Effect of Low Dialysate Flow Rate on Hemodialyzer Mass Transfer Area Coefficients for Urea and Creatinine.

Recent work has shown that the dialyzer mass transfer area coefficient (Ko A) for urea increases when the dialysate flow rate is increased from 500 to 800 mL/min. In this study we determined urea and creatinine clearances for two commercial dialyzers containing polysulfone hollow fibers in vitro at 37°C, a nominal blood flow rate of 300 mL/ min, and dialysate flow rates (Qd ) ranging from 100 to 800 mL/min. A standard bicarbonate dialysis solution was used in both the blood and dialysate flow pathways, and clearances were calculated from solute concentrations in the input and output flows on both the blood and dialysate sides. Urea and creatinine Ko A values, calculated from the mean of the blood and dialysate side clearances, increased (p < 0.01) with increasing Qd over the entire range studied. The increase in both urea and creatinine Ko A with increasing Qd was proportional to the Ko A value. These data show that changes in Qd alter small solute clearances greater than predicted assuming a constant Ko A.