 6 to 8 weeks before investigating the reason for failure to mature is appropriate (see CPG 2). For a fistula to be considered successful, it must be usable. In general, a working fistula must have all the following characteristics: blood flow adequate to support dialysis, which usually equates to a blood flow greater than 600 mL/min; a diameter greater than 0.6 cm, with location accessible for cannulation and discernible margins to allow for repetitive cannulation; and a depth of approximately 0.6 cm (ideally, between 0.5 to 1.0 cm from the skin surface). This combination of characteristics can be remembered easily as the Rule of 6s.
Although there are no definitive data in the literature, any intervention that increases blood flow to the extremity may improve the chances of successful fistula development. Therefore, regular hand-arm exercises, with or without a lightly applied tourniquet, are recommended until the fistula matures. Failure of a fistula to mature occasionally is caused by venous side branches that drain critical flow from the primary vessel. Ligating these side branches may result in successful maturation (see CPG 6).
Studies relating to preoperative venous imaging/mapping for AVF construction underwent systematic review. Duplex ultrasound is the preferred method for preoperative vascular mapping. Vascular mapping in preparation for the creation of a vascular access refers to the evaluation of vessels, both arterial and venous, of patients with CKD who have selected HD therapy, and it should be performed in all patients before placement of an access. Preoperative vascular mapping was shown to substantially increase the total proportion of patients dialyzing with fistulae.36-39 Several studies support the 2.0- to 2.5-mm vein diameter threshold for successful creation of a fistula.39,40 Radiocephalic fistulae constructed in veins less than 2.0 mm in diameter had only a 16% primary patency at 3 months compared with 76% for those with veins greater than 2.0 mm.40 In a pivotal study,39 a threshold of 2.5-mm vein diameter, assessed by using duplex ultrasound, was used; this resulted in an increase in fistula creation to 63% compared with a retrospective 14% rate in the absence of vascular mapping.22 A similar study using the same duplex ultrasound criteria showed a fistula increase from 34% in historical controls to 64%. Importantly, in this study, duplex ultrasound altered the surgical plan based entirely on the surgeon’s clinical evaluation, resulting in increased placement of fistulae.41
There is no generally accepted “standard” for what constitutes vascular mapping. The arterial evaluation should include pulse examination, differential blood pressure measurement, assessment of the palmar arch for patency, arterial diameter assessed by using duplex ultrasound, and the presence of arterial calcification. A preoperative arterial diameter less than 1.6 mm has been associated with a high failure rate in radiocephalic fistulae.42,43 Other studies suggested that a minimum diameter of 2.0 mm is required for successful fistula creation.39 Venous evaluation should include a luminal diameter of 2.5 mm or greater, continuity with the proximal central veins, and absence of obstruction.39 The central veins may be assessed indirectly by using duplex ultrasound.44 Compared with invasive venography, duplex ultrasound had a specificity of 97% and sensitivity of 81% for detecting central vein occlusion.45 Alternatively, venography or magnetic resonance angiography (MRA) may be used to evaluate central veins.46 (See CPR 1.4 for suitable imaging studies for central veins).
There has been no study comparing vascular access surgery based only on the clinical evaluation to preoperative vascular mapping outcomes. Such a study would be the equivalent of requiring a randomized prospective study comparing the efficacy of pulmonary clinical evaluation (tactile fremitus and auscultation, ie, physical examination only) with a chest radiograph (imaging) in identifying lung pathological states. Such a study is unlikely, based on current data showing that vascular mapping increases fistula creation. Although the level of evidence of a prospective randomized trial is not available, the Work Group consensus based on many studies supports vascular mapping as a guideline.
Guideline 2. Selection and placement of hemodialysis access
A structured approach to the type and location of long-term HD accesses should help optimize access survival and minimize complications.
The access should be placed distally and in the upper extremities whenever possible. Options for fistula placement should be considered first, followed by prosthetic grafts if fistula placement is not possible. Catheters should be avoided for HD and used only when other options listed are not available.
The order of preference for placement of fistulae in patients with kidney failure who choose HD as their initial mode of KRT should be (in descending order of preference):
Preferred: Fistulae. (B)
A wrist (radiocephalic) primary fistula. (A)
An elbow (brachiocephalic) primary fistula. (A)
A transposed brachial basilic vein fistula: (B)
Acceptable: AVG of synthetic or biological material, such as: (B)
A forearm loop graft, preferable to a straight configuration.
Chest wall or “necklace” prosthetic graft or lower-extremity fistula or graft; all upper-arm sites should be exhausted.
Avoid if possible: Long-term catheters. (B)
Short-term catheters should be used for acute dialysis and for a limited duration in hospitalized patients. Noncuffed femoral catheters should be used in bed-bound patients only. (B)
Long-term catheters or dialysis port catheter systems should be used in conjunction with a plan for permanent access. Catheters capable of rapid flow rates are preferred. Catheter choice should be based on local experience, goals for use, and cost. (B)
Long-term catheters should not be placed on the same side as a maturing AV access, if possible. (B)
Special attention should be paid to consideration of avoiding femoral catheter access in HD patients who are current or future kidney transplant candidates. MRA imaging of both arteries and veins is the diagnostic procedure of choice for evaluating central vessels for possible chest wall construction.
Patients should be considered for construction of a primary fistula after failure of every dialysis AV access. (B)
While this order of access preference is similar for pediatric patients, special considerations exist that should guide the choice of access for children receiving HD. Please refer to CPG 9 for specific recommendations.
In the patient receiving PD who is manifesting signs of modality failure, the decision to create a backup fistula should be individualized by periodically reassessing need. In individuals at high risk for failure (see the PD Adequacy Guidelines), evaluation and construction should follow the procedures in CPG 1 for patients with CKD stage 4.
Enhanced maturation of fistulae can be accomplished by selective obliteration of major venous side branches in the absence of a downstream stenosis. (B)
The choice of synthetic or biological material should be based on the surgeon’s experience and preference. The choice of synthetic or biological conduits should consider local experience, technical details, and cost. (B)
There is no convincing evidence to support tapered versus uniform tubes, externally supported versus unsupported grafts, thick- versus thin-walled configurations, or elastic versus nonelastic material. (A)
While the majority of past experience with prosthetic grafts has been with the use of PTFE, other prosthetics (eg, polyurethane [PU]) and biological conduits (bovine) have been used recently with similar outcomes. (B)
Patients with swelling that does not respond to arm elevation or that persists beyond 2 weeks after dialysis AV access placement should receive an imaging study or other noncontrast study to evaluate central venous outflow (see CPG 1). (B)
Catheters and port catheter systems:
The preferred insertion site for tunneled cuffed venous dialysis catheters or port catheter systems is the right internal jugular vein. Other options include the right external jugular vein, left internal and external jugular veins, subclavian veins, femoral veins, and translumbar and transhepatic access to the IVC. Subclavian access should be used only when no other upper-extremity or chest-wall options are available. (A)
Ultrasound should be used in the placement of catheters. (B)
The position of the tip of any central catheter should be verified radiologically. (B)
Order of Placement (CPG 2.1)
There are no randomized controlled trials (RCTs) comparing the recommended anatomic order of distal-to-proximal access construction. However, good surgical practice makes it obvious that when planning permanent access placement, one should always consider the most distal site possible to permit the maximum number of future possibilities for access.23 In general, a peripheral-to-central sequence of fistulae construction should be envisioned in the ideal case, beginning with the “snuff box” fistula at the base of the thumb, followed by the standard Brescia-Cimino wrist fistula, followed by a forearm cephalic fistula at dorsal branch and finally a midforearm cephalic fistula. If a forearm fistula is not feasible, an antecubital fistula,47 cephalic fistula at elbow, and, finally, a transposed basilic fistula should be considered. In cases in which a fistula is not constructed initially, a graft can be used as a “planned bridge” to a fistula. Failing forearm grafts can be converted to upper-arm fistulae, and lower-level fistulae can be converted to higher-level fistulae. If a graft is constructed, preference is given to the following sequence: forearm loop; upper-arm, straight or curved; upper-arm loop. All upper-extremity options should be considered before using the thigh. At times, “exotic” grafts can be constructed on the anterior chest wall or to the internal jugular vein. Even in these situations, a systematic radiological evaluation of the venous systems should be conducted before placement.
Maintaining long-term functioning access can be difficult and frustrating for physicians and patients; starting distally and moving proximally provides for the possibility of preserving as many potential sites as possible for future access creation. It is a tragedy for patients and caretakers alike to exhaust anatomic sites prematurely by initially bypassing more distal sites. The decision to use a more proximal site initially should be documented by preoperative imaging studies or the likelihood for the development of arterial “steal.”23,48 (See CPGs 1, 5, and 6.) However, if upper-extremity options have been exhausted, the anatomic locations left for permanent access are the thigh (where grafts49,50 and, less commonly, fistulae51 can be constructed) and upper chest, where a variety of graft accesses can be constructed.52 The possibilities in the chest usually are defined by preoperative evaluation of the central venous system and, at times, angiography53 or MRA is required.54 Because vascular access infection is intrinsically more likely in the thigh, access construction in this site usually is deferred to one of last resort. Graft patency in the thigh is minimally better than in the upper arm,55 and the greater risk for infection mandates against its initial use. In extreme cases, the forgotten Thomas shunt can be constructed.56
The preference of fistulae over all other forms of access arises from their functional advantages because of a lower rate of complications.
Fistulae have the lowest rate of thrombosis57 and require the fewest interventions,57,58 providing longer survival of the access.3,4,57,58 The number of access events is 3- to 7-fold greater in prosthetic bridge grafts than in native fistulae.4,57,58
As a result, costs of implantation and access maintenance are the lowest.4,6,8
Fistulae have lower rates of infection than grafts, which, in turn, are less prone to infection than percutaneous catheters and subcutaneous port catheter systems.59 Vascular access infections in HD patients are common, can be severe, and contribute to infection as the second leading cause of death in patients with CKD stage 5.60
Fistulae are associated with increased survival and lower hospitalization.
Patients receiving catheters (RR = 2.3) and grafts (RR = 1.47) have a greater mortality risk than patients dialyzed with fistulae.14
Epidemiological evidence also indicates that greater use of fistulae reduces mortality and morbidity.14-17
Wrist (radiocephalic)61 and elbow (brachiocephalic)62 primary fistulae are the preferred types of access because of the following characteristics:
Superior patency to other accesses after they are established and matured.3,4,23,24,57,58,63-69
Lower complication rates compared with other access options,3,23,24,63-69 including lower incidence of conduit stenosis, infection, and vascular steal phenomenon.
In most cases, flow increases early (first week), with little additional increase as the fistula matures (see CPG 5).70-72 Failure of fistula flow to increase is a sign of access dysfunction (see CPG 4).
The Work Group concluded that the 3 advantages of wrist and elbow primary fistulae, as listed, outweigh the following 4 potential disadvantages:
The vein may fail to enlarge and/or increase blood flow to satisfactory levels (ie, fail to mature).23,24,73
Comparatively long maturation times (1 to 4 months) must elapse after creation of these fistulae before they can be used. Thus, the access must be created several months in advance of the anticipated need for dialysis or an alternative temporary method of vascular access must be used while the fistula matures (see CPG 1).
In some individuals, the vein may be more difficult to cannulate than an AVG. However, this can be addressed by mobilizing the vein superficially.74
The enlarged vein may be visible in the forearm and be perceived as cosmetically unattractive by some individuals.
The wrist fistula is the first choice of access type because of the following advantages:
It is relatively simple to create.61,75
It preserves more proximal vessels for future access placement.23,24,73
It has few complications. Specifically, the incidence of vascular steal is low, and in mature fistulae, thrombosis and infection rates are low.3,4,24,57,58,65,66
The only major disadvantage of the wrist (radiocephalic) fistula is a lower blood flow rate (BFR) compared with other fistula types. If adequate flow to support the HD prescription is not achieved with a radiocephalic fistula within 4 months after appropriate evaluation for correctable or modifiable factors (see CPG 4), another type of access should be established (see CPG 1). The major drawback of a radiocephalic fistula is the relatively high primary failure rate (15%) and only moderate secondary patency rate at 1 year (62%).76
The elbow (brachiocephalic) primary fistula is the second choice for initial placement of an access. Its advantages include the following:62,63,68,77-79
It has a higher blood flow compared with the wrist fistula.
The cephalic vein in the upper arm usually is comparatively easier to cannulate and is easily covered, providing a potential cosmetic benefit.
The disadvantages of the elbow (brachiocephalic) primary fistula include the following:26,66,77-80
It is slightly more difficult to create surgically than a radiocephalic fistula.
It may result in more arm swelling than a radiocephalic fistula.
It is associated with an increased incidence of steal compared with a radiocephalic fistula.
It is associated with a greater incidence of cephalic arch stenosis than a forearm radiocephalic fistula.
If a wrist radiocephalic or elbow brachiocephalic fistula cannot be created, the patient should be considered for a transposed basilic vein fistula. In some cases, a forearm graft can be a viable alternative to mature the venous system for an elbow fistula as a secondary access. Transposed brachiobasilic fistulae have several disadvantages compared with other fistulae:62,66,79,81-83
The transposition procedure may create significant arm swelling and patient pain.
They have a greater incidence of steal and arm swelling than other fistula types.
They are more technically challenging, especially in obese individuals.
The NVAII, now recognized as the FFBI, is a CMS-mandated 3-year CKD Stage 5 Network improvement project emphasizing a fistula-first approach.84-88 The Work Group agrees with the “mission statement” to “increase the likelihood that every eligible patient will receive the most optimal form of vascular access for him/her, in the majority of cases an arterial venous fistula.” For FFBI to optimally succeed, all its recommendations must be followed (NVAII, www.fistulafirst.org; last accessed 2/20/2006). However, the Work Group recognizes that in some cases, the “fistula first at all costs” approach may not be the most cost-effective or optimal for each individual. A functional fistula is the goal, not the insertion of a fistula with a poor chance at maturing. A graft can be used as a “planned bridge” to a fistula, and failing forearm grafts can be converted to upper-arm fistulae. Similarly, fistulae at a lower level can be converted to more proximal fistulae.
AVGs have the following advantages:
A large surface area and vessel available for cannulation initially.64,89-91
They are technically easy to cannulate.64
The lag-time from insertion to maturation is short. For PTFE-derived grafts, it is recommended that not less than 14 days should elapse before cannulation to allow healing and incorporation of the graft into local tissues,25,64,92 although ideally, 3 to 6 weeks are recommended.
Multiple insertion sites are available.26,64,67,90-94
A variety of shapes and configurations is available to facilitate placement.64,67,89-92,94
It is easy for the surgeon to handle, implant, and construct the vascular anastomosis.25,26,64,91,92,94-104
The graft is comparatively easy to repair either surgically65,94,101,105-107 or endovascularly.108-112
The sum of the available data, until recently, supported PTFE grafts over other biological and other synthetic materials, based on lower risk for disintegration with infection, longer patency, better availability, and improved surgical handling. Biological grafts (bovine heterografts) have greater reported rates of complications compared with synthetic grafts.91-93,100
For nearly 2 decades, PTFE has been the material of choice for bridge grafts. However, during the past decade, modifications113 and the use of other materials, such as PU,114,115 cryopreserved femoral vein,116,117 bovine mesenteric vein, and hybrids118 with self-sealing composite material, have been developed and used.119 None of these has shown any “survival” patency over plain PTFE, except for the composite/PU graft. The latter has an advantage because of its self-sealing property to be cannulated within hours, if needed, for dialysis. As a result, it can be placed without having to use a catheter for initiation of dialysis therapy, in some cases. Direct comparisons between PTFE and human umbilical cord vein grafts and other synthetic polymers have not been made.
The lure to construct AVGs using larger more proximal vessels should be resisted. Although these have higher flow and better initial function and/or patency, they limit potential sites for future placement.23,25,73 A synthetic dialysis AVG is expected to last 3 to 5 years.73 Grafts using smaller more peripheral vessels can experience more frequent thromboses that require treatment. However, these grafts have the advantage of preserving more proximal sites for new access creation should this become necessary in the future.4,23-25 The 2 preferred graft site types are the antecubital loop graft and upper-arm curved graft. Femoral placement of access has been associated with proximal venous stenosis, which may be problematic later in patients receiving kidney transplantation.
Potential sites for arterial inflow include radial artery at the wrist, brachial artery in the antecubital fossa, brachial artery in the lower portion of the arm, brachial artery just below the axilla, axillary artery, and femoral artery. Potential sites for venous outflow include median antecubital vein, proximal and distal cephalic vein, basilic vein at the level of the elbow, basilic vein at the level of the upper arm, axillary vein, jugular vein, and femoral vein.
Fistulae (CPG 2.2)
A 70% AV “working” fistula access rate can be achieved, even in patients who have diabetes85-88 and women.84 Results from the Dialysis Outcomes and Practice Patterns Study (DOPPS) indicate that the fistula can be cannulated as early as 1 month after construction.120 Thus, an access that shows evidence of maturation failure on physical examination or by using duplex ultrasound72 should undergo investigation. A study found that combining venous diameter (>0.4 cm) and flow volume (>500 mL/min) increased the predictive power of adequate fistula maturation to 95% (19 of 20) versus neither criterion met (33%; 5 of 15).72 Women were less likely to have an adequate outcome vein diameter of 0.4 cm or greater: 40% (12 of 30) compared with 69% in men (27 of 39). However, of note, the accuracy of experienced dialysis nurses in predicting eventual fistula maturity was excellent at 80% (24 of 30).
Many accesses with multiple outflow veins can be salvaged by ligation of side branches.121,122 As more older patients have fistula constructions, the possibility of the access failing to mature is likely to increase.123 Failure to mature should be evaluated by 6 weeks after construction by physical examination and, if needed, ultrasound.72,124 Prompt correction should be undertaken.125,126
Exercises to Mature the Fistula (B-)
Isometric exercise has been shown to increase the diameter of forearm veins,127 and exercise should be prescribed if there is sufficient lead time before surgery.
