A Quest for a Pot of Gold

In the quest for bettersolute clearance, two divergent paths were taken on each side of the Atlantic.The US nephrology community has concentrated more on low weight molecules. The Europeancounterpart has focused on both low and middle weight molecules.The European endeavor hasled to the evolution of the on-line hemodiafiltration (HDF), combining HF andHD. A water-permeable filter allows middle molecule removal by convection.Dialysate then supplements low molecular weight solute removal by diffusion. Production ofthe replacement fluid from dialysate in the circuit (thus called “on-line”) cuts thecost.Since Fresenius’ Online Plus™came out in 1998, on-line HDF has gained popularity in Europe and othercontinents. In the US? Not so much, but we may see it more as it was justcleared by FDA for the market this April.The idea of middle moleculeremoval sounds physiological. But is there really any advantage?It has been suggested thatthe on-line HDF may reduce intra-dialytic hypotension, improve nutritionalstatus, and decrease ESA (erythropoiesis stimulating agent) requirement. Butwhat about the hard end points (all-cause mortality and cardiovascular outcomes)?In the recent CONTRAST study, 700 patients in the Netherlands, Canada, and Norway wererandomized to on-line HDF or low-flux HD. The surprise? There was no CONTRASTbetween the two groups… The CONSOLATION was a minimal survival benefit amongthose who received top-quartile convective volume. Didthis disappoint the nephrology community? Yes, to some extent. In arecent CJASN editorial, Dr. Kuhlman from Germany pointed out  that in Europe the advantages of on-line HDFover conventional HD have been “somehow taken for granted”.Didthis put an end to on-line HDF? The answer is no. A couple of more Europeanstudies are on their way, so is the research to solve technical challenges. Thisis a never ending journey, even if it may end up with the quest for a pot ofgold at the end of the rainbow.
Posted by Tomoki Tsukahara