Constant blood flow during single-needle dialysis is unnecessary.

Single-needle (SN) dialysis employs tidal blood flow at the point of vascular access. The simplest SN systems convert this tidal flow to a pulsatile flow in the dialyser. It has been assumed that constant flow through the dialyser is necessary for optimal efficiency. Therefore SN blood circuits are designed to smooth the pulsatile flow in the dialyser to a relatively constant flow. This increase the complexity and cost of the SN system. In order to test the hypothesis that pulsatile flow results in lower clearances than constant flow, we performed measurements of clearance in vitro using pulsatile blood flow at time-averaged rates of 50-250 ml/min and tidal volumes 200-100 ml/min. These were compared with clearances using constant blood flow at the same rates. At all flow rates and at tidal volumes up to 50 ml, the clearance measurements obtained during pulsatile flow were identical to those obtained during constant flow.