Dialyzers for hemodiafiltraion

Hemodiafiltration (HDF) is currently the most effective dialysis therapy, combining diffusion with convective transport, up to substances with a molecular weight (MW) of 50 kilo Dalton (kD). To achieve large convection volumes (>21-22 L/session), a high transmembrane pressure (TMP) is necessary. As the substitution fluid is infused after the dialyzer in postdilution HDF, which is the most frequently used HDF mode today, considerable hemoconcentration may occur within the dialyzer. Therefore, a pre-requisite to perform HDF safely and efficient is the selection of an adequate dialyzer. In this respect, both an optimal solute clearance with minimal albumin loss, excellent biocompatibility and endotoxin retaining capacity are fundamental aspects of the filter. Hence, it seems obvious that permeability should be high enough and the membrane surface area sufficiently large to achieve high convection volumes. In clinical practice, however, the magnitude of the convection volume appeared relatively independent of the dialyzers used, varying considerably in membrane surface area and length of capillaries. Hence, further research on this topic is urgently warranted.