Dialysis AVGs (CPG 2.3)
Graft patency is independent of manufacturer,128-130 unaffected by an external wrap around the graft,131 and is not affected by wall thickness.131,132 The provision of a cuff or hood at the venous outflow to enlarge the outflow and reduce shear stress has produced only a marginal increase in graft patency.133-136 To control inflow or shear stresses, a variety of tapers have been examined at both arterial and venous anastomoses. There seems to be little effect from using a 6- to 8-mm graft compared with the standard straight 6 mm.137 A straight 8 mm also can be used and gives the highest flows.138 Arterial tapers are used to restrict inflow and reduce the risk for steal syndrome. Their effectiveness is questionable, and they may negatively affect patency and survival.139
As previously discussed in CPG 2.1, a variety of modifications to the graft or other materials is available to the surgeon.113-119 Several studies are available to guide the interested reader.140-142 Predictors for successful placement of AVGs have been analyzed.143
The neointimal hyperplasia that produces stenosis has been considered to be, in part, a reaction to injury. No improvement in patency was noted in an RCT that compared staples with standard sutures at the vascular anastamoses.144 Use of nitinol surgical clips produces less intimal damage than conventional sutures,145 but RCTs showing a resulting change in outcome are lacking.
It should be remembered that a short segment of graft material can be used to develop a predominant fistula at the elbow.146
Catheters and Port Catheter Systems (CPG 2.4)
Long-term catheter systems—tunneled cuffed catheters (TCCs) and tunneled port catheter systems—should have their tips within the right atrium confirmed by fluoroscopy for optimal flow.
Short-term catheter tips should be in the superior vena cava (SVC) and confirmed by using chest radiograph or fluoroscopically at the time of placement before initiating dialysis therapy.
Uncuffed HD catheters should only be used in hospitalized patients and for less than 1 week. Uncuffed femoral catheters should only be used in bed-bound patients.
There should be a plan to: i) discontinue, or ii) convert any short-term catheter to a long-term catheter within 1 week.
Long-term catheters and port catheter systems, if possible, should not be placed on the same side as a maturing AV access.
Femoral catheters should be a suitable length to deliver high-volume flow and be positioned to minimize recirculation. One that does not reach the IVC frequently cannot deliver 300 mL/min. Longer catheters (24 to 31 cm) are more likely to reach the desired position, although there is more resistance from the catheter length.
There currently is no proven advantage of 1 long-term catheter design over another, although this area is undergoing a great deal of study. Catheters capable of a rapid BFR (>350 mL/min at prepump pressures not more negative than 250 mm Hg) are preferred. Catheter choice should be based on local experience, goals for use, and cost.
Pediatric exception: Some pediatric data exist suggesting that the twin-catheter system may provide better performance than the standard dual-lumen catheter configuration. Please refer to the Pediatric Guidelines.
Dialysis port catheter systems may be used in lieu of long-term catheters for a bridge access or as a permanent access for patients.
Catheter devices can be defined according to design, intent, and duration of use. For the entirety of the discussion, catheters will be referred to as acute short-term noncuffed catheters (NCCs) or long-term TCCs intended as access for dialysis over weeks to months. The term right arterial catheter should be avoided. They are either NCCs and placed predominantly for acute use (3 to 5 dialyses within 1 week) or TCCs and placed when the need for dialysis therapy is believed to be longer than 1 week. Long-term catheters usually are tunneled. The catheters themselves usually are dual lumen and can be coaxial (now unusual) or “double D” (most common) and are either stepped (ie, the arterial and venous tips are staggered by 1 to 2 cm) or split so that the tips are not next to each other. Newer designs incorporate a spiral separator allowing either lumen to be used as the arterial port catheter system.
Port catheter systems are a distinct kind of catheter-based device system in which the catheter tubing is connected to a subcutaneously placed device. In the only port device currently in use for HD, access to the catheter lumen occurs percutaneously by using a buttonhole technique. These port catheter systems have a pinch valve mechanism that requires special cannulation needles to open the valves accessing the circulation.
Tunneled Cuffed Venous Catheters
Tunneled cuffed venous catheters have been shown to have the following advantages, relative to other access types:
They are universally applicable.
They can be inserted into multiple sites relatively easily.
No maturation time is needed, ie, they can be used immediately.
Skin puncture not required for repeated vascular access for HD.
They do not have short-term hemodynamic consequences, eg, changes in cardiac output or myocardial load.
They have lower initial costs and replacement costs.
They possess the ability to provide access during a period of months, permitting fistula maturation in patients who require immediate HD.73,147-155
They facilitate correcting thrombotic complications.147,156-158
Tunneled cuffed venous catheters possess the following disadvantages relative to other access types:
High morbidity caused by:
Risk for permanent central venous stenosis or occlusion.30,148,160,161
Discomfort and cosmetic disadvantage of an external appliance.
Shorter expected use-life than other access types.64,69,156,162
Tunneled cuffed venous catheters should be placed in an area where ultrasound guidance and fluoroscopy are available. The preferred site is the right internal jugular vein because this site offers a more direct route to the right atrium than the left-sided great veins. Catheter insertion and maintenance in the right internal jugular vein are associated with a lower risk for complications compared with other potential catheter insertion sites.164-166 Catheter placement in the left internal jugular vein potentially puts the left arm’s vasculature in jeopardy for a permanent access on the ipsilateral side. Catheter placement in the left internal jugular vein may be associated with poorer BFRs and greater rates of stenosis and thrombosis.150,166 Femoral and translumbar vein placement are associated with the greatest infection rates compared with other sites.167 Catheters should not be placed in the subclavian vessels on either side because of the risk for stenosis,30,168 which can permanently exclude the possibility of upper-extremity permanent fistula or graft. Catheters should not be placed on the same side as a slowly maturing permanent access. Catheter-induced central vein stenosis is related to the site of insertion,169,170 number and duration of catheter uses, and occurrence of infection.170,171
Ultrasound insertion has been shown to limit insertion complications.172-174 Evidence is sufficient to recommend that ultrasound guidance be used for all insertions because it minimizes inadvertent arterial cannulation.175,176 Fluoroscopy allows ideal catheter tip placement177,178 to maximize blood flow.179 At the time of placement, the tip(s) of the catheter should be in the midatrium, with the arterial lumen facing the mediastinum.
Use of catheters presents a conundrum because of the need for immediate vascular access versus the risk for complications from prolonged catheter use.180 Blood flow for dialysis obtained from catheters typically is less than that obtained from fistulae or grafts.2 Catheter length becomes crucial when TCCs are placed in the femoral area or through the translumbar or transhepatic routes.181 Correlations between arterial prepump or venous return pressures and dialyzer blood flows are not linear.182,183 It is possible to develop an optimal relationship between catheter length and diameter to achieve standardized (average, low, and high) blood flows regardless of the lengths of the catheters by incorporating the pressure-flow relationships, as well as Poiseuille’s equation.183
Use of catheters as first choice for long-term vascular access is discouraged because of infection, susceptibility to thrombosis, and inconsistent delivery of blood flow. In patients with documented inadequate vascular access anatomy, use of catheters is feasible with both double-lumen184-188and twin-catheter systems.189-191 However, exceptions may occur in children.
In the United States, the demand for greater blood flows to reduce treatment times has resulted in catheters with larger lumens being placed. A variety of catheters can consistently deliver a flow greater than 350 mL/min to the dialyzer at prepump pressure of −200 to −250 mm Hg. The decision to use a step or a split design should be decided by local preferences. In general, all catheters will develop recirculation at some point,182,192 particularly if the arterial and venous blood tubing are reversed for any reason.193 This is minimized by using a split-tip catheter,194,195 but other designs are likely to produce the same effect.
The decision to use the femoral vein for long-term access (catheter or graft) as reported by some196,197 should be undertaken with great care. Any patient who has the option of undergoing a kidney transplantation should not have a femoral catheter placed to avoid stenosis of the iliac vein, to which the transplanted kidney’s vein is anastomosed. The Work Group recommends the concept of shared governance in this type of decision,198 with both dialysis staff and transplant team planning long-term access for such patients. There are no data on the effect of catheter length from the femoral vein site. Although length increases resistance, it also reaches anatomic sites with greater IVC flow. If dialysis blood flow is less than 300 mL/min from a properly placed femoral catheter, guidewire exchange to a longer catheter should be considered.
Noncuffed Double-Lumen Catheters
These catheters are suitable for percutaneous bedside insertion and provide acceptable BFRs (300 mL/min) for temporary HD.64,147,161,199,200 These catheters are suitable for immediate use, but have a finite use-life and therefore should not be inserted until they are needed.64,147,161 The rate of infection for internal jugular catheters suggests they should be used for no more than 1 week.60,64,147,161,201,202 Infection and dislodgment rates for femoral catheters require that they be left in place for no more than 5 days and only in bed-bound patients with good exit-site care. To minimize recirculation, femoral catheters should be at least 19 cm long to reach the IVC.203 The Work Group believes that TCCs are preferred for longer durations of HD therapy over NCCs because they are associated with lower infection rates and greater BFRs.60,64,147,149,151-153,155,161,184,201-204 Short-term catheters may be used for up to 1 week. Beyond 1 week, the infection rate increases exponentially. Actuarial analysis of 272 catheters (37 TCCs versus 235 NCCs) showed a difference in infection rates by 2 weeks.205 Infection rates per 1,000 days at risk for NCCs were more than 5 times as great as with internal jugular TCCs and almost 7 times greater with femoral NCCs.205
Ultrasound-directed cannulation of NCCs minimizes insertion complications, as it does with TCCs, and should be used when available.206,207 Because most NCCs are placed at the bedside, the need for a postinsertion chest radiograph after internal jugular or subclavian insertion is mandatory to confirm the position of the catheter tip in the SVC and exclude such complications as pneumothorax and hemothorax.28,64,147,151,208-212 Although there are no studies reporting on the safety of patients with NCCs going home while awaiting placement at a dialysis center, the Work Group believes that the risk for infection, inadvertent removal, hemorrhage, air embolism, and patient comfort mandates that patient safety come first. Therefore, a patient with an NCC should not be discharged. A short-term catheter can be converted to a TCC if there is no evidence of active infection.213
Port Catheter Systems
In an effort to surmount many of the infection problems associated with long-term catheters, totally implantable access systems have been designed.214,215 Clinical data support the use of subcutaneous HD access systems as a bridge device216-218 in patient populations at greater risk for fistula maturation failure or needing longer periods to mature fistulae (>1 operation or multiple attempts need to be made). Studies also documented the utility of subcutaneous HD access systems in catheter-dependent patients who have exhausted other access options219 and in children.220 The most significant limitation of these devices has been infection, particularly of the implantation pocket. Although these can be treated successfully,221 prevention is key. Recommended procedures for accessing and maintaining these devices are mandatory to achieve optimal device performance.
Complications of catheter access are detailed more fully in CPG 7, and accessing the patient’s circulation is discussed in CPG 3.
The recommendations made in this section are based on the best currently available information and basic principles of surgery. No RCTs will ever be performed comparing the 3 access types available, nor should they be in view of the known risks of catheters. However, developments in the future of synthetic materials or the prevention of neointimal hyperplasia may permit such trials.
Management of the patient who requires HD access for KRT demands continuous attention from the VAT. With the increase in incidence of HD-dependent patients with CKD within our population, the multidisciplinary KDOQI CPGs and CPRs presented provide a pathway and strategy for HD access insertion and/or creation. The most appropriate initial access depends on immediate need for HD, history and physical examination findings, and suitability of available veins in the extremity. Percutaneous catheter-based access affords the luxury of immediate access and absence of requirement for cannulation; however, these devices are plagued by their propensity for infection, thrombosis, inadequate blood flow, and—most importantly—damage to large central veins, leading to stenosis and jeopardizing long-term permanent access. The fistula access, while at times less successful in the immediate short term, is always the preferred long-term access type because of its greater longevity, fewer interventions for maintenance, and lower infection rates. The surgeon should focus on sites distally on the extremity, reserving proximal sites for potential future access insertions should the initial access site fail. In the absence of a suitable vein for a fistula, prosthetic access can be considered. When all sites in the upper extremities have been exhausted, the lower extremity or chest should be considered for access creation. Long-term catheters and port catheter systems should be reserved for last except in those with severe comorbidities, such as congestive heart failure (CHF) and severe peripheral vascular disease (PVD), the very elderly, those with inadequate vascular anatomy, or those with limited life expectancy.
Guideline 3. Cannulation of fistulae and grafts and accession of hemodialysis catheters and port catheter systems
The use of aseptic technique and appropriate cannulation methods, the timing of fistula and graft cannulation, and early evaluation of immature fistulae are all factors that may prevent morbidity and may prolong the survival of permanent dialysis accesses.
For all vascular accesses, aseptic technique should be used for all cannulation and catheter accession procedures. (SeeTable 2.) (A)
Maturation and cannulation of fistulae:
A primary fistula should be mature, ready for cannulation with minimal risk for infiltration, and able to deliver the prescribed blood flow throughout the dialysis procedure. (SeeTable 3.) (B)
Fistulae are more likely to be useable when they meet the Rule of 6s characteristics: flow greater than 600 mL/min, diameter at least 0.6 cm, no more than 0.6 cm deep, and discernible margins. (B)
Fistula hand-arm exercise should be performed. (B)
If a fistula fails to mature by 6 weeks, a fistulogram or other imaging study should be obtained to determine the cause of the problem. (B)
Cannulation of AVGs:
Grafts generally should not be cannulated for at least 2 weeks after placement and not until swelling has subsided so that palpation of the course of the graft can be performed. The composite PU graft should not be cannulated for at least 24 hours after placement and not until swelling has subsided so that palpation of the course of the graft can be performed. Rotation of cannulation sites is needed to avoid pseudoaneurysm formation. (SeeTable 4.) (B)
Dialysis catheters and port catheter systems:
Infection-control measures that should be used for all HD catheters and port catheter systems include the following:
The catheter exit site or port cannulation site should be examined for proper position of the catheter/port catheter system and absence of infection by experienced personnel at each HD session before opening and accessing the catheter/port catheter system. (B)
Changing the catheter exit-site dressing at each HD treatment, using either a transparent dressing or gauze and tape. (A)
Using aseptic technique to prevent contamination of the catheter or port catheter system, including the use of a surgical mask for staff and patient and clean gloves for all catheter or port catheter system connect, disconnect, and dressing procedures. (A)
There is considerable evidence that the use of maximal sterile precautions, as opposed to clean aseptic technique, for cannulation of AV accesses and catheter accession is both impractical and unnecessary.222-225 However, the importance of strict dialysis precautions226 and aseptic technique222 cannot be overemphasized in the prevention and minimization of all access infection.227 Despite the general acceptance of the importance of standard precautions for hand washing and glove changes, these simple acts to minimize transmission of disease frequently are skipped. An audit in a selection of Spanish HD units examined opportunities to wear gloves and wash hands per the standard preventive guidelines (high-risk activities of connection, disconnection, and contact between patients during dialysis). Gloves were worn by only 19% and hands were washed after patient contact on only 32% of all occasions.228 Mandatory hand washing before patient contact occurred only 3% of the time. A decade later, wearing of gloves improved to 92%, but the practice of hand washing before or after these patient-oriented procedures remained low at 36% after and 14% before such activities.229 Greater adherence was found in acute than in long-term HD units. A greater patient-nurse ratio independently influenced hand-washing rates. With the increasing microbial resistance to mainstream antibiotics,230 infection prevention must be considered the first rule of vascular access maintenance.231 Data from prospective studies in both Canada and the United States clearly show that great variability exists between centers in infection rates, indicating the need to have not only a national registry, but also a local (ie, in-center) infection surveillance program.232-234 Increased awareness at the individual center level is key to stemming access infection and its extreme consequences, such as endocarditis and metastatic infections (eg, spinal abscesses), conditions that are disabling at best, sometimes fatal, and prohibitively costly to treat.235,236
In the effort to prevent infection, it is not only staff that must be vigilant to potential breaks in technique and the need for the appropriate use of masks. Patients also must be taught that lapses in their use of masks and poor personal hygiene are known to increase their risk for infection. Patients with type 2 diabetes are at increased risk for nasal staphylococcal carriage and catheter-related bacteremia (CRB) as a result.237,238
Maturation and Cannulation of Fistulae (CPG 3.2)
If the fistula is created with both adequate inflow artery and outflow vein, the increased flow in the vein should be immediately apparent postoperatively, evidenced by larger appearance and the presence of a continuous audible and palpable thrill along the vein, as well as actual flow measurements.126 Experienced staff should examine the fistula and the outflow vein each time the patient comes to dialysis to monitor the maturation progress. Aspects of the physical examination are summarized in Table 5. The ability of “trained, experienced dialysis nurses” to accurately predict eventual fistula maturity is excellent.72 This is even more reason to have a protocol for regular clinical examination in place in dialysis centers to teach the skills of physical examination (see CPG 4 and CPG 5) to all staff members and assess the developing fistula and not focus on the access in current use only. The optimal time to do this examination is before fluid removal because hypotension can confound the findings. Patients who are not yet on dialysis therapy should be taught how to perform self-examination and be given appropriate contact information for questions and concerns. Poor prognostic signs, such as significant decrease in the thrill, should be referred immediately back to the surgeon or the interventionalist for prompt evaluation and intervention. At a minimum, all newly created fistulae must be physically examined by using a thorough systematic approach by a knowledgeable professional 4 to 6 weeks postoperatively to ensure appropriate maturation for cannulation.239 The steps for cannulation are summarized in Table 3.
Protocol for Initial Cannulation of AVFs
If the physical assessment has shown that the fistula is adequately matured, ideally, the next step is to perform a trial cannulation. In general, the earliest that this situation occurs is when the vein diameter is greater than 0.4 cm, has a flow greater than 500 mL/min,59 and at least 1 month has elapsed since fistula creation60 (Table 3). If possible, the trial cannulation of the fistula should be done on a nondialysis day. This serves to eliminate any potential complications associated with the administration of heparin.
If a trial cannulation is not possible, it is best to perform the initial cannulation of the new access at the patient’s midweek HD treatment. Performing the initial cannulation midweek helps avoid such complications as fluid overload and elevated chemistry test results associated with the weekends.
To ensure that the needle is placed properly, needle placement should be confirmed with a normal saline flush before connecting the needles to the blood pump and starting the pump. Blood return alone is not enough to show good needle placement. One option to easily check for proper needle placement is the use of “wet” needles. The needle is purged of air and the saline in the attached syringe is used to flush the needle. If an infiltration has occurred, the normal saline is less harmful to the surrounding AVF tissue. The wet needle also prevents the risk for a blood spray or spill if dry needles are used for cannulation and the caps are opened to “bleed out” the needle from the air. The opening of the needle is a risk for blood exposure to the dialysis team member, patient, and nearby patients. For these reasons, use of a wet needle is a safer technique for the AVF, patient, and dialysis team members, especially for the initial AVF cannulation. This option should be considered as part of the dialysis unit’s cannulation policy and procedures. The recommended procedure is described next.
