Hemodiafiltration is a trend of blood purification therapy for end-stage kidney disease patients in most European countries and in Japan. In intermittent infusion HDF (I-HDF), a part of dialysate is infused intermittently to the blood during treatment. Recover of the solute permeability may be expected with the infusion of dialysate by back filtration across the membrane. In our previous study, more effective recovery of solute removal performance was achieved by generating back filtration intensively around the areas where fouling was severely formed. Therefore, in this study, the infusion methods with a higher flushing effect were investigated by performing I-HDF experiments in aqueous in vitro system.

Inulin (MW 5,000) and bovine serum albumin (MW 66,000) were dissolved in ion-exchanged water to prepare a test solution. The test solution and dialysate were pumped into a diafilter at a flow rate of 250 and 500 mL/min, respectively. The ultrafiltration rate (forward filtration) was set to 0, 15 or 30 mL/min. At every 30 minutes, the dialysate flow was stopped, and phosphate-buffered solution was infused at both inlet and outlet of the dialysate line using two extra pumps. The back filtration was induced for 40 seconds at the flow rate of 300 mL/min. The solute removal performance was evaluated by the clearance for inulin and the amount of albumin leakage.

Clearances for inulin declined over time, and no difference was observed between with and without back filtration regardless of ultrafiltration rates. Although the amount of albumin leakage increased by performing back filtration at the ultrafiltration rate of 0 and 15 mL/min, the effect of back filtration became smaller at the ultrafiltration rate of 15 mL/min, and there was little effect at 30 mL/min. Considering these results, albumin adsorbed onto the membrane, and micropores were clogged with albumin, resulting the decrease of solute remove performance. The fouling formed under relatively low ultrafiltration rate was partially removed by back filtration. However, when the membrane was fouled severely due to a large amount of ultrafiltration, back filtration was not very effective to remove the fouling and to recover the solute removal performance. In conclusion, it was found that...