Why choose high volume online post-dilution hemodiafiltration?

The mortality rate of patients on maintenance dialysis remains alarmingly high, at approximately 15-20 % per year. Increasing dialyzer urea clearance has not been shown to improve survival and hence interest has shifted towards convective therapies, such as hemodiafiltration (HDF) which can remove middle molecular weight uremic toxins, which have been suggested to increase mortality in patients with end-stage kidney disease. During the last few years, four large prospective randomized controlled trials (RCTs) have been conducted in different European countries to compare survival outcomes in prevalent patients receiving conventional hemodialysis with online post-dilution HDF (OL HDF). Furthermore, a pooled individual participant data analysis from four RCTs was performed and four large meta-analyses on convective therapies have been published in the last 2 years. Taken together, these studies support the conclusion that high volume post-dilution OL HDF is associated with improved overall survival. This advantage results predominantly from a lower cardiovascular mortality, possibly due to better preservation of left ventricle mass and function. Improved intra-dialytic blood pressure stability may contribute to the beneficial effect of high volume post-dilution OL HDF on survival. The beneficial effect is not restricted to selected subgroups, such as age, comorbidity or dialysis vintage. There is no compelling evidence that high volume post-dilution OL HDF reduces mortality by improvements in traditional and non-traditional risk factors. There are still no studies or case reports published describing adverse clinical outcomes in more than 20 years of HDF clinical experience. In conclusion, most of the available data support the choice of high volume post-dilution HDF over the current dialysis techniques. However, considering that we live in the era of evidence-based medicine, the evidence supporting the superiority of high volume post-dilution OL HDF in comparison to hemodialysis is still missing: in fact, a new RCT targeting different convection volumes would be needed to definitively examine the dose-response effect shown in previous studies.