Attach a 10-mL syringe filled with 8 mL of normal saline solution to the AVF needle, but do not prime the needle until immediately before the cannulation.
Grasp the fistula needle by the butterfly wings and prime the needle with normal saline until all the air is purged. Clamp the needle closed. Remove the protective cap and immediately proceed with the cannulation technique.
When the needle has advanced into the vessel, blood flashback will be visible (the needle may need to be unclamped to see the blood flashback) and, if visible, aspirate back 1 to 5 mL with the 10-mL syringe. Flush the needle with the normal saline solution and clamp. The syringe must aspirate and flush with ease. Monitor for signs or symptoms of infiltration. Patients usually experience immediate sharp pain upon infiltration of saline or blood into the tissues.
Needle selection for the initial cannulation is critical. One method used to select the appropriate needle size is a visual and tactile examination. This examination allows the cannulator to determine which needle gauge would be most appropriate, based on the size of the vessels in the fistula. Alternately, place 17 G and 16 G needles with the protective cap in place (prevents a needle stick) over the cannulation site. Compare the vein size with the needle size with and without the tourniquet applied. If the needle is larger than the vein with the tourniquet, it is too large and may infiltrate with cannulation. Use the needle size that is equal to or smaller than the vein (without the tourniquet) for the cannulation.
The smallest needle available, usually a 17 G, typically is used for initial cannulation attempts. It is important to keep in mind that blood flow delivered by a 17 G needle is limited. Prepump arterial monitoring is recommended to ensure that blood pump speed does not exceed that which the needle can provide. Prepump arterial pressure should not exceed −250 mm Hg. Based on performance of the fistula using a 17 G needle, the decision to increase the needle size for subsequent cannulation can be made.
A needle with a back eye should always be used for the arterial needle to maximize the flow from the access and reduce the need for flipping the needle.
Apply a tourniquet to the access arm.
After disinfecting the access site per unit protocol, carefully cannulate the fistula, using a 25° insertion angle.
When blood flash is observed, flatten the angle of the needle, parallel to the skin, and advance slowly. When the needle is in the vessel, remove the tourniquet and tape the needle securely per unit protocol.
Assess for adequate blood flow by alternately aspirating and flushing the needle with a syringe.
Assess carefully for signs of infiltration, ie, pain, swelling, or discoloration.
Repeat steps 1 to 5 for the second needle.
A fistula that only works with a tourniquet in place is still underdeveloped, usually because of inflow stenosis, and needs more time or reevaluation by the VAT before use.
The combined use of the new fistula and bridge vascular access (ie, TCC as a return for blood) may be necessary until the fistula is well developed.
Cannulation performed at a nonturnover time may provide more time for the cannulation procedure.
Infiltrations, Problems, and Tips
Infiltrations with the cannulation can occur before dialysis, during dialysis with the blood pump running, or after dialysis with the needle removal.
Monitor closely for signs and symptoms of infiltration. A quick response to a needle infiltration can help minimize damage to the access.
If the infiltration occurs after the administration of heparin, care must be taken to properly clot the needle tract and not the fistula. In some cases, the decision to leave the needle in place and cannulate another site may be appropriate. The immediate application of ice can help decrease the pain and size of the infiltration and may decrease bleeding time.
Use caution when taping needles. Avoid lifting up on the needle after it is in the vein. An improper needle flip or taping procedure can cause an infiltration.
If the fistula is infiltrated, it is best to rest the fistula for at least 1 treatment. If this is not possible, the next cannulation should be above the site of the infiltration. If the patient still has a catheter in place, restart use of the fistula with 1 needle and advance to 2 needles, larger needle size, and greater BFRs as the access allows.
Proper needle removal prevents postdialysis infiltrations. Apply the gauze dressing over the needle site, but do not apply pressure. Carefully remove the needle at approximately the same angle as it was inserted. This prevents dragging the needle across the patient’s skin. Using too steep of an angle during needle removal may cause the needle’s cutting edge to puncture the vein wall.
Do not apply pressure to the puncture site until the needle has been completely removed.
Fistula Hand-Arm Exercise (CPG 3.2.3)
Strengthening the forearm by using isometric exercises to increase handgrip strength (eg, squeezing a rubber ball with or without a lightly applied tourniquet) may increase blood flow, thereby enhancing vein maturation,240 and has been shown to significantly increase forearm vessel size,127,241 thereby potentially increasing flow through a fistula created using these vessels. The resulting muscle mass increase also may enhance vein prominence. Exercise also may decrease superficial fat. Correction of anemia also could increase cardiac output and decrease peripheral resistance, potentially resulting in increased flow through the fistula.
Access Flow for Dialysis in Fistulae (CPG 3.3)
After appropriate physical examination, a fistulogram is the gold standard for evaluating poor maturation of the fistula if the patient is already on dialysis therapy. Use of a non-nephrotoxic contrast material, carbon dioxide, or ultrasound should be used for patients not yet on dialysis therapy. Although a fistula can maintain patency at lower blood flows than grafts, thrombosis still occurs and, if not treated promptly, can lead to permanent loss of the access. Thrombosis rates can be reduced by prospective correction of problems.242 Delivery of dialysis is flow dependent: access flow less than 350 mL/min is likely to produce recirculation and inadequate delivery of dialysis. (See the HD Adequacy Guidelines.) Some centers have used diluted contrast (25%), and there are now published data that suggest this diluted contrast does not adversely impact residual kidney function.639 The images are of acceptable quality. The appropriate intervention for poor maturation is based on the cause of the dysfunction and may involve PTA of stenotic lesions, ligation or occlusion of vein branches (if the problem is simply > 1 major outflow vein),122,243 and/or surgical intervention, including revision of the anastomosis.75,125,126
Cannulation of AVGs (CPG 3.4)
Manufacturers’ guidelines are based on the time needed for tissue-to-graft incorporation, thereby preventing the possibility of a hematoma dissecting along the perigraft space. However, most patients experience significant tissue swelling as a result of the tunneling, and palpation of the graft is difficult for the cannulator and painful for the patient.
Placement of a graft that allows for early cannulation may be advantageous in the patient who needs to begin dialysis therapy, has no other access, and does not have veins suitable for a fistula. Such an access would preclude the necessity to place a catheter while a conventional graft matures. This type of graft confers no additional benefit beyond early cannulation.114,119,128
Biografts are more likely to become aneurysmal than PTFE grafts,116 and cannulation techniques should be a hybrid of the techniques for a graft regarding depth of the access and the texture of an autogenous vein. Rotation of cannulation sites should be observed in these grafts; however, constant cannulation (buttonhole) has not been studied.244
Dialysis Catheters and Port Catheter Systems (CPG 3.5)
A dislodged (cuff exposed) or potentially infected catheter or exit site requires further assessment and possibly an intervention before being deemed safe to access for dialysis.
The Centers for Disease Control and Prevention (CDC) has no preference between transparent dressing and gauze, except in the case in which the exit site is oozing, which requires gauze.222 Standard practice is to clean the exit site and redress at each dialysis treatment (see Table 6).
Airborne contaminants from both patients and staff are prevented best by the use of surgical masks when the catheter lumens or exit site are exposed. Wearing clean gloves and avoiding touching exposed surfaces further decreases the risk for infection. Aseptic technique includes minimizing the time that the catheter lumens or exit site are exposed.222,226 Manufacturers’ directions should be adhered to for the types of disinfectants recommended for safe cleaning of the skin and device. If not contraindicated, the CDC recommends use of 2% chlorhexidine,222 shown to be superior to povidone-iodine.245,246 Careful attention to hub care can decrease the CRB rate almost 4-fold to a rate approaching 1 episode/1,000 days.247
Many of the guidelines are based on good standards of clinical practice. Those relating to the use of “aseptic” technique follow the recommendations of the CDC. It is unlikely that randomized trials will ever be done in this area.
Establishing Constant-sites in Native Fistulae by Using Standard Sharp Fistula Needles
Perform a complete physical assessment of the fistula and document the findings.
Select the cannulation sites carefully. Consider straight areas, needle orientation, and ability of the patient to self-cannulate. Sites should be selected in an area without aneurysms and with a minimum of 2 inches between the tips of the needles.
Remove any scabs over the cannulation sites.
Disinfect the cannulation sites per facility protocol.
Using a sharp fistula needle, grasp the needle wings and remove the tip protector. Align the needle cannula, with the bevel facing up, over the cannulation site and pull the skin taut (Fig 1A).
Cannulate the site at a 25° angle; self-cannulators may require a steeper angle (Fig 1B). It is important to cannulate the developing constant-site access in exactly the same place, using the same insertion angle and depth of penetration each time.
Note: It takes approximately 6-10 cannulations using a sharp needle to create a scar tissue tunnel track. Arterial and venous sites may not develop at the same rate. Once a scar tissue tunnel track is well formed, the antistick dull bevel needles should be used. If standard sharp needles are used beyond the creation of the buttonhole sites, the scar tissue tunnel can be cut. More pressure and more needle manipulation will be required to advance the antistick needle down the tunnel track. This can lead to bleeding or oozing from the needle site during use on HD. The sharp needle can also puncture the vessel at a new site or cause an infiltration. The quick transition to the antistick needle will preserve the integrity of the buttonhole site and prevent complications.
This requires that a single cannulator perform all cannulations until the sites are well established.
Note: It takes approximately 6-10 cannulations using a sharp needle to create a scar tissue tunnel track. Arterial and venous sites may not develop at the same rate. Once a scar tissue tunnel track is well formed, the antistick dull bevel needles should be used. If standard sharp needles are used beyond the creation of the buttonhole sites, the scar tissue tunnel can be cut. More pressure and more needle manipulation will be required to advance the antistick needle down the tunnel track. This can lead to bleeding or oozing from the needle site during use on HD. The sharp needle can also puncture the vessel at a new site or cause an infiltration. The quick transition to the antistick needle will preserve the integrity of the buttonhole site and prevent complications.
A flashback of blood indicates the needle is in the access. Lower the angle of insertion. Continue to advance the needle into the fistula until it is appropriately positioned within the vessel (Fig 1C).
Securely tape the fistula needle (Fig 1D) and proceed with dialysis treatment per facility protocol.
Cannulating Mature Constant Sites in Native Fistulae Using an Antistick Dull Bevel
Perform a complete physical assessment of the fistula and document the findings.
Remove any scabs over the cannulation sites.
Disinfect the cannulation sites per facility protocol.
Using an antistick dull bevel, grasp the needle wings and remove the tip protector. Align the needle cannula, with the bevel facing up, over the cannulation site and pull the skin taut (Fig 2A) .
Note: Ensure that the same needle insertion angle and depth of penetration are used consistently for each cannulation of a constant site.
Note: Ensure that the same needle insertion angle and depth of penetration are used consistently for each cannulation of a constant site.
Carefully insert the needle into the established cannulation site (Fig 2B). Advance the needle along the scar tissue tunnel track. If mild to moderate resistance is met while attempting to insert the needle, rotate the needle as you advance it, using gentle pressure (Fig 2C).
A flashback of blood indicates when the needle is in the access. Lower the angle of insertion. Continue to advance the needle into the fistula until it is appropriately positioned within the vessel.
Securely tape the needle set (Fig 2D) and proceed with the dialysis treatment per facility protocol.
Guideline 4. Detection of access dysfunction: Monitoring, surveillance, and diagnostic testing
Prospective surveillance of fistulae and grafts for hemodynamically significant stenosis, when combined with correction of the anatomic stenosis, may improve patency rates and may decrease the incidence of thrombosis.
The Work Group recommends an organized monitoring/surveillance approach with regular assessment of clinical parameters of the AV access and HD adequacy. Data from the clinical assessment and HD adequacy measurements should be collected and maintained for each patient’s access and made available to all staff. The data should be tabulated and tracked within each HD center as part of a Quality Assurance (QA)/CQI program.
Physical examination (monitoring):
Physical examination should be used to detect dysfunction in fistulae and grafts at least monthly by a qualified individual. (B)
Surveillance of grafts:
Techniques, not mutually exclusive, that may be used in surveillance for stenosis in grafts include:
Intra-access flow by using 1 of several methods that are outlined inTable 7using sequential measurements with trend analysis. (A)
Directly measured or derived static venous dialysis pressure by 1 of several methods. (A) (Protocol provided inTable 8for using transducers on HD machines to measure directly; criteria inTable 9for derived methods.)
Duplex ultrasound. (A)
Physical findings of persistent swelling of the arm, presence of collateral veins, prolonged bleeding after needle withdrawal, or altered characteristics of pulse or thrill in a graft. (B)
Unstandardized dynamic venous pressures (DVPs) should not be used. (A)
Surveillance in fistulae:
Techniques, not mutually exclusive, that may be used in surveillance for stenosis in AVFs include:
Direct flow measurements. (A)
Physical findings of persistent swelling of the arm, presence of collateral veins, prolonged bleeding after needle withdrawal, or altered characteristics of pulse or thrill in the outflow vein. (B)
Duplex ultrasound. (A)
Recirculation using a non–urea-based dilutional method. (B)
Static pressures (B), direct or derived. (B)
When to refer for evaluation (diagnosis) and treatment:
One should not respond to a single isolated abnormal value. With all techniques, prospective trend analysis of the test parameter has greater power to detect dysfunction than isolated values alone. (A)
Persistent abnormalities in any of the monitoring or surveillance parameters should prompt referral for access imaging. (A)
An access flow rate less than 600 mL/min in grafts and less than 400 to 500 mL/min in fistulae. (A)
A venous segment static pressure (mean pressures) ratio greater than 0.5 in grafts or fistulae. (A)
An arterial segment static pressure ratio greater than 0.75 in grafts. (A)
The following terms will apply to HD vascular access
Monitoring—the examination and evaluation of the vascular access by means of physical examination to detect physical signs that suggest the presence of dysfunction.
Surveillance—the periodic evaluation of the vascular access by using tests that may involve special instrumentation and for which an abnormal test result suggests the presence of dysfunction.
Diagnostic testing—specialized testing that is prompted by some abnormality or other medical indication and that is undertaken to diagnose the cause of the vascular access dysfunction.
Purpose of Access Surveillance
Vascular access function and patency are essential for optimal management of HD patients. Low BFRs and loss of patency limit HD delivery, extend treatment times, and, in too many cases, result in underdialysis that leads to increased morbidity and mortality.248 Between 1991 and 2001, the incidence of vascular access events in patients undergoing HD increased by 22%.249 In long-term AV accesses, especially grafts, thrombosis is the leading cause of loss of vascular access patency. Thrombosis increases health care spending7,250 and adversely affects QOL,162,250-253 and vascular access–related complications account for 15% to 20% of hospitalizations among patients with CKD stage 5 undergoing HD.7,12,252 Prevention of access dysfunction by maintaining adequate flow and preventing thrombosis translates into a policy of “Dialysis Dose Protection.” (See the KDOQI HD Adequacy Guidelines.) It is not feasible for any one individual to manage all aspects of access care. Multidisciplinary teams should be formed at each HD center,254-256 with a VAT coordinator, if possible. Whatever the team’s size and composition, its most important function is to work proactively to ensure the patient is receiving an adequate dialysis dose by maintaining access function and patency.
The basic tenet for vascular access monitoring and surveillance is that stenoses develop over variable intervals in the great majority of vascular accesses and, if detected and corrected, underdialysis can be minimized or avoided (dialysis dose protection) and the rate of thrombosis can be reduced. Whether prospective monitoring and surveillance can prolong access survival currently is unproven. However, it fosters the ability to salvage vascular access sites through planning, coordination of effort, and elective corrective intervention, rather than urgent procedures or replacement.257 A number of monitoring and surveillance methods are available: sequential access flow, sequential dynamic or static pressures, recirculation measurements, and physical examination.
Failure to detect access dysfunction has consequences on morbidity and mortality.248,249 In a recent study of 721 randomly selected patients from all 22 long-term HD units in northeast Ohio, barriers found to significantly (P < 0.001) and independently relate to inadequate dialysis dose delivery were patient noncompliance, low dialysis prescription, catheter use, and access thrombosis.253 Every 0.1 decrease in Kt/V was independently and significantly (P < 0.05) associated with 11% more hospitalizations, 12% more hospital days, and a $940 increase in Medicare inpatient expenditures. Vascular access–related complications accounted for 24% of all hospital admissions.258 The reader is referred to the KDOQI HD Adequacy Guidelines for additional information on the importance of achieving the prescribed dialysis dose with regard to mortality.
Asymptomatic, but hemodynamically significant, stenoses usually are detected through a systematic monitoring and surveillance program. Detection of such stenoses is important to prevent progression to a functionally significant stenosis, currently defined as a decrease of greater than 50% of normal vessel diameter, accompanied by hemodynamic or clinical abnormality, such as abnormal recirculation values, elevated venous pressures, decreased blood flow, swollen extremity, unexplained reduction in Kt/V, or elevated negative arterial prepump pressures, that prevent increasing to acceptable blood flow.259 This definition evolves from an analysis of hemodynamics and clinical correlation.
Access flow and pressure are related in a permanent AV access through the relationship:
The driving force for access flow, QA, is the pressure gradient, ΔP, between the artery and central veins. This driving force tends to be the same for both fistulae and grafts. Within the constraints imposed by the arterial anastomotic site, the ultimate access flow in mature accesses tends to be similar in fistulae and grafts.260,261 What differs is the rate of maturation. Grafts reach their maximum flow rate in a matter of days to weeks, as opposed to fistulae, which may require weeks to months to mature.71,138,262-264 This difference in achieving maximum flow may explain the difference in the incidence of immediate steal between the 2 access types, with the fistulae permitting more time for adaptation to occur.
The pressure profile differs in the 2 access types. As shown in Fig 3, the pressure decrease profile in a graft progressively decreases along the length of the graft. At both anastomoses, there are pressure gradients, even in the absence of stenosis (illustrated as the luminal incursions). Within the body of the graft, there is a 20- to 30-mm ΔP that is the effective driving force.265-267
Conversely, in a fistula, the preponderance of the arterial pressure is dissipated within the first few centimeters of the access; pressures in the “arterial segment” are only approximately 20% of those in the feeding artery.265-267Fig 4 shows the difference in profiles.
