Background: Although different on-line convective removal strategies are available, there are no studies comparing the efficiency of solute removal for the three main options [post-dilution haemodiafiltration (post-HDF), pre-dilution haemodiafiltration (pre-HDF) and pre-dilution haemofiltration (pre-HF)] in parallel.
Methods: In this study, we compared post-HDF (Polyflux 170), pre-HDF (Polyflux 170) and pre-HF (Polyflux 210) in 14 patients. Parallelism of the evaluation protocols consisted in applying the same blood flow, dialysis time and effective convection (22.9 +/- 1.7 versus 22.2 +/- 2.0 L, P = NS) in pre-HDF versus post-HDF, and the same blood flow and dialysis time while comparing pre-HDF and pre-HF (1:1 dilution). With pre-HF, ultrafiltration was maximized and resulted in an effective convective volume of 28.5 L. We studied water-soluble compounds (urea, creatinine, uric acid), protein-bound compounds (hippuric acid, indole acetic acid, indoxylsulfate and p-cresylsulfate) and beta(2)-microglobulin (beta(2)M).
Results: Post-HDF was superior to pre-HDF for water-soluble compounds and beta(2)M, whereas there was no difference for protein-bound compounds. Pre-HDF was superior to pre-HF for water-soluble compounds and protein-bound compounds. In contrast, removal of beta(2)M for pre-HF was higher than for pre-HDF, but it did not differ from that obtained with post-HDF.
Conclusions: It is concluded that post-dilution is superior to pre-dilution HDF under conditions of similar convective volume, and that HDF is superior to HF in pre-dilution, with the exception of removal of beta(2)M. Overall, post-HDF is the most efficient convective strategy among those tested.