The Convertibility of Online Clearance Measurements

Extracorporeal blood flow. Left panel: Measured (crosses) and assumed (closed circles) stroke volumes V_s versus arterial line pressure P_art described by linear regression functions (full and broken lines). Notice that for a given preload measured, V_s was always larger than that assumed by the machine. Right panel: Ratio of measured to displayed blood flow expressed as relative blood flow (Q_rel) with (crosses) or without (closed circles) correction for variable preload versus P_art described by linear regression functions (full and broken lines). Notice that with correction for preload (crosses), the measured blood flow was always higher than that given by the dialysis machine (100% line), whereas without correction (closed circles), measured blood flow only fell below that displayed by the dialysis machine (100% line) when P_art was less than −150 mm Hg. Measurements were done at 37°C with flows ranging from 100 to 500 mL/min using a 4008 B dialysis machine and arterial line sets with an 8-mm pump segment (Fresenius Medical Care, Schweinfurt, Germany).