Place of on-line hemodiafiltration in renal replacement therapy for chronic end-stage renal disease in 2021: Current status and perspectives

Hemodiafiltration (HDF) is a renal replacement therapy that combines diffusion and convection in the same dialyzer and offers currently the most efficient dialysis modality per time unit. Online HDF (ol-HDF) reflects the fact that ultrafiltered fluid is continuously compensated by an isovolumic substitution fluid produced from fresh dialysate by a cold sterilization ultrafiltering process. By combining diffusive and convective clearances, ol-HDF maintains a high diffusive clearance for solutes of low molecular weight equivalent to that of high permeability hemodialysis and increases the elimination of solutes of higher molecular weight comparable to that obtained in hemofiltration. The safety and sustainability of ol-HDF is based on numerous clinical studies and on the growing acceptance of this treatment modality worldwide. Thus, nearly 400,000 patients were receiving treatment with ol-HDF at the end of 2020. The safety and efficacy of ol-HDF are based on strict rules which include the regular use of ultrapure water, the use of machines certified for ol-HDF, the compliance with strict hygiene measures and with good clinical practices. Short-term prospective studies have shown that ol-HDF increases the elimination of uremic toxins of medium and high molecular weight, improves hemodynamic tolerance and offers various clinical benefits. The main driving force behind ol-HDF's efficacy and clinical benefits is the total ultrafiltered volume per session (i.e., the convective dialytic dose). This is the reason why special attention must be paid by caregivers to achieve this optimal convective dose by adapting clinical practices to this goal. Short-term prospective studies have provided intermediary outcomes showing that hemodiafiltration enhanced solute removal of middle and large molecular size solutes, improved hemodynamic tolerance and further various clinical benefits. The main driving force supporting the ol-HDF efficacy and clinical benefits depend on the total ultrafiltered volume delivered per session (namely dialytic convective dose). A particular clinical attention should be given by care givers to achieve such optimal convective dose in adapting practice patterns to this aim. In addition, the prescription of HDF may differ around the world, but the convective dose is still just as important. For example, in the western world postdilution ol-HDF is largely predominant while in the eastern world predilution HDF is the most widely used today for a variety of reasons. Four prospective randomized trials were conducted in Europe with inconclusive results on the primary outcomes. All trials, however, identified a positive relationship between convective dose and clinical outcome. This finding was confirmed in an individual analysis of patient data carried out on the entire database of these 4 randomized clinical trials. Two large randomized studies (CONVINCE and H4RT) respecting a minimum convective dose are underway in Europe and will make it possible to fill these gaps in evidence-based medicine. This chapter summarizes the basic physical bases of ol-HDF, regulatory aspects, prescription, epidemiological development and current clinical results. (C) 2022 Societe francophone de nephrologie, dialyse et transplantation. Published by Elsevier Masson SAS. All rights reserved.