Measurement of access flow during hemodialysis using the constant infusion approach

With reversed placement of blood lines and with a peripheral arteriovenous access, hemodialysis recirculation (R) consists of a local access component, and a central cardiopulmonary component that must be separated for the calculation of access flow (Q(ac)) using indicator dilution principles. With indicator injections that follow constant infusion principles Q(ac) = (1 - R-x)/(R-x(1 - CPR)) x (Q(b,x) - UFR), where Q(b) is the extracorporeal blood flow, where UFR is the ultrafiltration rate, and where the index x indicates reversed placement of blood lines. CPR, the amount of cardiopulmonary recirculation (CPR = Q(ac)/CO) is determined from two recirculation measurements with correct (index n) and with reversed (index x) placement of blood lines CPR = R-n(1 - R-x)/R-x(1 - R-n) x (Q(b,x) - UFR)/Q(b,n). Q(ac) was measured in 11 hemodialysis (HD) patients using a thermodilution device tested in an in vitro set-up based on constant infusion principles. Mean Q(ac) was 1.135 L/min and 1.054 L/min for measurements done early and late in dialysis. The coefficient of variation was +/-7.3% and +/-8.6%, respectively. Repeated measurements of access flow in HD patients showed good reproducibility (Q(ac.1) = 1.01*Q(ac.0), r(2) = 0.98), with the regression line not different from the line of identity; however, in vivo results remain to be validated by an independent technique.