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