The IAP ratio refers to the actual pressure at the site of measurement divided by the mean arterial blood pressure (MAP). The effective ΔP in the fistula generally is only 8 to 10 mm Hg, frequently 25%, and seldom more than half those noted in grafts. Despite these differences in pressure profiles, access flow in grafts and fistulae are approximately equal at 6 months267 because the overall ΔP is the same. However, fistulae—unlike grafts—have an intact endothelial lining that allows them to actively dilate and remodel over extended periods. As a result, progressive flow increases are limited only by cardiac factors. Fistulae also differ from grafts in having side branches that reduce resistance to flow (parallel circuits). However, multiple accessory veins can limit the development of the major superficial vein needed for cannulation (see CPGs 1 and 2). Ligation of accessories or spontaneous occlusion of side branches within a fistula results in an access that hemodynamically mimics the profile of a graft.
It is immediately apparent that 2 anatomic factors determine access function: (1) quality and (2) physical dimensions of the artery and vein. The major determinant of QA in a given patient will be determined by the capacity of the artery to dilate and its general “health.” In general, arteries at more distal sites have less capacity to deliver flow than more proximal sites, ie, radial < brachial < axillary < femoral. Arteries that are calcified or affected by atherosclerosis will result in lower flow accesses whether supplying a fistula or a graft. If the artery is healthy, flow capacity will be determined by the characteristics of the vein used in access construction. Too small a vein will limit the flow in both a fistula and graft. Unfortunately, arterial disease is not uncommon; access inflow stenosis occurs in one third of the patients referred to interventional facilities with clinical evidence of venous stenosis or thrombosis.268 This is much greater than has been traditionally reported.10,24,105,108,269 Thus, it is very important to assess the access by using physical examination early after its construction. Because flow and pressure measurements are not performed routinely until the access is cannulated, initial assessment of the access depends on the physical examination, which can detect many problems in a fistula.
Effect of Stenosis on Hemodynamics: Access Flow, IAP, Access Recirculation, and Physical Examination
In grafts, the majority of stenoses develop in the venous outflow, frequently right at or within several centimeters of the venous anastomosis.10,24,105,108 Lesions within the graft also occur, and most accesses have more than 1 lesion at any 1 time.10,266,267,269 The pathophysiological state of graft failure arises from neointimal hyperplasia. In a fistula, there may be ischemic effects, as well as injury resulting from recurrent cannulation and subsequent fibrosis. Stenoses in a fistula tend to occur at the surgical swing sites (including the arterial anastomosis) or the puncture zone of the vein. The outcome is the same in both fistulae and grafts: a reduction in access flow rate. However, the effect on IAP differs according to access type and site of stenosis. As illustrated in Fig 5, an outlet stenosis in a graft will increase the pressure at all locations upstream from the stenosis. Conversely, an inflow lesion will decrease all pressures downstream of the stenosis. An intragraft stenosis between the needles will decrease flow while increasing pressure upstream and decreasing pressure downstream of the lesion.
In a fistula, pressure profiles depend on the location of the lesion and the presence or absence of collateral or accessory veins. Arterial inflow lesions that develop after acceptable maturation are detected more easily by using QA, the inability to deliver blood flow to the dialyzer, reductions in adequacy, and recirculation measurements270,271 than by IAP measurements. Intra-access pressure (PIA) with inflow lesions tends to remain unchanged or decrease as QA decreases over time.272 An outflow lesion will produce a pressure profile similar to that seen in grafts; the magnitude of the pressure elevation is dictated by the number of venous tributaries. Not uncommonly, in upper-arm fistulae, there is spontaneous or deliberate occlusion of side branches (as with transposition); an outflow lesion then produces a pressure profile very similar to that of grafts.
For a given graft access, the access flow pressure profile resulting from venous outflow stenosis is illustrated in Fig 6.
An initially well-functioning graft with an access flow approaching 2 L/min (usually in the upper arm) will manifest decreasing flow as both the arterial and venous pressure slowly increase with the development of outflow tract stenosis. Hemodynamic simulations indicate that flow decreases by less than 20% until the stenosis process produces a 40% to 50% decrease in luminal diameter. Thereafter, flow decreases rapidly as the degree of stenosis increases to 80%.273 Because the intimal hyperplasia process progresses with time, its detection requires sequential measurements of flow or pressure or both to detect a threshold at which action should be taken. Note that the graft thrombosis region by flow shown in the hatched area is reached long before a graft would show recirculation and therefore affect the delivered dose of dialysis. Access recirculation in grafts is a late manifestation of stenosis and a poor predictor of imminent thrombosis; it occurs in less than 20% of cases.271 For this reason, the Work Group no longer recommends recirculation measurements in grafts. Conversely, because fistulae typically can maintain patency at much lower flows than grafts, recirculation occurs much more frequently; 1 study reported that about one third of fistulae had a significant recirculation fraction by using an ultrasound dilution technique.271 When recirculation was measured by using the Fresenius Body Thermal Monitor (BTM), the device was able to detect fistulae requiring revision with a sensitivity of 81.8% and specificity of 98.6%, although the BTM method does not differentiate between access and cardiopulmonary recirculation.274
The main issue for most HD clinics is which surveillance test best meets their needs. The following discussion summarizes the methods available and the reason for the ordering of the test by the Work Group in CPGs 4.2 and 4.3.
Physical Examination (Look, Touch, Listen)
Physical examination can be used as a monitoring tool to exclude low flows associated with impending graft failures.275,276 There are 3 components to the access examination: inspection (look), palpation (touch), and auscultation (listen).276 The Work Group is convinced that the basic skills have been largely abandoned in favor of technology and need to be taught to all individuals who perform HD procedures.277 Simple inspection can reveal the presence of aneurysms. A fistula that does not at least partially collapse with arm elevation is likely to have an outflow stenosis. This logic applies to the case in which a tourniquet does not appear necessary for optimal cannulation. Strictures can be palpated and the intensity and character of the bruits can suggest the location of stenosis. Downstream stenosis also produces an overall dilation of the vein, giving it “aneurysmal” proportions.
In grafts, one can determine the direction of flow in a loop configuration and avoid inadvertent recirculation by erroneous needle insertion. In a patent graft in which blood flow is less than the blood pump flow setting, the presence of recirculation can be detected easily by occluding the graft between the needles and looking at the arterial and venous pressures. A strong pulse too often is misinterpreted as being evidence of good flow, rather than the opposite. A pulse suggests lower flows.278 In a newly thrombosed graft, the arterial pulse often is transmitted into the proximal end of the graft, leading to erroneous cannulation, which could be avoided easily by simply using a stethoscope to confirm absence of flow. A bruit over an access system and its draining veins that is only systolic is always abnormal; it should be continuous. An intensification of bruit suggests a stricture or stenosis.278 Palpable thrill at the arterial, middle, and venous segments of the graft predicts flows greater than 450 mL/min.278 A palpable thrill in the axilla correlates with a flow of at least 500 mL/min.279 The character of pulse and thrill correlates with postintervention outcome for stenosis.280 The interested reader is referred to additional literature for further enjoyment and enlightenment.271
Of note, a preliminary study has shown that sounds acquired by using electronic stethoscopes that were then digitized and analyzed on a personal computer could be used to characterize stenoses.281 Stenotic vessel changes were found to be associated with changes in acoustic amplitude and/or spectral energy distribution. Acoustic parameters correlated well (r = 0.98; P < 0.0001) with change in degree of stenosis, suggesting that stenosis severity may be predicted from these parameters. Furthermore, acoustic parameters appeared to be sensitive to modest diameter changes of 20%. These results suggest that, in the future, readily available computerized analysis of vascular sounds may be useful in vessel patency surveillance.
Access flow can be measured by using a number of techniques, as summarized in Table 7. Doppler ultrasound (DU)282-287 and MRA46,54,288-290 are direct techniques for assessing flow in vascular accesses. Duplex Doppler ultrasound (DDU) requires an accurate measurement of the cross-sectional diameter of the access. The method is operator dependent and subject to error caused by variation in cross-sectional area and the angle of insonation.291,292 Because turbulence in the access can limit the accuracy of the measurements, flow measurements can be made in the feeding artery (usually the brachial) or distal part of the access.272 The difference between the flow in the artery and the access usually is less than 10%. Despite these operator-related and equipment-related limitations, sequential measurements have been used extensively to detect and refer patients for interventions or predict the risk for thrombosis. In addition to flow measurements, both DDU and MRA provide anatomic assessment and direct evidence for the presence, location, and severity of access stenosis. However, the current cost of these methods, as well as the inability to make measurements during HD, limits their use. Research and development are needed to simplify procedures and reduce costs.
Indirect methods use an indicator dilution technique; the major techniques include ultrasound dilution (UDT),272,293 a timed ultrafiltration method294; transcutaneous access flow rate (TQA), a method that can be performed during or independently of HD295,296; glucose infusion297,298; differential conductivity299,300; and, finally, ionic dialysance.301,302 All the methods described, except for TQA, variable flow DU, and glucose infusion, require measurements with the blood tubing initially in the normal position and then reversed to induce access recirculation.
With UDT, access flow is measured from the induced recirculation when the needles are reversed. The software calculates the area under the curves (AUC) as a measure of recirculation.
where QBP is blood pump flow and R is degree of recirculation induced. The UDT method is the only one that independently measures actual flow in the tubings, rather than accepting the readings on the HD system for the roller pump.
Pitfalls in measurement have been identified and recently reviewed.303 Accurate calibration of the blood pump is essential with most methods, but frequently is not performed regularly. The indicator injection also must not affect flow in the access itself. The technique must separate access recirculation from cardiopulmonary recirculation that is unavailable with high-efficiency dialysis. Finally, access flow is a function of the ratio of systemic to access resistance, and measurements should be conducted within the first 90 minutes of dialysis to minimize effects of hypotension. Table 10 summarizes the recommendations for access flow surveillance. All methods require some modification/interruption of the dialysis treatment, except perhaps ionic dialysance.
With ionic dialysance, alteration of the proportioning ratio of dialysate to water alters the dialysis sodium concentration, as well as blood sodium level. The resulting change in blood sodium level, as well as the change in dialysate conductivity, serves as the indicator for calculating QA.
where D is the dialysance in the normal blood tubing position and Dr is the value with the tubing reversed. As with UDT, ultrafiltration should be minimized and recirculation must be absent in the normal blood tubing configuration. At flow rates less than 1,000 mL/min, the method consistently underestimates access flow compared with UDT.301,302
With the timed ultrafiltration method, a difference in hematocrit (Hct) is the indicator
where Qf is ultrafiltration rate, H0 is initial Hct, and ΔH is change in Hct induced by ultrafiltration with the tubing in reversed (r) and normal (n) positions. The method correlates well with UDT.
The TQA method has not been extensively used.
The variable-flow DU method304-306 measures velocity between the 2 dialysis needles at varying dialyzer blood flows. Using a conservation of volume approach, a computer algorithm solves for access flow without the need to measure the cross-sectional diameter of the access.306 The method’s accuracy is best at flows less than 1,000 mL/min.
The easy availability of urea as a marker has led some to use it as an indicator substance to calculate recirculation and therefore derive flow. Such measurements underestimate flow compared with conductivity.307 Although QA can be estimated by using the urea method, the sensitivity and specificity of a low value is a poor predictor of access outcome and may lead to cost-ineffective investigations.307
Variation in access flow during dialysis308 can result from changes with cardiac output,309-311 MAP,309,310 and changes in blood volume.311 Access flow can increase by up to 11% or decrease by up to 30% from initial values by the end of dialysis, potentially impairing the ability of QA to predict impending vascular access failure.312 Access resistance remains stable during treatments and could be a more useful measure of vascular access performance as part of an access surveillance program. For all these reasons, it is recommended that measurements be made early in the HD treatment.
Measurements of pressure from the HD circuit were not originally designed to assess access (dys)function, either directly or indirectly. Rather, they were used to calculate the mean transmembrane pressure so that the appropriate ultrafiltration rate could be achieved. Volumetric control systems made these measurements unnecessary. Pressure measurements were retained to provide safety. During HD, blood is drawn out of the vascular access through the arterial needle by the blood pump on the HD machine.
Prepump pressures are now used to determine whether the prescribed dialyzer blood flow can be delivered without generating excessive negative pressures. At high negative pressures, the collapse of the pump segment reduces the true flow and true flow may differ from “displayed” flow by up to 15%.313,314 The degree of collapse is affected, in turn, by differences among manufacturer tubing sets.315 These considerations are important in evaluating the relationship of flow to access pressure. Excessively negative pressures can result in hemolysis.316 Differences in blood tubing performance are of obvious importance to manufacturers, leading to improvements. The newer generations available may show little differences with the improved blood flow delivered during dialysis, benefiting all patients.
When blood passes through the dialyzer, the blood traverses the venous drip chamber and returns to the patient’s vascular access though the venous needle. The pressure required to infuse blood back into the access is recorded as the venous drip chamber pressure (VDP) or DVP. The original purpose of VDP was to detect infiltration or malpositioning of the needle because partial occlusion of the needle orifice or infiltration would quickly increase and sound an alarm. There still is no “alarm” for detecting accidental withdrawal of the needle outside the body; exsanguinations have occurred.
One of the components of the VDP is the actual IAP (PIA). As shown in Fig 4, the IAP (PIA) in a graft is usually less than 50% of MAP. Most of this pressure decrease occurs at the arterial anastomosis, unless there is intragraft stenosis. When outflow stenosis develops (eg, because of neointimal hyperplasia at or downstream from the graft-vein anastomosis), PIA increases and flow decreases. When PIA increases to greater than 50% of MAP (PIA/MAP greater than 0.50), graft flow commonly has decreased into the thrombosis-prone range of 600 to 800 mL/min (Fig 6), and the presence of stenosis is likely. If a stenosis develops in the body of a graft between the areas used for arterial and venous limb cannulation, PIA at the venous needle remains normal or can even decrease despite increasing stenosis.270,271 Stenosis at the arterial anastomosis of both grafts and fistulae causes PIA to decrease. Conversely, a high basal PIA can be observed with a healthy artery in the absence of stenosis when the flow delivered is in excess of the venous system’s initial capacity. Because of these pressure confounders, there is little correlation between a single measurement of flow and PIA/MAP.317 Serial measurements of pressure in each patient are more valuable than isolated measurements of either PIA or PIA/MAP ratio. This is illustrated in Fig 7. Note that the arterial pressure ratio is approximately 0.2 units higher than the venous ratio and the baseline initial value for both ratios is lower than usual because of the use of a 4- to 6-cm taper at the arterial anastomosis that limits inflow to prevent steal.
In fistulae, blood entering the venous system returns through multiple collateral veins. As a consequence, PIA/MAP in a fistula is, on average, less than in a graft and may not increase with outlet stenosis. The test, therefore, theoretically is less valuable as a surveillance tool for stenosis in fistulae. However, most elbow-level fistulae do not have or lose collaterals and often behave hemodynamically like grafts. In both fistula types, elevation of PIA/MAP indicates the development of a stenosis in the venous outflow from the access and is associated with an increased probability of access failure or need for revision to provide adequate blood flow for HD.10,265,266,317
Like access flow, measurement of PIA has evolved.
Direct measurement of static pressure
Pressures in the access can be measured directly at the site of cannulation in the “arterial” and “venous” segments of the graft or fistula by using a pressure-measuring device. Although one can use a sophisticated electronic method (separate transducers placed in line with the dialysis tubing)265-267 as originally reported, a much simpler technique uses a device consisting of a hydrophobic Luer-Lok connector that connects a standard dialysis needle to an aneroid manometer.318
IAPs also can be measured by using the pressure transducers of the dialysis machine. Under conditions of no blood flow and no ultrafiltration, the only difference between the pressure measured by an independent transducer and the machine transducer is that resulting from the height differential between the location of the machine transducers and the access. The two pressures can be equated by either moving the access to the level of the venous drip chamber or moving the drip chamber to the level of the access. Alternatively, the height difference, Δh, can be measured and the additional pressure (0.76 · Δh) can be added to the machine transducer reading.319
Table 8 provides the sequence of steps for measuring static pressure. It is important that the pressure transducers be calibrated accurately.
Venous outlet stenosis can be detected with venous PIA alone. Trend analysis is more useful than any single measurement. The greater the degree of stenosis at the outlet, the greater the venous pressure ratio. Strictures between the area of arterial and needle cannulation cannot be detected by measuring venous (PIA) pressure alone.271 Detection of these lesions requires simultaneous measurement of pressures from both the arterial and venous needles. Central stenoses that have collateral circulation may have “normal” pressures, but these usually present with significant ipsilateral edema. Accesses can be classified into the categories listed in Table 9. Using the equivalent PIA ratios from the arterial or venous needles, the criteria must be met on each of 2 consecutive weeks to have a high likelihood of a 50% diameter lesion.
Patients who develop a progressive and reproducible increase in venous or arterial segment greater than 0.25 units more than their previous baseline, irrespective of access type, also are likely to have a hemodynamically significant lesion. Intra-access strictures usually are characterized by the development of a difference between the arterial and venous pressure ratios greater than 0.5 in grafts or greater than 0.3 in native fistulae. Because fistulae can remain patent at much lower flows than grafts, sequential measurement of conductance (ie, a blood pump/absolute value of prepump pressure), particularly at maximum prepump pressure permitted by the system, can detect fistula dysfunction and stenosis.320,321
Although measuring static pressure as described in Table 8 is straightforward, it is tedious, time consuming, and not “user friendly.” Staff frequently bypass crucial steps, leading to poor-quality data being collected and recorded. This has led to a reevaluation of statistical methods to use the information within the dynamic pressure.
VDP or DVP and extraction of equivalent PIA
DVP (also referred to as VDP under conditions of blood flow) is measured routinely during HD in the presence of extracorporeal blood flow. These pressures can be read off the dialysis machine or stored electronically with the blood pump running. One of the components of DVP is the actual IAP (PIA) because the pressure needed to return blood into the access is the sum of that needed to overcome the needle resistance and IAP. DVP/VDP has been used to detect venous outlet problems,322 but measurements are meaningful only if obtained at the beginning of dialysis and usually with low BFRs (50 to 225 mL/min) because at high BFRs, much of the resistance to flow is from the needle, and not the vascular access.
Measurement of DVP is less sensitive and specific than direct measurements of access flow rates or static pressure measurements. The reason for “poorer” performance results from many factors, including the lack of consistency about which flow should be the standard, varying in studies from 50 to 425 mL/min322-325; differences in needle design (wall thickness, actual length); and effects of viscosity affected chiefly by Hct. In addition, use of DVP as a method also requires that studies be performed to standardize the critical value as a function of needle gauge, length, and inner diameter (wall thickness). Consistency requires that a uniform flow value to test at be determined.
