Hemodiafiltration: Technical and Clinical Issues.

Hemodiafiltration (HDF) seems to represent the gold standard in the field of replacement of renal function by dialysis. High convective fluxes have been correlated with better clinical outcomes. Sometimes, however, there are technical barriers to the achievement of high blood flows adequate to perform effective convective therapies. In spite of optimized procedures, the progressive increase in transmembrane pressure (TMP), the blood viscosity due to hemoconcentration and blood path resistance sometimes becomes inevitable. We propose two possible solutions that can be operated automatically via specific software in the dialysis machine: predilution on demand and backflush on demand. Predilution on demand consists in an automatic feedback of the machine, diverting part of the filtered dialysate into a predilution mode with an infusion of 200 ml in 30 s while the ultrafiltration pump stops. This produces a sudden hemodilution with a return of the parameters to acceptable values. The performance of the filter improves, and the pressure alterations are mitigated. Backflush on demand consists in an automatic feedback of the machine triggered by the TMP control, producing a positive pressure in the dialysate compartment due to a stop of filtration and rapid infusion of at least 100 ml of ultrapure dialysate into the hollow fiber. This not only produces a significant hemodilution, but also backflushes the membrane pores detaching protein layers and improving membrane permeability. These are two examples of how technology will permit to overcome technical barriers to a widespread diffusion of HDF and adequate convective dose delivery.