Is it time to wake up to online Hemodiafiltration?
Posted May 05 2013 12:00am
There has been a lot of interest recently in online
Hemodiafiltration (olHDF) with multiple studies
published in the past year. It is a technique which has gained favor in
Europe (albeit with a lack of hard evidence) while being not utilized at all in
the US for various reasons. HDF involves the addition of convective clearance,
hemofiltration, to the diffusive treatment of hemodialysis (HD) which gives
better clearance of middle sized uremic toxins. Very large volumes of plasma
water are ultrafiltered using a high flux dialyzer with replacement solution
needed to maintain fluid balance. As a large volume of fluid is infused
directly into the patient, this infusate needs to be ultrapure with low levels
of pyrogen and microbial contamination. The development of online generation of
ultrapure replacement fluid, directly from the water treatment plant, has
facilitated the roll out of olHDF in Europe. Safety concerns have also been
addressed. Previously reported benefits, apart from middle molecule clearance,
have included better phosphorous removal, improved intra-dialytic blood
pressures, lower levels of EPO resistance, improved quality of life among
others but hard outcome data has been lacking until recently. The past year has
seen the publication of 3 randomized controlled trials examining olHDF versus
The Convective Transport Study randomly assigned 714
patients to either olHDF or low flux HD. There was no difference between the
groups in the primary outcome of all-cause mortality after a 3 year follow-up.
However, in post-hoc analyses, receiving high dose olHDF (>22L of convective
volume per session) was associated with a lower all-cause mortality compared to
low flux HD (HR 0.62).
Turkish olHDF Study
This study randomized 782 patients to olHDF or high flux HD.
The composite endpoint of all-cause mortality and nonfatal cardiovascular event
rate was not different between the groups after a 2 year follow-up. However,
again in a post-hoc analysis, a higher delivered dose of convective clearance (>17.4L,
the median clearance) was associated with a lower risk of overall (RR 0.54) and
cardiovascular mortality (RR 0.29).
Spanish olHDF Study
The latest study set out to deliver a high dose of
replacement fluid and they succeeded (median convective volumes approximately
23L). They assigned 906 patients to either continue their current modality (mostly
high flux HD) or switch to olHDF. The primary outcome of all-cause mortality
occurred 30% less frequently in the olHDF group (p=0.01) after approximately 2
Verdict: My previous experience with olHDF involved using it
in an ad-hoc basis for patients with uremic symptoms despite ‘adequate’ KT/V
urea or in patients with long dialysis vintage (extrapolating results from the
HEMO study as high flux HD is a form of low dose HDF). Many European
Nephrologists have presumed outcomes would be better but with very little data
to back that up. We now have 3 RCTs suggesting a relationship between high dose
olHDF and improved mortality. In our dialysis patients with such high mortality
and with few interventions proven to impact this over decades, these results
should be appreciated by the Nephrology community. It is at least time to
reconsider the barriers to its use.