Indirect methods for determining PIA
Most HD systems can store the blood pump values associated with DVP. A computerized algorithm has been developed that uses an empirical formula to calculate an equivalent PIA from the DVP made during treatment. During a given treatment, many measurements at different flows can be made along with the simultaneous MAP, and an average equivalent PIA/MAP can be calculated. The average values can be trended with each treatment and examined for an upward trend. When the ratio exceeds 0.55, the access has a greater risk for clotting.326 This technique has been commercialized, providing monthly reports and trend analysis. Its ability to predict thrombosis is equal to that of direct measurement of PIA. In the evolution of the IAP ratio to detect stenosis, the discriminator value has progressively increased from 0.4 using the ratio of systolic pressures, 0.45 using the ratio of mean pressures measured directly, 0.5 using transducers on the machine, and finally 0.55 when deriving PIA from the dynamic pressure.
Recirculation: Method, Limits, Evaluation, and Follow-Up
Recirculation is the return of dialyzed blood to the dialyzer without equilibration with the systemic arterial circulation. The technique is not recommended as a surveillance tests in grafts. However, up to one third of dysfunctional fistulae will show an increase in recirculation that may be manifested as a decrease in urea reduction ratio (URR) or Kt/V, but this occurs late.
Access recirculation in a properly cannulated access is a sign of low access blood flow192 and a marker for the presence of vascular access stenosis, particularly in fistulae. Such stenoses can be corrected, preventing underdialysis and decreasing the risk for access thrombosis.327 Access recirculation can be measured accurately by using UDT328 or conductivity.299 A K+-dilution method is more reliable than the 2-needle urea-based method and compared with UDT, has 100% sensitivity, 95% specificity, 91% positive predictive value, and 100% negative predictive value.329 In analogy to access flow measurement, glucose infusion also has been used to measure recirculation.330
The amount of recirculation occurring with reversed needles usually is substantial (>20%), as confirmed when the tubings are deliberately reversed for access flow measurements. However, even with ideal sample timing and proper cannulation, laboratory variability in urea-based measurement methods will produce variability in calculated recirculation.331 Therefore, individual recirculation values less than 10% by using urea-based methods may be clinically unimportant. The Work Group believes that they do not prompt further evaluation. Values greater than 10% by using urea-based recirculation measurement methods require investigation.
New loop grafts are at particular risk for reversed needle placement because of a lack of familiarity with the access anatomy. When possible, an access diagram that depicts the arterial and venous limbs should be obtained from the surgeon who constructed the access to aid in proper cannulation. If not available, the anatomy can be deduced by temporarily occluding the graft at its midportion. The portion retaining a pulse is the arterial limb.
Comparison of Surveillance Methods
Accuracy and Reproducibility
Only 1 study has directly compared many of the available flow techniques with regard to reproducibility.332 Reproducibility is assessed by using duplicate measurement at unchanged conditions, whereas accuracy is determined under controlled change in a relevant measurement condition (2 different blood flows for ultrasound, changed sensor position in TQA). An accurate method produces the same result. In most studies using some form of dilution or concentration of an indicator, UDT is taken as the reference method for comparison because it most accurately separates cardiopulmonary from access recirculation and independently measures blood flow to the dialyzer. Ultrasonic flow is approximately 10% to 15% less than indicated by the blood roller pump, the magnitude correlating inversely with negative arterial blood tubing pressure.333 It shows very high reproducibility, for measurement at the same extra corporeal blood flow, QB (correlation coefficient of duplicate measurement, r = 0.97; n = 58) and measurement at 2 different QB (r = 0.97; n = 24), justifying its current status of a reference method in QA evaluation.334 The coefficient of variation usually is less than 8%.327 Slightly lower reproducibility is found with thermal dilution (TD) or Fresenius BTM at the same QB (r = 0.92; n = 40) and 2 different QB (r = 0.851; n =168); this inaccuracy can be overcome by increasing the number of measurements with averaging. Use of the simple Krivitski formula, QA = QBP (1/R − 1) in TD (which measures total recirculation, ie, sum of access recirculation and cardiopulmonary recirculation) brings about underestimation of QA, which progressively increases from QA of about 600 mL/min upward. High correlation of TD versus UDT (r = 0.95; n = 54) makes TD a viable clinical alternative in QA evaluation. Consistently different QA values obtained at 2 different QBs should prompt closer investigation of anatomic conditions of the access. Good correlation (r = 0.87; n = 27) also is found between QA measured by using DDU and UDT.332,335
The direct TQA method showed very high reproducibility (r = 0.97; n = 85); however, only for unchanged sensor position. Correlation of QA measured at 2 different sensor positions was much worse (r = 0.73; n = 22). Correspondence of TQA with UDT was satisfactory (r = 0.81; n = 36). Skilled and experienced operators are a must with this method. Similar results were found by others who reported, for triplicate measurements, coefficients of variation of 7.5% for differential conductivity by hemodynamic monitoring (HDM), 9.1% for UDT, and 17.4% for optodilution by ultrafiltration (OABF).336 Repeatability data (variation among temporally separated measurements) showed values of 10.6% for HDM, 13.0% for UDT, and 25.2% for OABF. Fewer comparisons have been made with the other methods. Glucose pump test (GPT) flow measurements correlate well with UDT measurements and have acceptable replicability.298
Ionic dialysance or conductivity dialysance, as it frequently is referred to, is being used increasingly by clinicians to measure access flow in both the United States and Europe, particularly with Fresenius dialysis delivery systems, in which the methodology is built into the machines as on-line clearance. Major refinements have been made to increase the replicability and accuracy of this method at lower BFRs, but preliminary reports comparing the measurements with UDT have not yet been formally published.
Detection of Stenosis or Predicting Thrombosis
As important as accuracy of a method is, the goal of any surveillance method is to detect access stenosis in a timely way so that appropriate correction can be undertaken before thrombosis. A hemodynamically significant stenosis is the substrate for thrombosis by reducing flow, increasing turbulence, and increasing platelet activation and residence time against the vessel wall.
Table 11 summarizes the available studies in which the presence and degree of stenosis was confirmed by using angiography. As reflected by data in the table, DDU is most accurate because it can directly visualize the degree of stenosis. When DDU is used to measure flow, rather than identify anatomic stenosis, sensitivity and specificity decrease. A quick survey of the table clearly shows that none of the tests consistently achieves a sensitivity of 90% and specificity greater than 80%.
Because of the accuracy of DDU in detecting the presence of a 50% (by diameter) stenosis,337 it has been used in some studies as the reference method, rather than angiography, to avoid invasive procedures. As shown in Table 12, UDT has good accuracy, whereas physical examination has high specificity, but poor sensitivity.
Table 13 shows that DDU and UDT are equivalent in predicting thrombosis.
Data are still limited for some of the newer surveillance tests. Table 14 summarizes the observations. There is excellent correlation between flow measurements by means of GPT and UDT (r > 0.9).298 GPT also has been validated recently as a surveillance technique in grafts. Using DDU to assess for the presence of stenosis, GPT picked up severe stenosis in 14 of 112 grafts (100% sensitivity) and performed better than UDT (86% sensitivity).297 Specificity was less than 60% for both tests. Diagnostic efficiency (percentage of grafts with agreement between test result and factual situation) was 90% and 80% (P = 0.056) for GPT and UDT, respectively. MRA also can provide anatomic338 and QA measurements, but it is prohibitively expensive. Intravascular ultrasounds (IVUSs) can be used to evaluate abnormalities in fistulae297 and may find abnormalities not seen with angiography. However, it is too expensive for routine use, but may be a valuable adjunct in evaluating the efficacy or completeness of the intervention on the access.
An important issue in fistulae is the assessment of such abnormalities as aneurysms and extreme tortuosity in “well-functioning” fistulae. DU is a very valuable technique, particularly in fistulae; in addition to measuring flow and identifying stenosis directly, it can detect other abnormalities in presumably well-functioning accesses.345 Pseudoaneurysms do not decrease access flow; QA is significantly greater than the mean (1,204 mL/min) in fistulae with aneurysms, calcifications, and tortuous vessels and, of course, less in those with stenosis. No correlation is noted between QA or the presence of stenosis with fistula age. Some degree of stenosis was detected in 64% of fistulae, with 57% of stenoses located in the anastomotic region; 22%, in the vein junction; 19%, at 1 or both ends of the aneurysm; and 2%, in the remaining region of the efferent vein.345 Chronic venous occlusion with collateral veins was detected in 6% of fistulae.345 Aneurysms were observed in 54% of fistulae with a mean diameter of 12.4 mm, with 96% of them located at puncture sites. Ten patients had a small thrombus in an aneurysm and at puncture sites. Thus, although a high level of abnormalities is present in well-functioning mature fistulae, the abnormalities are not sufficient to affect the functioning of the HD fistula and, in most cases, need only observation. More advanced lesions require therapy (see CPG 5).
DDU is a particularly useful modality to determine reasons for maturation failure of fistulae 4 to 12 weeks after construction,346 even if preoperative vein mapping had shown adequate vein size (≥3 mm) and outflow. Using the criteria of peak systolic velocity ratio (SVR) of 2:1 or greater to detect a 50% or greater stenosis involving arterial inflow, and venous outflow and an SVR of 3:1 or greater to detect a 50% or greater anastomotic stenosis, DDU of 54 native fistulae (23 brachiocephalic, 14 radiocephalic, and 17 basilic vein transpositions) found that 20% were occluded and 26% were normal. The remainder showed a variety of lesions: 16 fistulae (42%), venous outflow; 13 fistulae (34%), anastomotic; and 2 fistulae (5%), inflow stenoses. In 7 fistulae (18%), branch steal with reduced flow was found. Sensitivity, specificity, and accuracy of DDU in detecting stenoses of 50% or greater were 93%, 94%, and 97% compared with fistulography, respectively. Because many of these fistulae cannot be studied by using other surveillance techniques, routine DDU surveillance of primary fistulae should be considered to identify and refer for correction of flow-limiting stenoses that may compromise the long-term patency and use of the fistula.
Inflow stenosis is more common than previously believed (ie, <5% of cases). An inflow stenosis is defined as stenosis within the arterial system, artery-graft anastomosis (graft cases), artery-vein anastomosis (fistula cases), or juxta-anastomotic region (the first 2 cm downstream from the arterial anastomosis) with a 50% or greater reduction in luminal diameter judged by comparison with either the adjacent vessel or graft. Such stenosis was found in nearly a third of 223 cases referred to an interventional facility serving several centers.268 All referred accesses had a coexisting stenosis on the venous side. The frequency of inflow stenosis was less in grafts (29% of cases) than fistulae (40 of 101; 40%). Of these, 22 (54%) had a coexisting lesion on the venous side. Access inflow stenosis thus is much greater than traditionally reported in cases referred to interventional facilities with clinical evidence of venous stenosis or thrombosis.
Attempts to combine the various surveillance techniques have been performed. One study found no difference in the ability to detect stenoses in grafts from using QA by UDT compared with static venous pressure ratios.340 However, DVPs were of little use. Use of a PIA compared with QA also was examined in 125 grafts followed up for 80.5 patient-years.347 Standardized monitoring of either PIA, QA, or the combination of both, followed by subsequent corrective intervention, decreased the thrombosis rate in grafts compared with a historical control rate.348 Rates in 2 separate parts of the study for thrombosis not preceded by a positive test result were 0.24 and 0.32 episodes/patient-year at risk compared wth a historical rate greater than 0.7, respectively. The surveillance strategies were equally effective in decreasing thrombosis rates, and access survival curves were not significantly different between subgroups.347 Again, DVP alone was not useful because either QA or PIA turned positive before the dynamic pressure limit (>150 mm Hg at 200 mL/min) was reached. Unlike these 2 studies showing limited to no utility of DVP alone, another study was able to find some utility for DVP measurements for grafts.349 Stenosis greater than 50% by diameter on fistulography or a thrombotic event was defined as a “vascular access impairment episode,” whereas stenosis less than 50% or the absence of a thrombotic event was defined as “no vascular access impairment episode.” By combined dynamic pressure readings and flow surveillance (DVP > 120 mm Hg; QA < 500 mL/min in fistulae and < 650 mL/min in grafts or a decrease in QA > 25% compared with the highest previously measured value were considered positive), improved sensitivity over flow alone for fistulae, but not grafts, was observed.268 Sensitivity and specificity of the combined surveillance protocol for fistulae were 73.3% and 91%; in grafts, they were 68.8% and 87.5%, respectively. The rate of thrombotic events was less in patients with fistulae who underwent early repair, but in grafts, the addition of DVP did not decrease the thrombosis rate any further than surveillance based on QA alone. Finally, when UDT, DDU flow, DVP, and prepump pressure were examined as predictors of thrombosis in 172 grafts, DVP used alone was not predictive.285
In summary, available data suggest that the utility of DVP at flows of 150 to 225 mL/min to predict stenosis or thrombosis is limited or absent in grafts. Studies are needed to determine whether the method retains any utility in fistulae. Conversely, flow measurements, DDU assessment for stenosis, and static pressure measurements (direct or indirect by using computers) can detect hemodynamically significant stenosis in grafts and fistulae. Although the location of stenosis in fistulae (inflow) favors QA over PIA, no direct comparisons have been made by using DDU anatomic imaging or contrast angiography to determine the accuracy of the techniques in this access type. If the prescribed Kt/V is not delivered in a patient who is using a fistula, measurement of access flow should be performed by using a recommended method (Table 7).
The Work Group believes there is insufficient evidence to suggest 1 surveillance technique from those listed in the guidelines as “preferred or acceptable” because the choice at a particular site is affected by many variables; chief among these are access type, technology, effect of operator, and cost (usually labor). Although DDU studies are predictive of access stenosis and the likelihood for failure,350 frequency of measurement is limited by expense. In addition, interobserver variability in measurement of DDU flow in some instances can reduce the reliability of DDU flow measurement.351 Variation in the internal software used for calculating DDU flow measurements by different manufacturers also is a factor preventing standardization. Magnetic resonance flow is accurate, but expensive. Both DDU flow and magnetic resonance are difficult to perform during HD sessions.
Conversely, flow measurements performed by using UDT and other techniques can be done on-line during HD, thereby providing rapid feedback. The same applies for PIA. Both access flow and IAP techniques have been validated in prospective observational studies.10,322,347,349,352,353 Measuring static venous pressures is the least expensive method of surveillance for stenosis.322,354 Because of efficiency or cost, these methods are listed as preferred. In-line access flow measurements (DDU) are available and have been improved in terms of accuracy and replicability. However, there are no data yet on efficacy in detecting stenosis or effect on thrombosis rate.
The Work Group believes that recirculation is a relatively late predictor of access dysfunction and, if used, has a minor role in fistulae only. Non–urea-based recirculation measurements are very accurate, but require specialized devices.
Unexplained decreases in delivered dialysis dose, measured by using Kt/V or URR, frequently are associated with venous outflow stenoses.355 However, many other factors influence Kt/V and URR, making them less sensitive and less specific for detecting access dysfunction. Inadequate delivery of dialysis dose is more likely to occur with a fistula than a graft.
In primary fistulae, inadequate flow through the access is the main functional defect predictive of thrombosis and access failure (defined as thrombosis or failure to provide adequate dialysis dose). Indirect measures of flow, such as dynamic and static venous dialysis pressure, may be less predictive of thrombosis and access failure in fistulae compared with grafts. However, measurement of recirculation becomes a more useful screening tool in fistulae compared with grafts because flow in fistulae, unlike grafts, can decrease to a level less than the prescribed blood pump flow (ie, <300 to 500 mL/min) while still maintaining access patency.192,270,271 DDU may be useful in fistulae.346 Comparative studies using HDM (QA, PIA) and DDU need to be performed before firm recommendations can be made by the Work Group.
Regular assessment of physical findings (monitoring) may supplement and enhance an organized surveillance program to detect access dysfunction. Specific findings predictive of venous stenoses include edema of the access extremity, prolonged postvenipuncture bleeding (in the absence of excessive anticoagulation), failure of the vein to collapse with arm elevation, and changes in physical characteristics of the pulse or thrill in the graft.108,354 Physical examination is a useful screening tool to exclude low flow (<450 mL/min) in grafts with impending failure.275,277,278 In the context of proper needle position, an elevated negative arterial prepump pressure that prevents increasing the BFR to the prescribed level also is predictive of arterial inflow stenoses.
When a test indicates the likely presence of a stenosis, angiography should be used to definitively establish the presence and degree of stenosis. Currently, the Work Group is in agreement with the Society for Interventional Radiology, which recommends angioplasty if the stenosis is greater than 50% by diameter. Angioplasty by its very nature is a “disruptive” force on the vessel and can injure endothelium and underlying smooth muscle; each angioplasty can produce benefit or harm. However, there have been no large-scale trials to determine whether correction of only “hemodynamically” significant lesions (those associated with “low” access flows or “high” pressures or a change in access flow or pressure) is superior to correction of all stenosis greater than 50%. At the time of intervention, hemodynamic evaluation of each stenosis generally is not carried out.
Until such studies are conducted, the Work Group believes that the value of routine use of any technique for detecting anatomic stenosis alone—without concomitant measurement of access flow, venous pressure, recirculation, or other physiological parameters—has not been established. Stenotic lesions should not be repaired merely because they are present. If such correction is performed, then intraprocedural studies of QA or PIA before and after PTA should be conducted to show a functional improvement with a “successful” PTA.
The Patient as His or Her Own Surveyor and Protector
The Work Group strongly advocates that all patients should be taught the “basics” of how to take care of their vascular access, including steps in personal hygiene, cleanliness, avoidance of scab picking, and so on, as discussed in Table 15. In addition, patients should be taught where and how to detect a “pulse,” where and how to feel for a thrill, how to recognize infection, and—most importantly—when to notify a member of the dialysis staff of physician when the pulse or thrill is absent. Delay in recognizing loss of patency may influence the likelihood of restoring patency.
The patient must be taught the reason for avoiding “1-site-itis.” Topical anesthetics should be used judiciously if they help the patient comply with the policy of rotation of needle sites. To avoid aneurysm formation, the patient should insist on site rotation unless a buttonhole method is being used in a native fistula. With the large staff turnover ratios prevalent in HD units in the United States, the patient must be diligent that staff uses the proper aseptic techniques whenever the access is palpated, inspected, or cannulated.
