Effects of EPO therapy on backfiltration of dialysate in high flux dialysis

The authors have developed a comprehensive mathematical model of the hemodialysis process to investigate the effect of r-HuEPO and the accompanying higher hematocrit on backfiltration in high flux dialysis. Model simulations indicate that under otherwise identical conditions typical of high flux dialysis, an increase in hematocrit from 20 to 33% will increase the amount of dialysate fluid entering the blood from 2.4 L to 3.8 L in a 4 hr treatment. We used the mathematical model to investigate the effect of the following variables on backfiltration: blood flow rate, ultrafiltration rate, inside fiber diameter, fiber length, and membrane permeability. While increasing the blood flow rate may enhance solute transport, it was found to increase backfiltration substantially through its effect on the axial pressure drop. This effect was most pronounced at the higher hematocrits due to the higher viscosity. It was found that increasing the fiber ID, decreasing the fiber length, and decreasing the permeability of the membrane (all at constant surface area) could be beneficial in reducing backfiltration. However, these results do not consider the potential negative impact of these changes on solute clearance. Finally, the mathematical model enhanced our understanding of the transport processes governing backfiltration. Due to protein concentration gradients in the lumen, protein osmotic pressures as high as 50-100 mmHg can be obtained in high-flux dialysis. As a result, providing an outlet hydrostatic blood pressure greater than the inlet hydrostatic dialysate pressure is not sufficient to guarantee the absence of backfiltration.