Internal filtration induces severe concentration of blood cells inside hollow-fiber dialysis membrane at the start of postdilution hemodiafiltration

Abstract

The hydraulic permeability of the dialysis membrane used for hemodiafiltration (HDF) is high, so that a large amount of internal filtration occurred in addition to ultrafiltration required for water removal and fluid replacement. Especially for the period immediately after the start of HDF, severe concentration of blood cells by internal filtration is likely to occur. The aims of this study was, using a mathematical simulation, to evaluate the amount of internal filtration and resulting blood cell concentration inside the hollow fiber and to develop a strategy to avoid the severe hemoconcentration during postdilution HDF. To this end, we calculated maximum internal filtration rate, and maximum hematocrit at varying blood flow rate, dialysate flow rate, and ultrafiltration rate. We found that at the start of the HDF, severe concentration of blood cells can occur where maximum hematocrit reached over 60%, even the dialyzer was designed to ensure minimal internal filtration. The hemoconcentration was not actually severe after membrane fouling occurred. To prevent the initial severe concentration of blood cells during HDF, at the start of the treatment the blood and dialysate flow rate should be below 100 ml/min and no ultrafiltration should be performed.