Surveillance and Thrombosis
In dialysis AVGs, thrombotic events result primarily, but not solely, from progressive venous outflow stenosis.10,24,105,300,354,356-358 Thrombotic events that cannot be resolved (ie, patency restored) are the leading cause of access loss. These stenoses are caused by intimal and fibromuscular hyperplasia in the venous outflow tract, typically at the graft venous anastomosis,359-362 but can occur in the body of the graft, as well. The details of pathophysiology are beyond the limits of this discourse except to state that, to date, promising therapies in animal models have not yielded success in humans. Possible future therapeutic approaches have been summarized.363
As stenoses increase in severity, they produce a resistance to flow, increasing PIA with an accompanying decrease in blood flow.266,318 Cross-sectional studies using DDU or UDT showed a progressive increase in risk for access thrombosis during a follow-up interval of 1 to 6 months. The absolute value of the “critical or threshold” QA depends on the method used. Average access flow rates obtained by DDU are less (600 to 900 mL/min)252,335,364 than those measured by using magnetic inductance (mean, 1,100 mL/min) or UDT (mean range, 900 to 1,200 mL/min).336 Studies also showed that when access flow is measured repeatedly, trends of decreasing flow add predictive power for the detection of access stenosis or thrombosis.284-286,300,311,318,349,364-371 Grafts with access blood flows less than 600 to 800 mL/min have a greater rate of access thrombosis than grafts with flow rates greater than 800 mL/min.268,284,286,300,311,318,372 In addition to this absolute value, a decrease of 25% in access flow from a previous “stable” baseline greater than 1,000 mL/min has been suggested as a criterion for further diagnostic evaluation of grafts to detect the presence of at least one 50% (by diameter) stenosis within the access.285,364,369-371 In general, the interval that is present to correct the lesion in grafts before the access thromboses varies inversely with the access flow, being less than 8 weeks at a flow less than 450 mL/min371 and 3 months at flow rates of 600 to 800 mL/min.285
Although many centers refer patients directly for angiographic study without intermediate studies when a critical value is obtained, there may be a role for DDU anatomic scanning.282 Because fistulae maintain patency at lower flows than grafts, criteria for intervention in fistulae are not as well established. Values of 400 to 650 mL/min have been proposed. Higher values increase sensitivity, but lose specificity. Some fistulae can maintain patency for years at flows less than 400 mL/min, but with high-efficiency/high-flux dialysis, the treatment time requires extension. Conversely, intervention with PTA almost invariably triggers a process of repeated need for PTA because the frequency of at least 1 abnormality in an access is so high. Optimal care of a particular patient requires individualization, and not rigid application of protocols.
Because the development and severity of stenosis evolve to varying degrees among patients over time, the likelihood of detecting a hemodynamically significant stenosis increases if the surveillance test is repeated frequently. Therefore, surveillance should be performed at intervals of 1 month or less—depending on the complexity and cost—to detect access dysfunction early and permit sufficient lead time for intervention. The Work Group concluded that trend analysis could be as important as any individual value for any monitoring technique. Because access pressure measurements do not require complex technology, their frequency should be greater than that for access flow measurements. For direct measurement of access pressure, a frequency of twice a month appears sufficient. With methods more likely to produce variation under real-world clinical practice conditions (such as those from the HD system transducers), measurements once every 1 to 2 weeks are needed to detect a trend. The Work Group believes that measurement of static pressures every 2 weeks is the minimum frequency that is compatible with current HD staffing patterns. Derived static pressures need analysis from all available treatments for the month. Dynamic pressures should not be performed in grafts.
Measurement of access flow also was shown to be a valuable tool in determining the success of a therapeutic intervention. Failure to increase access flow by at least 20% after an intervention reflects failure of the intervention to correct the underlying problem.282,369 In 1 study, values before PTA and ΔQA correlated with the subsequent decrease in QA (P < 0.005).282 It was observed that QA increased after PTA (from 371 mL/min to 670 mL/min in a total of 65 grafts and 33 fistulae), but in a substantial percentage of cases, not to levels greater than 600 mL/min. QA values before PTA and the increase in QA values correlated with long-term outcomes, whereas angiographic results did not. Unfortunately, in many of the studies, the literature has admixed results for flow and outcome for both fistula and graft, making it impossible to sort out effects in grafts as opposed to fistulae. The Work Group believes there may be important differences in the response of fistulae (compared with grafts) to PTA, and surgical approaches also may influence outcomes. Research is needed in this area.
A large number of studies that used historical control data showed that prospective surveillance/monitoring to detect stenosis reduces the rate of thrombosis, although at the expense of increased procedures.10,322,343,373,374 A seminal study showed that a prospective program of dynamic pressure surveillance could detect stenotic lesions, reduce thrombosis rates, and reduce access replacement rates.322 In that study, fistulae and grafts were not differentiated with respect to efficiency of the test. Unfortunately, criteria developed with needles designed for low-efficiency dialysis (16 G; pressure > 150 mm Hg at a flow of 200 mL/min) were not adapted for larger bore needles (15 G and 14 G), and other investigators did not independently standardize their pressure criteria for the flow actually used (150 to 225 mL/min). Accordingly, results of this study generally were not duplicated.340 Until such standardization is performed, DVP alone is not recommended. Additional studies using static pressure,10 physical examination alone,352,353 DVP combined with access recirculation plus physical finding,373 DDU,284,374 and QA341,366,369,375 all showed a 41% to 67% reduction in thrombosis rate in grafts. A review suggested that the effect may be smaller in fistulae.374
Receiver operating characteristic (ROC) curve analyses have been performed to assess the overall performance of access flow and pressure in predicting thrombosis. Although in some studies, a good AUC of 0.84 to 0.9 was achieved for access flow, overall AUC for 10 studies was only 0.7.376 Addition of a change in flow increased AUC slightly to 0.82, but not to the value of 0.9 that an excellent test would produce (90% sensitive and 80% specific).377 The sum of QA and ΔQA did not perform any better than PIA/MAP.
Unfortunately, the high baseline rate of thrombosis in grafts precludes a sensitive test that can unequivocally predict the likelihood of thrombosis or not over a specified time. During a 3-month observation period, grafts can clot in the absence of any stenosis and do so at flows equal to those that remain patent, 1,209 versus 1,121 mL/min.270 In these cases, PIA remains unchanged. Grafts that required intervention or that thrombosed because of an anatomic lesion had much lower access flows, 656 mL/min and 609 mL/min, respectively. At flows greater than the threshold, the incidence of thrombosis may be as high as 20% per 6-month period.375 Even with flows in the highest quartile, greater than 1,395 mL/min, another study found a thrombosis rate of 9% during a period of 3 months (annualized risk, 36%).285 Until more studies are performed that examine the frequency of thrombosis in the absence of stenosis and the frequency of patency in the presence of arterial or venous stenosis, the debate will go on.378-381
At the present time, the development of a surveillance abnormality should be correlated with other findings on physical examination and adequacy of HD. Any abnormality (QA, PIA) must be confirmed before further referral for either DDU (stenosis characterization) or angiography.
Randomized Trials of Preemptive PTA in Response to Surveillance
To date, only a small number of studies have been performed prospectively to assess the impact of surveillance on outcome. These are summarized in Table 16.
The concept that prophylactic or preemptive PTA would decrease graft thrombosis initially was refuted.382 In a study of 64 patients identified to have a 50% stenosis by using DDU and confirmed by using angiography, preemptive PTA produced no change in 6-month or 12-month patency. Because of confounding issues, a subanalysis was performed on 21 “virgin” grafts that had not previously clotted or required intervention.383 Preemptive PTA from the time of diagnosis of stenosis reduced the thrombosis rate from 0.44 to 0.10 episodes/patient-year at risk. Both rates were much less than the rate of 0.91 in patients without virgin grafts. However, sample size was small (n = 19). It should be noted that in this study, only anatomic assessment was obtained; no hemodynamic assessment was performed.
The small number of patients in this and all other prospective studies has limited assessment of efficacy. One prospective study using PIA was performed.384 Although the study itself was well designed, it was flawed by the surveillance technique. A preliminary study was performed in which monthly static venous pressure measurements were made during 2 consecutive HD sessions in all patients with a functioning upper-extremity graft in 2 HD units during a 16-month period. The method for deriving PIA ratio differed significantly from that originally described10 in that the ratio of systolic PIA pressure to MAP was calculated instead of the ratio of systolic PIA pressure/systolic blood pressure.385 The net effect of this error is that the ratio would have been falsely elevated and the threshold value of 0.4 would not apply. In addition, measurements were performed less frequently than recommended. Not surprisingly, ROC analysis yielded curves with areas less than 0.64.383 Subsequently, 64 patients with “elevated static venous pressure” measured in an upper-extremity graft were randomized to intervention (underwent angiography and repair of identified stenoses) or observation (underwent stenosis repair only in the event of access thrombosis or clinical evidence of access dysfunction), with the primary end point being access abandonment. Information on the fraction in the interventional group who had a stenosis is not provided. There was no difference in access abandonment (14 patients in each group) during the 3.5-year study period or in time to access abandonment. However, the proportion of patients with a thrombotic event was greater in the observation group (72%) than the intervention group (44%; P = 0.04), but overall thrombosis rates were similar in the groups (ie, there was a difference in mean number of thrombosis per graft in the intervention group in grafts that did thrombose). Not detailed was the number of PTAs that had to be performed in both groups during the entire study period.
Two randomized studies examined the role of access surveillance by using QA. In the first, it was found that stenotic lesions are detected more commonly by using QA (QA < 650 mL/min or 20% decrease in QA) than “routine surveillance” (physical examination plus DVP > 150 mm Hg) in a total of 112 patients, but elective PTA for lesions greater than 50% did not alter thrombosis rate.386 Rates of graft loss, times to graft loss, and overall thrombosis rates did not differ between the 2 groups. However, interventions increased by 30% in the intervention group. In the second study, 101 patients were randomized to 3 groups: control, low surveillance QA (Transonics) monthly, or stenosis detection by using DDU quarterly.387 Referral for angiogram was based on clinical characteristics in all, less than 600 mL/min in QA, and greater than 50% diameter in the DDU stenosis groups. QA was measured in all 3 groups, but only used for referral in the flow surveillance group. Baseline thrombosis rates were 0.7 and 0.9/patient-year in the control and QA groups, respectively. Results showed that QA increased PTA rate marginally (from 0.22 to 0.33/patient-year) and had no effect on thrombosis rate. Stenosis surveillance increased PTA to 0.65/patient-year and reduced thrombosis rates to 0.5/patient-year, but did not affect 2-year survival rate. QA less than 600 mL/min was found in 4 of 18, 4 of 31, and 3 of 11 in the control, QA, and stenosis groups in grafts that clotted (overall, 11 of 60). However, 26 of 35 in the stenosis group underwent PTA for “stenosis.” In both studies, 20% to 25% of accesses clotted without a surveillance abnormality, ie, in a totally unexpected manner.
However, the overriding conclusion of the studies that surveillance using QA and PTA in response to a threshold value of QA did not alter graft survival has to be tempered by the small sample size of the studies, the comparator used, and the efficacy of the intervention. Graft survival studies require a sample size of approximately 700 patients to detect an increase in graft survival of 1 year or a 33% difference in survival by 3 years (H. Feldman, personal communication). None of the studies had 20% of this number. It also is important to assess the skill level of the staff. If the staff can reach a positive predictive value of 80% (when stenosis is present and needs intervention) through use of physical examination and clinical characteristics (monitoring), use of a surveillance method that has a sensitivity of only 80% will produce no benefit over good monitoring. Determining which lesions should undergo correction has already been addressed. Elastic recoil needs to be assessed.
In contrast to grafts, the role of QA surveillance appears to be more established in fistulae. In 1 study, the positive predictive value, negative predictive value, sensitivity, and specificity of ultrafiltration method for vascular access stenosis (OABF CritLine III) were 84.2%, 93.5%, 84.2%, and 93.5%, respectively. Vascular access thrombosis rates in 50 QA surveillance patients were less (2 of 50 patients; 4%) than in 94 patients not followed up with flow measurements (16 of 94 patients; 17%; P = 0.024).242
In a second study, a 5-year RCT of blood flow surveillance and preemptive repair of subclinical stenoses (1 or both of angioplasty and open surgery) with standard monitoring and intervention based upon clinical criteria alone was carried out in Italy.388 Surveillance with blood pump flow (QB) monitoring during HD sessions and quarterly QA or recirculation measurements identified 79 fistulae with angiographically proven significant (>50% diameter) stenosis that were then randomized to either a control group (intervention done in response to a decrease in delivered dialysis dose or thrombosis; n = 36) or preemptive treatment group (n = 43). Kaplan-Meier analysis showed that preemptive treatment decreased the failure rate (P = 0.003) and the Cox hazards model identified treatment (P = 0.009) and greater baseline QA (P = 0.001) as the only variables associated with favorable outcome. Access survival was significantly greater in preemptively treated than control fistulae (P = 0.050), with greater postintervention QA as the only variable associated with improved access longevity (P = 0.044). This study provides evidence that active blood flow surveillance and preemptive repair of subclinical stenosis reduce the thrombosis rate and prolong the functional life of mature forearm fistulae and that QA greater than 350 mL/min before intervention portends a superior outcome with preemptive action in fistulae.
Finally, in a third study, a prospective controlled open trial to evaluate whether prophylactic PTA of stenosis not associated with access dysfunction improves survival in native virgin radiocephalic forearm fistulae, 62 stenotic functioning fistulae (ie, able to provide adequate dose of dialysis) were enrolled: 30 were allocated to control, and 32, to PTA.389 Kaplan-Meier analysis showed that PTA improved fistula functional failure-free survival rates (P = 0.012) with a 4-fold increase in median survival and a 2.87-fold decrease in risk for failure. A Cox proportional hazards model identified PTA as the only variable associated with outcome (P = 0.012). It was found that PTA increased QA by 323 mL/min (P < 0.001), suggesting that improved fistula survival is the result of increased access flow. PTA also was associated with a significant decrease in access-related morbidity, halving the risk for hospitalization, central venous catheterization, and thrombectomy (P < 0.05). Because prophylactic PTA of stenosis in functioning forearm fistulae improves access survival and decreases access-related morbidity, it supports the use of a surveillance program for the early detection of these stenoses.
At present, a vascular surveillance program to identify patients who may benefit from angiography and PTA appears to offer the most likelihood of benefit and may reduce thrombosis rates. However, we need additional studies to examine the characteristics of stenoses that produce incomplete responses to PTA so that patients are adequately treated at the time of their interventions.
Guideline 5. Treatment of fistula complications
Appropriate interventions for access dysfunction may result in an increased duration of survival of the AVF.
Problems developing in the early period after AVF construction (first 6 months) should be promptly addressed.
Persistent swelling of the hand or arm should be expeditiously evaluated and the underlying pathology should be corrected. (B)
A program should be in place to detect early access dysfunction, particularly delays in maturation. The patient should be evaluated no later than 6 weeks after access placement. (B)
Intervention on a fistula should be performed for the presence of:
Inadequate flow to support the prescribed dialysis blood flow. (B)
Hemodynamically significant venous stenosis. (B)
Aneurysm formation in a primary fistula. Postaneurysmal stenosis that drives aneurysm also should be corrected. The aneurysmal segment should not be cannulated. (B)
Ischemia in the access arm (B).
Indications for preemptive PTA:
A fistula with a greater than 50% stenosis in either the venous outflow or arterial inflow, in conjunction with clinical or physiological abnormalities, should be treated with PTA or surgical revision. (B)
Abnormalities include reduction in flow, increase in static pressures, access recirculation preempting adequate delivery of dialysis, or abnormal physical findings. (B)
Stenosis, as well as the clinical parameters used to detect it, should return to within acceptable limits following intervention. (B)
Thrombectomy of a fistula should be attempted as early as possible after thrombosis is detected, but can be successful even after several days. (B)
Access evaluation for ischemia:
Patients with an AVF should be assessed on a regular basis for possible ischemia. (B)
Patients with new findings of ischemia should be referred to a vascular access surgeon emergently. (B)
Infections of primary AVFs are rare and should be treated as subacute bacterial endocarditis with 6 weeks of antibiotic therapy. Fistula surgical excision should be performed in cases of septic emboli. (B)
Initial Problems (CPG 5.1)
Minor swelling normally is found postoperatively after placement of an AVF regardless of location and type of anastomosis. This “physiological” swelling disappears within the first week. Swelling of the hand or area of the fistula should be treated with hand elevation and patient reassurance. Because prevention is always preferable to therapy, a major aspect of preventing postoperative swelling is to rest the arm. Persistent swelling requires further attention to exclude major outflow obstruction. Hematoma, infection, and venous hypertension also should be excluded by clinical examination277,391,392; noninvasive ultrasound examination helps confirm extravasations and hematomas or purulent infiltrations, as well as strictures/stenoses of the venous outflow tract.45,124,393 Although angiography (fistulography) can show a venous stenosis causing venous hypertension, DDU is the preferred diagnostic method because it avoids any diagnostic cannulation of the newly created AVF and thereby avoids iatrogenic damage of the thin wall of the freshly arterialized vein. If a stenosis is found, it should be treated with a balloon angioplasty.
Persistent hand edema usually follows a side-to-side anastomosis for creating the fistula and invariably results from downstream stenosis forcing the flow through venous collaterals. This process can produce classic chronic venostasis with skin ulceration. The lesion should be treated early by ligation of the tributaries. If delayed healing of the wound is noted in patients, the surgical technique should be examined closely. The surgical technique to close the skin preferably should use degradable suture material in an exclusively subcutaneous position supported by externally applied sterile adhesive strips to minimize the thickness of the scar.
Risk for bleeding and hematoma formation is greatest in the early stages of use of a fistula and greater in brachiobasilic fistulae than other types of fistulae at the wrist or elbow.77 Manifestations of an infiltration or hematoma aside from the obvious discoloration and swelling include the presence of high-frequency bruit on auscultation and a difference in intravascular pressure on palpation.277,391,392 Because hematoma may lead to access loss,77 hematomas should be treated surgically if they are compromising the lumen of the arterialized vein (producing stenosis).388 In the absence of luminal compromise by physical examination or DDU, the access should be rested until the margins of the fistula are again well demarcated.
