Hemodiafiltration (HDF) adds convective elimination of middle molecules (MM), proportional to filtered volume (Vconv) on the top of diffusion-based elimination of small molecules (SM) by conventional hemodialysis (HD). Studies, both observational and randomized controlled ones, performed so far generally indicated positive impact of higher Vconv on all-cause mortality in HDF patients, although the magnitude of Vconv at which HDF becomes apparently superior to HD differed widely among the studies. Also the issue of a suitable anthropometric parameter by which the Vconv should be normalized has not yet been solved. Data from the ESHOL study seems to indicate that patient´s body surface area (BSA) could well be used for this—mortality was decreasing with increasing Vconv/BSA with a bottom plateau starting at about 15 L/m2 . We have therefore devised a formula and a graph for determination of Vconv which fulfils the requirement Vconv/BSA = 15. Assuming maximum feasible and safe filtration fraction QF/QB = 0.3, the Vconv actually defines the necessary blood flow (QB) to reach Vconv/BSA = 15 as QB = 15·BSA/(0.3·t) (t – session time). It is also possible to check what QB is needed in terms of sufficient diffusion-based transport (target Kt/V) and compare both QB values to see if adequate combined elimination of both SM and MM can be achieved at the same time and under what conditions, respectively.

Department of Medicine General University Hospital Prague Prague Strahov Czech Republic

Department of Physics Faculty of Electrical Engineering Czech Technical University Prague

Institute of Biophysics and Medical Informatics 1st Faculty of Medicine Charles University Prague

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