Principles and practice of internal Hemodiafiltration

It has recently been suggested that the potentials of modern high-flux membranes could be exploited with the so-called internal hemodiafiltration (iHDF) technique. In principle, iHDF works just as high-flux hemodialysis but requires the convective dose to be clinically relevant, quantifiable and possibly adjustable by the operator. In this chapter, we briefly survey the theoretical, technological and practical aspects of iHDF, focusing on the mechanism ensuring its convective potential, i.e. the internal filtration/backfiltration (IF/BF) phenomenon. Based on theory, it is highlighted that the enhancement of the convective dose during iHDF relies upon a wise design of the hemodialyzer, both in terms of membrane performance and of hydrodynamics, whereas the adjustment of convection is feasible by proper regulation of the treatment parameters. IF/BF measurements appear to be feasible by indirect means; however, investments are needed to bring technology from the mere research field to the clinical practice. An alternative approach to IF/BF quantification is using mathematical models provided that the developed calculation tools are handy enough for the clinician, or even be implemented in the dialysis machine itself. IF/BF 'calculators' also represent a means to make the clinical staff conscious of the filtration phenomena that take place inside a high-flux hemodialyzer. It is concluded that iHDF is a possible complementary, simplified technique which could increase the clinical diffusion of high-flux convective treatments in the near future. Copyright (c) 2007 S. Karger AG, Basel.