Proficiency in cannulating fistulae is suboptimal in the United States despite considerable efforts to remedy the situation.120,394-396 One can improve needle design to minimize trauma397 and develop methods to increase the efficiency of buttonhole development,398 but it is for naught if the fistula cannot be cannulated consistently without infiltrations. Because an inability to “be sure of the location” of the 2 lateral borders of the fistula contributes to miscannulation (particularly in those who are obese or have deep fistulae) and is manifested by so-called clot aspiration and because DDU is very precise in depicting the borders of vessels (see CPG 1),344,399,400 patients should be referred for access mapping and photography. A useful procedure is for the ultrasonographer to draw a map on the surface of the skin with a washable marker directly over the center of the lumen (or the 2 lateral borders), make a digital photo map of the fistula based on ultrasound, and send the photograph of the usable portion of the fistula access to the dialysis center. Alternatively, the access can be marked with indelible ink that permits the establishment of a series of subsequent successful puncture sites to demarcate the center of the vessels if the rotating-site system of cannulation is used (see CPG 3). These techniques both educate the staff and develop expertise and confidence. In addition, they should foster greater expertise in assessing fistulae during the first postoperative weeks for delayed maturation. Prospective studies are needed to demonstrate this opinion-based strategy.
The majority of fistula creations can be performed on an outpatient basis. A crucial element is the postoperative examination and surveillance follow-up that is scheduled by either the surgeon or a vascular access coordinator representing the interdisciplinary VAT. The primary purpose is to detect problems of maturation (see CPG 2). Although a variety of factors can produce maturation failure,86,123,125 a greater than 70% successful fistula access rate can be achieved, even among patients who have diabetes86,87,401,402 and women.84 In a multiple logistic regression analysis of 148 grafts (60% forearm, 40% elbow), predictive factors of early failure were distal location (adjusted odds ratio [aOR], 8.21; 95% confidence interval [CI], 2.63 to 25.63; P < 0.001), female sex (aOR, 4.04; 95% CI, 1.44 to 11.30; P = 0.008), level of surgical expertise (aOR, 3.97; 95% CI, 1.39 to 11.32; P = 0.010), and diabetes mellitus (aOR, 3.19; 95% CI, 1.17 to 8.71; P = 0.024).403 Much of the prevention of delayed fistula maturation must occur preoperatively (see CPG 1) through appropriate selection of arterial and venous vessels, as well as procedures most suitable for the individual patient. Although it is the vein that must dilate and accept higher flows, the artery must be healthy too. The resistive index of the artery used to construct the fistula is a strong predictor of early primary HD fistula failure.404 However, despite selection of the best available artery and vein, maturation failure can still occur. By combining venous diameter (>0.4 cm) and flow volume (>500 mL/min) during DDU evaluation within the first 4 months after access construction, one can predict the likelihood of maturing a fistula,72 ie, one that can be cannulated and provides sufficient blood flow for dialysis, with 95% certainty (19 of 20 fistulae). Women were less likely to have an adequate fistula diameter of 0.4 cm or greater: 40% (12 of 30) compared with 69% for men (27 of 39). However, of note, the accuracy of experienced dialysis nurses in predicting eventual fistula maturity was excellent at 80% (24 of 30).72 This is more reason to have a protocol for regular clinical examination in place in dialysis centers to teach the skills of physical examination (see CPG 4) to all staff members and assess the developing fistula and not focus on only the access in current use. A new fistula should be monitored regularly during the postoperative 4 to 6 weeks for swelling, hematoma, infiltration, wound healing, and failure to mature.
Intervention (CPG 5.2)
A primary fistula should be revised when it is unable to sustain adequate HD blood flow, manifested by the inability to achieve the prescribed Kt/V within a reasonable HD duration. Low access blood flow has a major effect on the delivery of dialysis: inadequate blood flow may result in inadequate dialysis, thereby increasing patient mortality and morbidity.405,406 Impaired flow in fistulae is caused by impaired arterial inflow related to the site of cannulation. Location of the anatomic reason varies between arterial and venous lesions, as well as lesions within the anastomotic area.
Arterioatherosclerotic narrowing of the feeding artery with reduced flow and stenosis of the artery are found in an increasing portion of the elderly, patients with hypertension, and patients with diabetes. Therefore, careful preoperative evaluation should document data on anatomic and functional status of the arterial vasculature, including flow in the brachial artery (see CPG 1).
As stated, peripheral location of first fistula, female sex, diabetes mellitus, and, finally, surgical expertise are the main predictive factors of early fistula failure.72 Because it is known that arterial calcification in patients with diabetes is more pronounced in the wrist than elbow region,407 selection of a more proximally located site for creation of the AV anastomosis, eg, the proximal radial or beginning brachial artery in the proximal forearm, may be the better alternative. Inadequate flow in the area of the AV anastomosis is produced primarily by surgical factors. Two studies403,408 emphatically stressed that the early failure rate of fistula may be 3-fold greater when constructed by “occasionally” working access surgeons compared with experienced surgeons.
However, an initially adequate artery may become inadequate in time. Four of 40 patients had brachial artery lesions contributing to access dysfunction.409 In a larger series, 41 of 101 fistulae had arterial inflow lesions at the time of therapeutic intervention for dysfunction.268
In case of reduced flow caused by arterial inflow, 2 therapeutic options exist: stenosis of the feeding artery may require interventional angioplasty or surgical revision, or inadequate quality of the feeding artery (caused, eg, by calcification) may require a more proximally located new AV anastomosis. Although chronic arterial lesions in upper limbs bearing vascular access devices for HD most often manifest themselves as insufficient flow for HD treatment, the process may be severe enough to produce thrombosis and ischemia. For correcting stenoses, PTA is a safe and effective technique with a low rate of reintervention.268
Juxta-anastomotic venous stenosis is a commonly observed lesion. It occurs from the change in hemodynamic flow character from the artery into the vein and from devascularization of the venous wall during exposure, even after excellent surgery. Placement of the “arterial needle” downstream of this stenosis obviously supports the phenomenon of impaired flow. At times, it may be impossible to traverse the AV anastomosis by using the retrograde approach, and antegrade puncture of the brachial artery will be needed.410 Although interventional procedures are successful with this type of lesion,411 construction of a new AV anastomosis (revision) at a more proximal location is the preferred procedure.112 However, the therapeutic strategy depends on the type of lesion and variability of local expertise.
Hemodynamically Significant Venous Stenosis
The commonly used parameter to characterize the hemodynamic relevance of a stenosis is a reduction in vessel diameter exceeding 50% based on angiographic and/or ultrasonographic findings. In contrast to an exact diagnosis in a synthetic AVG with a known standard diameter, it may be difficult to describe reliably the percentage of narrowing in a native vein, particularly because this vein may present a prestenotic and/or poststenotic aneurysmic enlargement. The hemodynamic relevance of a 50% stenosis in a native AVF therefore should be supported by clinical symptoms, abnormal physical findings, and flow measurements (see CPG 4). The diagnosis of “hemodynamically relevant venous stenosis” based on a combination of clinical and technical findings should initiate a corrective procedure, either percutaneous or surgical intervention.
In AVFs, significant stenoses may not elevate dynamic or static pressures, although such lesions can result in decreased access flow and elevated recirculation (see CPG 4) that are associated with increased risk for thrombosis.369 Treatment of hemodynamically significant venous stenosis prolongs the use-life of the AVF.322,356,358,369,412 A study of 32 patients and 30 controls showed a beneficial effect on AVF survival of prophylactic angioplasty of stenoses.390 Subsequent Kaplan-Meier analysis of a larger cohort of patients over 5 years showed that preemptive treatment decreased the failure rate (P = 0.003), and the Cox hazards model identified treatment (P = 0.009) and greater baseline access flow (P = 0.001) as the only variables associated with favorable outcome.389 A significant increase in access blood flow rate was observed, as well as a significant decrease in access-related morbidity by approximately halving the risk for hospitalization, central venous catheterization, and thrombectomy. This group showed, in a population of 120 patients with AVFs, that UDT measurements were reproducible and highly accurate in detecting stenosis and predicting thrombosis in forearm AVFs. Neither QA/MAP nor ΔQA improved the diagnostic performance of QA alone, although its combination with ΔQA increased the test’s sensitivity for stenosis.339 These data support the value of monitoring and surveillance in AVFs (see CPG 4). In AVFs, 75% of stenoses producing low flow are at or near the AV anastomosis and 25% are in the outflow track.
Aneurysm Formation in a Primary Fistula
Progressive enlargement of an aneurysm eventually can compromise the skin above the fistula, leading to possible rupture. This can result in hemorrhage, exsanguination, and death. In the Work Group’s opinion, large aneurysms can prevent access to the adjacent fistula for needle placement, thereby limiting potential cannulation areas.
Aneurysm formation in a primary fistula can be observed in the following situations:
Within the first postanastomotic venous segment in the presence of a hemodynamically relevant stenosis in the juxta-anastomotic position. The therapy of choice is a new AV anastomosis using a “healthy” venous segment located a few centimeters more proximally, but as close to the former anastomosis as possible, to preserve the maximum area for cannulation. Here, surgery may provide better results than angioplasty. Secondary patency rates may be very similar, although repeated angioplasty is far more expensive, with increased morbidity, risk for catheter placement, and inadequate HD sessions.
Within cannulation areas. This type of aneurysm is caused mainly by the so-called “1-site-itis” cannulation413 and should lead to abandonment of the area for cannulation (see CPG 3) and strict enforcement of the “rope-ladder” cannulation method if a buttonhole does not seem practical. The latter is by far the best available method for prevention. For hemodynamic reasons, aneurysms of this type are combined at times with a preaneurysm stenosis, but more commonly with a postaneurysm stenosis.
Therapeutic options for managing the aneurysms include the following:
Cannulation should not be continued along any type of venous aneurysm, particularly in patients for whom the skin layer within the aneurysm is thin and prone to infection—a sign of impending perforation.
In cases of progression of aneurysm and stenosis, a series of surgical procedures are available, including: i) partial resection of the wall of the aneurysm and insertion of the resected material as patch along the stenosis, forming a patch from a segment of a venous branch; ii) mobilizing an adjacent venous branch for local repair by a “swing-by-technique”; and iii) other options. In all cases in which surgery can provide a (nearly) perfect inner diameter while preserving cannulation sites, angioplasty should be the second choice. Currently, stent insertion should be avoided along cannulation sites in fistulae.
Aneurysms along the venous outflow tract where cannulations are not performed routinely are found for anatomic reasons (eg, in junctions of veins, areas of venous valves with a rigid basic ring, and cases of old venous lesions caused by former venotomy, catheter insertion, and so on) as nucleus for a stenosis followed by a prestenotic aneurysm. Sometimes these lesions are caused by “1-site-itis,” in which the same area is cannulated repeatedly without any attempt at buttonhole development. It is particularly prone to develop when intra-AVF pressures are high, as in arm AVFs with cephalic arch stenosis, or in high-flow AVFs. The therapy of choice for these stenoses is angioplasty; when elastic recoil occurs, PTA should be combined with stent insertion in these more central outflow veins. Recurrent stenoses should undergo surgery.
Indications for Preemptive PTA (CPG 5.3)
Preemptive PTA may be indicated in certain cases of abnormal physical findings (see Fig 8). These findings are more important than other criteria. See also the rationale for CPG 5.2. However, certain facets should be kept in mind. This may be particularly important in “underserved” areas where the dialysis staff has no choice other than to rely on abnormal physical findings.
Tools for physical examination have been described in CPG 4. However, Table 17 provides a quick summary.
To detect the early beginning of an abnormality requires continuous meticulous education and daily practice. When a high level of expertise is achieved, a definitive diagnosis can be achieved in approximately 60% to 80% of cases through the presence of abnormal physical findings that lead to an intervention. These findings should be documented and preserved in the chart and—if possible—electronically to continue the observation of the very earliest abnormality. In the remaining 20% to 40% of patients without a definitive diagnosis after physical examination, further diagnostic steps should be undertaken using (preferably first) ultrasound followed by, if necessary, angiographic techniques, including the option of angioplasty during the same session; however, this is dependent on local availability and expertise.
Previous Thrombosis in the Access
It was shown repeatedly that thrombosis of AVFs is caused by anastomotic disorders, predominantly stenosis. Episodes of hypotension during HD may be contributory in some cases. No data exist to determine whether hypotension alone, even if for a few hours, can produce thrombosis in the absence of an underlying stenosis limiting flow into the access. Irrespective of type of treatment given for the previous episode(s) of access thrombosis, these patients should be considered at risk because anastomotic residuals or recurrent development of stenosis at the same site are common. Therefore, special attention should be taken to prevent recurrence of clinical signs. This strategy requires repeated continuous physical examination—a quick chairside procedure in the hands of experienced personnel preceding any cannulation procedure.
Persistent Abnormal Surveillance Test (see CPG 4.2)
Because surveillance test results at times are observer dependent, an abnormal isolated finding in any case should be supported by abnormal physical symptoms. Persistence of abnormal physical findings and surveillance test results (elevated pressures, low flows, abnormal recirculation) require that further diagnostic steps be initiated to establish an exact diagnosis and lead to timely treatment (see CPG 4).
Stenosis (CPG 5.4)
In the absence of method errors, repeated failure to deliver the prescribed dialysis dose by using an AVF should result in immediate evaluation of the vascular access when other reasons can be excluded, eg, technical errors, timing errors, and so on. (See the Guidelines for HD Adequacy and also the rationales for CPG 5.1 and CPG 5.2.)
The degree of stenosis is graded by the percentage of narrowing of the access, the reference being the diameter of the immediately upstream or downstream “normal vessel.” The reference diameter can be difficult to determine when the AVF is irregular or aneurysmal or at the confluence of 2 vessels. Grading of severity also can be done on the basis of the drop-off in systolic or mean pressure across the stenosis.414,415 The degree of residual effacement tolerated varies among interventionalists. Some demand no residual at all unless it is the first PTA ever done. Swelling, local or generalized in the arm, caused by central venous stenosis may take additional time to resolve.
Dilation often is painful locally and local anesthesia may be needed at times. Venous stenosis in the outflow may be “rock hard” and require high-pressure balloons (bursting pressures of 25 to 30 atmospheres), as well as more prolonged inflation periods. Resistant stenoses are less common, usually less than 1% in forearm and 5% of upper-arm fistulae.112 There is no convincing proof that such lesions respond better to cutting ballons416 because studies have been small and not prospective. The Work Group recommends that high-pressure balloons be used first because cutting devices have not been studied adequately.
Thrombectomy (CPG 5.5)
In most patients, thrombosis is the final complication after a period of AVF dysfunction. Treatment of thrombosis should start as early as possible. The risk of delay is progressive growth of the thrombus that makes interventional/surgical procedures more difficult and risky with regard to long-term success. The vascular access should be reopened as soon as possible to resume regular dialysis treatment and avoid resorting to a short-term catheter. In addition, delay produces a longer period of contact between the surface of the thrombus and the vessel wall, thereby increasing the risk that extraction of thrombus may further damage the endoluminal layer. This could favor future thrombotic events. Early intervention increases the likelihood that the same AVF can be used to provide future dialyses.
Although thrombectomy procedures are more challenging in fistulae than grafts, results are more rewarding.417 Better long-term patency has been achieved in the largest series to date as long as the underlying stenoses are sufficiently dilated: 1-year primary patency rates of 50% and secondary patency rates of 80% have been reported.418 Results reported in the upper arm are not as good. The unmasking of stenoses in close to 100% of cases warrants stenosis-detection programs similar to those for grafts.419
After thrombosis is established, resolution depends on local expertise. Interventional thrombectomy and PTA of the underlying stenosis have gained wide acceptance. Nevertheless, there are no results from a larger series of surgical treatment of AVF thromboses available. This leads to the astonishing fact that there are no comparable data available in this important field of access care.
Thrombosed fistulae can be declotted by using purely mechanical methods (dilation and aspiration),419 a thrombolytic,420 or a combination of both.421 Success rates are greater than 90% for the techniques. If a central vein stenosis is found, interventionalists frequently resort to the use of stents. Long-term results after dilation in the largest series are better in forearm native fistulae compared with grafts. Initial success rates for declotting are better in grafts compared with forearm fistulae, but early rethrombosis is frequent in grafts; thus, primary patency rates can be better for native fistulae after the first month’s follow-up.419 Although AVF function may be reestablished successfully as long as a week after thrombosis occurs, most should be treated as soon as possible.422
A variety of devices are available for mechanical thromboaspiration. With all, there are the issues of residual clots and cost-effectiveness of the devices over the simple procedure of catheter-directed aspiration. A meta-analysis should be performed.
Surgical thrombectomy is performed by using a Fogarty thrombectomy catheter, supported by retrograde digital expression of the thrombotic material and followed by correction of the stenosis by using a couple of techniques according to the individually varying condition. However, there are only scattered reports with initial success rates of only 65%423 compared with 90% or better for endovascular techniques. In a small study of 29 patients, a primary patency rate of 50% at 4 months was reported.424 Surgery seems to be the preferred technique to treat thrombosis in forearm AVFs with juxta-anastomotic stenoses, mainly by placement of a new anastomosis.424 With more proximally/centrally located thromboses, preference should be given to interventional endoluminal techniques. Early recurrence of stenosis/thrombosis can be decreased by insertion of a stent. On occasion, when both the artery and vein are thrombosed, conversion from a side-to-side to end-to-side anastomosis can be attempted, with the goal of using the newly created fistula immediately. This procedure was successful in 57% of 72 patients, particularly those with thrombosis of the AVF to the first side branch only, with the remaining fistula maintaining patency through collateral flow.425
Access Evaluation for Ischemia (CPG 5.6.1)
This evaluation should be a part of regular monitoring conducted routinely in all dialysis facilities. Particularly elder and hypertensive patients with a history of peripheral arterial occlusive disease and/or vascular surgery, as well as patients with diabetes, are prone to develop access-induced steal phenomenon and steal syndrome. In any case, clinical examination is mandatory, followed by ultrasound or radiological evaluation, as necessary. The patient must be referred to a vascular surgeon to decide on additional procedures. Delay can lead to catastrophic gangrene and hand amputation. The importance of this type of monitoring will increase in the future because of demographic changes in the dialysis population.
An AVF normally produces an alteration in blood flow patterns, a “physiological” steal phenomenon,426 that is seen in forearm AVFs and in a greater incidence in elbow/upper-arm AVFs.427 Physiological steal occurs in 73% of AVFs and 91% of AVGs.428 With the aging of the HD population and the increase in arterial changes caused by diabetes and hypertensive remodeling, the incidence of symptomatic peripheral ischemia to the hand/arm (pain, necrosis of ≥1 fingertips) is increasing, but fortunately is still uncommon (∼1% to 4%).48 Milder symptoms of coldness and some pain during dialysis may occur in up to 10% of cases and fortunately improve over weeks to months.429 It also is more common with prosthetic bridge grafts; less than 2% versus 4%.48,430 A decrease in distal perfusion pressures is found regularly and is more pronounced in patients with advanced arteriomedial sclerosis. In this type of patient, occurrence of a steal syndrome seems less dependent on access flow volume than on degree of the peripheral arterial obstructive disease.
