Abstract
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.
Highlights
Hemodiafiltration (HDF) adds convective elimination of middle molecules (MM) on the top of diffusionbased elimination of small molecules (SM) by conventional hemodialysis (HD)
Unlike the situation in SM range, where the “relative dialysis dose” Kt/V is generally accepted as its adequacy marker with its target value defined by randomized controlled studies [1, 2] and included in existing guidelines [3, 4] there is only a general consensus that the “absolute dialysis dose” in MM range may be represented by the convective volume (Vconv)
The so far most elaborated approach has been offered by Daugirdas [21] using the ratio of total body water V and body surface area BSA to define a modified Kt/V: modKt/V =
Summary
Hemodiafiltration (HDF) adds convective elimination of middle molecules (MM) on the top of diffusionbased elimination of small molecules (SM) by conventional hemodialysis (HD). No consensus exists as to which anthropometric parameter should be used to convert that absolute dose into a relative one which would enable to compare HDF efficacy in different individuals. From among the plethora of studies on online HDF, only one study [5] provided some data for the search of a suitable anthropometric parameter applicable for Vconv normalization needed to find its upper target value above which no further benefit for the patient could be expected. Vconv normalized by BSA indicates that mortality of patients on HDF may be reaching its bottom plateau for values of Vconv/BSA around 15 L/m2
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