BACKGROUND The influence of differing blood tubing sets on delivered dialyzer blood flow (Q B ) was studied using ReadySet (RS; Medisystem Inc, Seattle, WA) and CombiSet (CS; Fresenius, Walnut Creek, CA).
Methods: In vitro, we measured Q B and pre-pump arterial pressures (P A; in millimeters of mercury) during 4 hours at a prescribed blood pump flow (Q P ) of 450 mL/min, using a glycerin-water mixture for RS and CS blood tubing sets (n = 10 each). We then performed 3 clinical studies to determine the difference between Q P and Q B as a function of P A for both tubing types and any effects of tubing type on delivered Kt/V in patients.
Results: In vitro, 4-hour time-averaged Q B was 451 mL/min with RS versus 422 mL/min with CS. Q B was approximately 40 mL/min greater using RS than CS blood tubing sets at Q P of approximately 445 mL/min with [Q P - Q B ] increasing linearly with P A for CS, but not RS (study 1). At a mean Q P of approximately 408 mL/min, CS blood tubing significantly increased Kt/V by approximately 0.1 (90 patients; study 2). In study 3, [Q P - Q B ] increased with treatment time with CS (8 to 29 mL/min), but not RS (from -4 to 6 mL/min). For patients achieving equal Q P of 400 mL/min or greater for all treatments (n = 11), paired analysis showed greater values for urea reduction ratio (+3.5%; P = 0.039) and Kt/V (+0.14; P = 0.04) with RS than CS tubing sets.
Conclusion: Differences in [Q P - Q B ] occur both in vitro and in vivo, are much smaller with RS than CS tubing sets, and result in a greater delivered Kt/V of up to 0.14 for RS.