The impact of erythropoietin on hemodialyzer design and performance

The present study investigated theoretically and experimentally the effects of increases in hematocrit on the clearance of urea by the Baxter ST15 hollow fiber dialyzer. In a theoretical model that incorporates the three component resistances for the overall mass transfer rate, namely, the resistance of the blood (Rb)-, membrane (Rm)-, and dialysate side (Rd), it was predicted that a change in hematocrit would alter only the blood side resistance. The overall impact of this alteration is expected to be determined by the relative contribution of Rb to the overall resistance (RO). The modest contribution of Rb to RO implies that a major change in Rb (50%) would have only a minor effect on RO (11%) and consequently on urea clearance (5%). These theoretical conclusions were tested experimentally and the results confirmed the theoretical predictions. Indeed, there was little change in urea clearance in the clinically relevant range of variations in hematocrit (19-39%). Possible ways of compensation by minor changes in the hollow fiber geometry are discussed as well as the more complex relationships with larger solutes (creatinine) or unequally distributed solutes (potassium, phosphate).