Volume 49, Issue 2 , Pages 183-185, February 2007
In the Literature: Cognitive Impairment in Hemodialysis Patients
Article Outline
- What Did This Important Study Show?
- How Does This Study Compare With Prior Studies?
- What Should Clinicians and Researchers Do?
- References
- Copyright
All stages of chronic kidney disease are increasing in incidence and prevalence in the United States, with projections of a 35% to 100% increase in the prevalent US dialysis population during the next decade.1 Given the high prevalence of risk factors for cognitive impairment among patients with kidney failure treated by hemodialysis, including cardiovascular risk factors, hypertension, and hyperhomocysteinemia, these patients may be at increased risk of cognitive impairment.2, 3, 4
Cognitive impairment in dialysis patients could impact on both quality of life and the ability to make crucial social, economic, and health-related decisions that affect physical and emotional well-being, including obtaining a kidney transplant. Because of the complexity of medical and dietary regimens among dialysis patients, clinicians must recognize individuals who will experience difficulty with treatment plans and choices. Unfortunately, there are few studies of the incidence and prevalence of cognitive impairment, as well as risk factors for the development and progression of cognitive impairment, in the dialysis population. In their report in the July 2006 issue of Neurology, Murray et al5 showed a strikingly high prevalence of cognitive impairment in hemodialysis patients.
What Did This Important Study Show?
The investigators conducted a cross-sectional study of 338 prevalent hemodialysis patients aged 55 years and older from 16 dialysis units in Minnesota.5 Study participants did not differ significantly in age, sex, race, or education from 251 eligible patients who chose not to participate. The investigators matched a subset of 101 dialysis patients by age with 101 nondialysis patients who served as controls. The investigators assessed multiple domains of cognitive function in dialysis patients and controls to determine a global level of cognitive function by using a 45-minute neuropsychological battery. Tests were administered either before or at the initiation of dialysis or on a nondialysis day.
Among these 338 hemodialysis patients, 73% had either moderate or severe cognitive impairment, 14% had mild impairment, and only 13% had no impairment (Fig 1). Lower level of education and prior stroke were independently and strongly associated with severe cognitive impairment. A high dialysis dose (equilibrated Kt/V > 1.2, equivalent to a single-pool Kt/V of ∼1.6 in some studies) had a borderline association with severe cognitive impairment. After adjustment for age, sex, race, education, depression, diabetes, hypertension, and stroke, hemodialysis patients had a significantly increased risk of severe cognitive impairment (odds ratio, 3.54; 95% confidence limits, 1.28, 9.78) compared with nondialysis controls. Only 2.9% of dialysis patients in the study had a documented history of cognitive impairment before participation in their study, suggesting that clinicians may not recognize cognitive impairment and dementia in hemodialysis patients. Because the prevalence observed among dialysis patients was far greater than previously observed in patients with earlier stages of chronic kidney disease,2, 6 the investigators hypothesized that that the dialysis process itself may directly contribute to cognitive impairment, possibly by inducing cerebral ischemia or cerebral edema through intravascular volume loss and fluid shifts. Alternatively, the high prevalence of cognitive impairment may reflect the very high burden of comorbid conditions, including diabetes and cardiovascular disease.7
Figure 1.
Frequency of cognitive impairment in hemodialysis patients (adapted from Murray et al).5 Individuals with severe cognitive impairment scored 2 SDs or more below the age-adjusted population mean in 2 or more of the following cognitive domains (executive function, memory, and language). Those with moderate cognitive impairment scored 1.5 to 2 SDs below the age-adjusted mean in 2 or more domains or 2 or more SDs below the age-adjusted mean in 1 domain.
How Does This Study Compare With Prior Studies?
This relatively large cross-sectional study used a validated battery of cognitive tests to show that both moderate and severe cognitive impairment are common in the hemodialysis population. There are few studies of the prevalence and nature of cognitive impairment in patients with both earlier stages of chronic kidney disease and kidney failure treated by dialysis; those performed in dialysis patients generally predate more modern dialysis techniques, including the widespread use of high-flux and biocompatible dialysis membranes.4, 8 The study by Murray et al5 adds to these earlier findings by exploring cognitive impairment in a prevalent dialysis population across multiple cognitive domains.
The study had multiple limitations, including potential lack of generalizability because the study population was predominantly white (82.6%) and well educated (88.8% with high school or better) and had a lower prevalence of stroke and transient ischemic attack than observed in the wider US dialysis population (21% versus 29%). The participation rate in the study was moderate, with just more than 60% of eligible hemodialysis patients consenting to cognitive testing; however, there were no significant demographic differences between participants and nonparticipants. The association between high dialysis dose and severe cognitive impairment is unexpected and not well explained. Possibly, there is residual confounding caused by a lower volume of body water, as occurs in debilitating illness with loss of muscle mass, or residual confounding caused by fewer limitations to dialysis session time because of other functional impairments. Finally, the study did not examine other common conditions that might affect cognitive function in the elderly, including insomnia and sleep apnea.
What Should Clinicians and Researchers Do?
This study stresses that cognitive impairment is an important, highly prevalent, and underrecognized problem in the hemodialysis population. All practitioners caring for dialysis patients, including physicians, dialysis nurses and technicians, nutritionists, social workers, and others, need to be aware of cognitive impairment, particularly when instructing patients and involving family members in patient care. In addition, knowledge of a high prevalence of cognitive impairment suggests a need for more frequent advanced care planning.9
Future directions include validating these results in a more generalizable study population. Magnetic resonance imaging and functional brain imaging modalities could be helpful to delineate the causes of dementia and differentiate between vascular dementia, Alzheimer disease, and combinations of these entities. Longitudinal studies are necessary to determine risk factors for the development and progression of cognitive impairment in both dialysis patients and individuals with chronic kidney disease who have not yet reached the stage of kidney failure. These studies may show causal and potentially modifiable factors. Additional studies should compare cognitive function and progression of cognitive decline by using different dialysis modalities, in particular, those that minimize rapidity of volume and solute shifts, to understand the role of the dialysis procedure.
References
- Projecting the number of patients with end-stage renal disease in the United States to the year 2015. J Am Soc Nephrol. 2005;16:3736–3741
- . Cognitive impairment in chronic kidney disease. J Am Geriatr Soc. 2004;52:1863–1869
- . Cognitive function in dialysis patients. Am J Kidney Dis. 2005;45:448–462
- . Prevalence, recognition, and implications of mental impairment among hemodialysis patients. Am J Kidney Dis. 1997;30:41–49
- Cognitive impairment in hemodialysis patients is common. Neurology. 2006;67:216–223
- Moderate renal impairment and risk of dementia among older adults: The Cardiovascular Health Cognition Study. J Am Soc Nephrol. 2004;15:1904–1911
- . Cardiovascular disease and chronic renal disease: A new paradigm. Am J Kidney Dis. 2000;35(suppl 1):S117–S131
- . Neurocognitive function in chronic hemodialysis patients. Kidney Int. 1996;49:1435–1440
- . The creation of an advance care planning process for patients with ESRD. Am J Kidney Dis. 2007;49:27–36
Originally published online as doi:10.1053/j.ajkd.2006.11.035 on January 3, 2007.
PII: S0272-6386(06)01709-4
doi:10.1053/j.ajkd.2006.11.035
© 2007 National Kidney Foundation, Inc. Published by Elsevier Inc All rights reserved.
Volume 49, Issue 2 , Pages 183-185, February 2007
