A theoretical model to predict the in vitro performance of hemodiafilters

In vitro tests with saline or plasma replacing the blood are generally used in the development of membranes and membrane modules for hemodiafiltration (HDF) and for quality control purposes. Theoretical models predicting perf ormance of a hemodiafilter based on module geometry, membrane properties an d operating conditions are needed, but are not yet available, to distinguis h to what extent membrane properties and module fluid dynamics both affect module clearance. In this paper, we report on the development of a simple predictive model fo r hemodiafiltration which still accounts for those phenomena that most prof oundly affect performance of hemodiafilters, such as: the dependence of mas s transport coefficients on the actual flow conditions; concentration polar ization; the actual water filtration flux along the hemodiafilter length. T he model was validated with respect to data in literature. Model prediction s for low to high molecular weight solute clearance were within 10% of expe rimental data when saline replaces the blood and within 20% when plasma rep laces the blood, at blood flow rates ranging from 100 to 500 ml/min and net overall filtration flow rates from 0 to 60 ml/min. Under all conditions, t he model predicted clearances were in better agreement with experimental da ta than those predicted by other, non-predictive models for HDF. (C) 2000 E lsevier Science B.V. All rights reserved.