(1) Medizinische Klinik und Poliklinik IV, University Hospital Munich, Munich, Germany
(2) Medizinische Klinik, SRH Wald-Klinikum, Gera, Germany
* Corresponding author Email: firstname.lastname@example.org
Renewed interest in convective renal replacement therapy is fuelled by the desire to reduce high mortality of current maintenance dialysis patients. Although encouraging data have been obtained from retrospective analyses or prospective cohort studies, widespread implementation of online haemodiafiltration has been hampered by lack of conclusive evidence of improved survival compared to haemodialysis. This review discusses standard care for end-stage renal disease patients.
Recently, three large randomised trials have been published which compared online haemodiafiltration to high- or low-flux haemodialysis. Primary analysis from ESHOL trial and secondary analyses from the Convective Transport Study and the Turkish Online Haemodiafiltration study found that high convective volumes confer a survival benefit to haemodiafiltration patients. However, the evidence from these three studies is not unanimous and each of these trials has been criticised for selection bias or violation of the study protocol. Moreover, it is not clear why some patients who were randomised to high-volume online haemodiafiltration were able to achieve high convection volumes and others were not. Confounding factors for patient selection may have been differences in vascular access or cardiac function determining whether patients could achieve high convection volumes rather than the prescribed protocol.Thus, it is plausible that better survival rates in those with better vascular access simply reflect ‘healthier’ patients.
A consistent theme that emerges from all three trials is that actual replacement volume seems to matter. Higher volumes were associated with better survival. Mechanisms underlying reduction of all-cause mortality remain obscure, but may involve better removal of uraemic toxins, less systemic inflammation and a lower number of intradialytic hypotensive episodes.
In future, online haemodiafiltration will be frequently used. However, there is an urgent need to define the required minimum/optimal convection volumes (expressed as litres per body weight or per surface) in end-stage renal disease patients who are eligible for online haemodiafiltration by well-designed trials.