Recently, staging according to lower-limb ischemia was proposed48:
Stage I, pale/blue and/or cold hand without pain;
Stage II, pain during exercise and/or HD;
Stage III, pain at rest;
Stage IV, ulcers/necrosis/gangrene.
It is important to differentiate the findings of hand ischemia from those of carpal tunnel compression syndrome, tissue acidosis, and edema from venous hypertension. Noninvasive evaluation should be performed, including digital blood pressure measurement, DDU, and—if available—transcutaneous oxygen measurement.48
Corrective results may be good at an early point in the process, but in any of these patients, one should be aware that the process of arterial damage could be progressive. Particularly in older patients with diabetes with an elbow/upper-arm AVF, monomelic ischemic neuropathy can be observed; an acute neuropathy with global muscle pain, weakness, and a warm hand with palpable pulses starting within the first hours after creation of the AVF.431 Diagnosis of monomelic ischemic neuropathy is a clinical diagnosis, and immediate closure of the AVF is mandatory.
Emergent Referral to a Vascular Access Surgeon (CPG 5.6.2)
Although most ischemic manifestations occur early after surgery, in about a quarter of all patients, they can develop months to years after arterial constrictions. Fingertip necroses are an alarming symptom with an initially slow progression in most patients over weeks and a rapid final deterioration leading to necrosis and gangrene, indicating that one should aim for early intervention. If ischemic manifestations threaten the viability of the limb, the outflow of the fistula should be ligated.
Therapeutic options depend on the cause of steal syndrome. Arterial stenoses proximal to the anastomosis obstructing the arterial inflow may be dilated by angioplasty,411 but not in the case of advanced general arterial calcification. High-flow–induced steal syndrome requires a decrease in AVF flow volume. Banding procedures of the postanastomotic vein segment using different techniques as practiced in the past were not as successful as expected.432 It is more beneficial to decrease the diameter of the anastomosis or create a new AV anastomosis distally. The success of the procedure after surgery should be evaluated by using access flow measurements.
In cases in which a physiological steal phenomenon becomes clinically symptomatic, ligation of the peripheral limb of the radial artery may be successful. Clinically symptomatic steal syndromes with normal or low BFRs represent the majority of cases with access-related peripheral ischemia. Since the new technique of the distal revascularization—interval ligation (DRIL) operation was published in 1988,429 several groups have confirmed the good results.48,433 In patients with a venous anastomosis to the brachial artery, with the DRIL procedure, the anastomosis is bridged by a venous bypass, after which the artery is ligated closely peripherally to the anastomosis. BFR into the AVF does not change substantially. Most patients do significantly better, presumably because of an increase in peripheral arterial perfusion.
In patients with low BFRs and signs of peripheral ischemia, the proximal AV anastomosis technique provides satisfactory results.434 The idea is to ligate the preexisting anastomosis to the brachial artery in the region of the elbow or distal upper arm and place a new arterial anastomosis in the proximal upper arm, somewhere near the beginning of the subclavian artery. Blood volume is brought down to the vein through an interposed vein graft or small-diameter PTFE graft. Thus, a sufficient BFR into the vein is provided and peripheral perfusion pressure is reestablished; cannulation for HD can be continued immediately.
Infection (CPG 5.7)
Although infections of fistulae are rare, any episode of infection potentially is lethal in face of the impaired immunologic status of long-term dialysis patients.
Very rare access infections at the AV anastomosis require immediate surgery with resection of the infected tissue. Should an arterial segment be resected, an interposition graft using a vein can be attempted or a more proximal new AV anastomosis may be created with exclusive use of degradable suture material.
More often, infections in AVFs occur at cannulation sites. Cannulation at that site must cease, and the arm should be rested.
In all cases of AVF infection, antibiotic therapy is a must, initiated with broad-spectrum vancomycin plus an aminoglycoside. Based on results of culture and sensitivities, conversion to the appropriate antibiotic is indicated. Infections of primary AVFs should be treated for a total of 6 weeks, analogous to subacute bacterial endocarditis.435 A serious complication of any access-related bacteremia is represented by metastatic complications, as described.159
Considerably fewer data have been published regarding management of complications in fistulae compared with grafts. Some aspects are “accepted” as the standard of care because they are described in standard surgical textbooks and surgeons/interventionalists accept them.
Guideline 6. Treatment of arteriovenous graft complications
Appropriate management and treatment of AVG complications may improve the function and longevity of the vascular access.
Patients with extremity edema that persists beyond 2 weeks after graft placement should undergo an imaging study (including dilute iodinated contrast) to evaluate patency of the central veins. The preferred treatment for central vein stenosis is PTA. Stent placement should be considered in the following situations:
Acute elastic recoil of the vein (>50% stenosis) after angioplasty. (B)
The stenosis recurs within a 3-month period. (B)
Indicators of risk for graft rupture:
Any of the following changes in the integrity of the overlying skin should be evaluated urgently:
Poor eschar formation. (B)
Evidence of spontaneous bleeding. (B)
Rapid expansion in the size of a pseudoaneurysm. (B)
Severe degenerative changes in the graft material. (B)
Indications for revision/repair:
AVGs with severe degenerative changes or pseudoaneurysm formation should be repaired in the following situations:
The number of cannulation sites are limited by the presence of a large (or multiple) pseudoaneurysm(s). (B)
The pseudoaneurysm threatens the viability of the overlying skin. (B)
The pseudoaneurysm is symptomatic (pain, throbbing). (B)
There is evidence of infection. (B)
Cannulation of the access through a pseudoaneurysm must be avoided if at all possible and particularly so if the pseudoaneurysm is increasing in size. (B)
Treatment of stenosis without thrombosis:
Stenoses that are associated with AVGs should be treated with angioplasty or surgical revision if the lesion causes a greater than 50% decrease in the luminal diameter and is associated with the following clinical/physiological abnormalities:
Outcomes after treatment of stenosis without thrombosis:
After angioplasty or surgical revision of a stenosis, each institution should monitor the primary patency of the AVG. Reasonable goals are as follow:
The treated lesion should have less than 30% residual stenosis and the clinical/physiological parameters used to detect the stenosis should return to acceptable limits after the intervention. (B)
A primary patency of 50% at 6 months. (B)
The clinical/physiological parameters used to detect the stenosis should return to acceptable limits after the intervention. (B)
A primary patency of 50% at 1 year. (B)
If angioplasty of the same lesion is required more than 2 times within a 3-month period, the patient should be considered for surgical revision if the patient is a good surgical candidate.
If angioplasty fails, stents may be useful in the following situations:
Surgically inaccessible lesion. (B)
Contraindication to surgery. (B)
Angioplasty-induced vascular rupture. (B)
Treatment of thrombosis and associated stenosis:
Each institution should determine which procedure, percutaneous thrombectomy with angioplasty or surgical thrombectomy with AVG revision, is preferable based upon expediency and physician expertise at that center.
Treatment of AVG thrombosis should be performed urgently to minimize the need for a temporary HD catheter. (B)
Treatment of AVG thrombosis can be performed by using either percutaneous or surgical techniques. Local or regional anesthesia should be used for the majority of patients. (B)
The thrombectomy procedure can be performed in either an outpatient or inpatient environment. (B)
Ideally, the AVG and native veins should be evaluated by using intraprocedural imaging. (B)
Stenoses should be corrected by using angioplasty or surgical revision. (B)
Methods for monitoring or surveillance of AVG abnormalities that are used to screen for venous stenosis should return to normal after intervention. (B)
Outcomes after treatment of AVG thrombosis:
After percutaneous or surgical thrombectomy, each institution should monitor the outcome of treatment on the basis of AVG patency. Reasonable goals are as follows:
A clinical success rate of 85%; clinical success is defined as the ability to use the AVG for at least 1 HD treatment. (B)
After percutaneous thrombectomy, primary patency should be 40% at 3 months. (B)
After surgical thrombectomy, primary patency should be 50% at 6 months and 40% at 1 year. (B)
Treatment of AVG infection:
Superficial infection of an AVG should be treated as follows:
Initial antibiotic treatment should cover both gram-negative and gram-positive microorganisms. (B)
Subsequent antibiotic therapy should be based upon culture results.
Incision and drainage may be beneficial.
Extensive infection of an AVG should be treated with appropriate antibiotic therapy and resection of the infected graft material. (B)
In this update of the KDOQI Guidelines, the Work Group did not perform a comprehensive literature and data review of recent studies of AVG complications. The primary change from previous versions of the KDOQI Vascular Access Guidelines is consolidation of related material on AVGs into a single unified guideline. However, the fundamental tenets are unchanged from previous editions. Newer references, including reviews, are included when appropriate.
Extremity Edema and Stenosis (CPG 6.1)
The AVG, although decreasing in frequency of use, remains a major type of vascular access for HD in the United States.2 The natural history of an AVG is the progressive development of neointimal hyperplastic stenoses in the outflow track. Although these stenotic lesions most commonly occur at the venous anastomosis, they also can occur at the arterial anastomosis and within the native veins that provide outflow from the AVG. This resulting increase in venous pressure leads to edema proximally and, in extreme circumstances, evidence of venous collateral flow. The presence of a hemodynamically significant stenosis can decrease the ability of the access to deliver adequate flow and increase the risk for AVG thrombosis. Early detection and treatment of hemodynamically significant stenoses is considered a primary tenet of a vascular access management program.
Extremity edema persisting beyond 2 weeks (immediate postoperative period) after placement of an AVG may indicate inadequate venous drainage or central venous obstruction.30,436 In many cases, the stenosis results from the prior placement of a subclavian catheter; risk for stenosis is increased by previous catheter infection.170 PTA of the stenotic or obstructed venous segment can lead to resolution of the edema. However, acute elastic recoil may occur after angioplasty of large central veins.437 Studies have shown that the use of stents may improve long-term patency of the central vein in certain circumstances.438-442 Surgical treatment of central venous stenosis is associated with substantial morbidity and should be reserved for extraordinary circumstances.443
Graft Degeneration and Pseudoaneurysm Formation (CPG 6.2, CPG 6.3)
Repeated cannulation of an AVG may cause degeneration of the graft material that can progress to involve the subcutaneous tissues overlying the vascular access.444,445 These degenerative changes may eventually compromise the circulation to the skin. Degeneration of the AVG and necrosis of the overlying subcutaneous tissue may lead to a progression of clinical problems, including difficulty achieving hemostasis upon needle withdrawal, spontaneous bleeding from cannulation sites, severe hemorrhage, and—ultimately—acute graft rupture. The degeneration of AVGs combined with a venous outflow stenosis fosters formation of a pseudoaneurysm. Progressive enlargement of a pseudoaneurysm produces thinning of the overlying skin, thereby accelerating skin necrosis that increases the risk for acute graft rupture. A large pseudoaneurysm can limit the availability of needle cannulation sites. Dialysis needles must not be inserted into a pseudoaneurysm. A severely degenerated graft or enlarging pseudoaneurysm should be repaired to decrease the risk for acute rupture and restore additional surface area for cannulation.
A pseudoaneurysm is treated most effectively by resection and segment interposition.106,446 Pseudoaneurysms that are not resected may expand and rupture, resulting in significant blood loss. Pseudoaneurysms that exceed twice the diameter of the graft or those that are increasing in size should be surgically corrected because of their increased risk for rupture. At times, an endovascular covered stent option may exist.447 Pseudoaneurysm expansion that threatens the viability of the skin places the patient at risk for graft infection. In these cases, surgical correction is indicated.
Treatment of Stenoses (CPG 6.4-6.8)
Venous stenosis is the most common lesion in AVGs, although in many cases, more than 1 lesion is present within the graft or at the anastomoses. Although previous studies suggested that arterial inflow lesions were uncommon (<5% of all lesions),108,266 more recent experience suggests the arterial or arterial anastomotic lesion affecting blood flow into the AVG may be up to 20% to 25% of all lesions identified by angiography.
A hemodynamically significant outflow stenosis decreases intragraft blood flow and increases intragraft pressure.10 The lower blood flow, in turn, may reduce the efficiency of HD treatment327,355 and increase the risk for vascular access thrombosis.285,287,322,340,347,364,376,448,449 Conversely, inflow lesions and intragraft lesions may be associated with low pressure in the body of the graft and venous outflow. A hemodynamically significant stenosis is defined as a 50% or greater reduction in normal vessel diameter accompanied by a hemodynamic, functional, or clinical abnormality (see CPG 4).449,450 By means of angiography, about 90% of thrombosed grafts are associated with stenosis, predominantly in the outflow, at the venous anastomosis, and more centrally.109,110,451,452
PTA or surgical repair of a hemodynamically significant stenosis associated with a nonthrombosed AVG can maintain functionality and delay thrombosis of the vascular access.269,453,454 Many nonrandomized trials have shown that preemptive treatment of stenoses reduces the rate of thrombosis10,322,374,455 and perhaps prolongs the useful life span of the AVG.10,322,374 A number of observational, but not randomized, studies show that a greater fraction of grafts remain free of interventions or thrombosis if the AVG is patent at the time of intervention.111,112,269,354,456 The fraction of AVGs free of further intervention or thrombosis ranged from 71% to 85% among 4 studies if PTA was performed preemptively compared with only 33% to 63% if PTA was performed after thrombectomy of the graft.10,322,374,455
Although these results would suggest that elective correction of stenoses before thrombosis might increase the long-term survival of the AVG, recent studies suggested that prophylactic treatment of stenoses, although reducing thrombosis events, does not extend the useful life span of AVG rates.384,386 Thus, the major reason for surveillance is the prevention of thrombosis (see CPG 4).
No convincing evidence exists showing that repair of an asymptomatic anatomic stenosis (>50% diameter reduction) improves function or delays thrombosis of the vascular access. Therefore, prophylactic treatment of a stenosis that fulfills the anatomic criteria (>50% diameter reduction), but is not associated with a hemodynamic, functional, or clinical abnormality, is not warranted and should not be performed.10,322,354
Arterial stenosis associated with diminished access inflow and frequently suspected by the presence of excessively negative dialysis circuit prepump pressures (arterial tubing to pump) should be evaluated and corrected when found.
After PTA, anatomic success is defined as residual stenosis less than 30%.20,457 Published series have consistently reported a 6-month primary (unassisted) patency rate of 40% to 50% after PTA of stenoses associated with nonthrombosed AVGs.108,111,112,269,354,456 The expected primary patency rate after surgical repair of stenoses associated with nonthrombosed grafts is less well established.458 Previous Vascular Access Work Groups have determined that a 1-year primary patency rate of 50% after surgical revision should be the goal.
Individual patients may have a rapid recurrence of stenoses that requires repeated PTA.108,453 In these patients, repeated angioplasty may not be cost-effective, and surgical revision may be beneficial. Previous Vascular Access Work Groups have defined rapid recurrence of a stenosis as the need for more than 2 angioplasty procedures within a 3-month interval.
Previous studies reported that the use of endovascular stents as the primary treatment for venous stenosis provides long-term results that are similar to those obtained with angioplasty alone.382,459-461 Stents should be reserved for patients with contraindications to surgical revision and for treatment of angioplasty-induced venous rupture.462-464
Several studies have directly compared percutaneous thrombectomy with surgical thrombectomy with revision for treatment of AVG thrombosis.465-470 A review of comparative and noncomparative studies reveals conflicting results and does not yield a definitive preference.24,106,356,467-479 In the opinion of the Work Group, percutaneous thrombectomy or surgical thrombectomy with revision are both effective techniques for the treatment of AVG thrombosis and associated stenosis. The thrombectomy procedure should be performed expeditiously to avoid the need for a short-term catheter. Hospitalization and general anesthesia increase the cost and risk of the thrombectomy procedure and should be avoided when possible.
An underlying stenosis frequently (>85%) is the cause of AVG thrombosis.108,480,481 Intraprocedural imaging should be used to evaluate the outflow veins for improved detection of significant stenoses.382,470 Identification and treatment of all significant stenoses are essential to optimize long-term patency of the thrombectomy procedure. PTA of stenoses associated with AVG thrombosis correlates with poorer outcomes compared with nonthrombosed AVGs.269 After percutaneous thrombectomy, the majority of reported 3-month primary (unassisted) patency rates range from 30% to 40%.471,473,476,478,480,481 The Work Group believes that percutaneous thrombectomy should achieve a 3-month primary patency rate of 40%. After surgical thrombectomy, the achievable goals are a 6-month primary patency rate of 50% and a 1-year primary patency rate of 40%. Surgical procedures are held to a higher standard because the AVG usually is extended farther up the extremity when a surgical revision of a stenosis is performed, using up “venous capital.”
Infection (CPG 6.9)
While cardiac causes account for almost half the deaths in adult patients with CKD stage 5, the second leading cause of death is infection, much of it related to the type of vascular access in use.60 AVGs have a greater rate of infection than autologous fistulae, and, unfortunately, antibiotics alone frequently are inadequate and surgical procedures are needed.482 Management of an AVG infection is a balance between achieving resolution of the infection while preserving the vascular access.59,483 Superficial infections should be treated initially with broad-spectrum antibiotic therapy. Subsequent antibiotic therapy should be based upon the identification of the causative bacterial organism.201,484 A more extensive AVG infection can lead to bacteremia, sepsis, and death. Surgical exploration and removal of infected graft material, combined with antibiotic therapy, often is necessary for complete resolution.484
Subclinical infection can develop in AVGs, typically resulting from retained graft material. Diagnosis may require performance of indium-labeled white blood cell or gallium scans. Such infection frequently is manifested as resistance to epoetin therapy, along with evidence of a systemic inflammatory response; frequently, it occurs in abandoned and nonfunctioning grafts. Epoetin responsiveness is restored only after removal of the graft.
Limitations and Comparison to Other Guidelines
These updated CPGs are essentially unchanged in content from those of previous editions of the KDOQI Vascular Access Guidelines. More evidence now is available for the guidelines than in previous editions. However, there is still a paucity of RCTs to better define the effect of interventions on clinically important outcomes. These guidelines also are comparable to those recommended by the Society of Interventional Radiology,457 American College of Radiology,485 and a joint committee of several surgical societies.458