Haemodiafiltration at Higher Volumes and Patient Survival

Patient morbidity and mortality rates are still very high in standard low-flux haemodialysis (lf-HD). On-line haemodiafiltration (OL-HDF) is considered the most efficient dialysis technique, as clearances of small solutes, like urea, may be even higher than in lf-HD and clearances of middle solutes, like β2-microglobulin, are much higher than in lf-HD. OL-HDF has been suggested to reduce mortality compared to HD, possibly due to more effective removal of larger uraemic retention solutes and/or better fluid removal. Only 1 out of the 3 largest randomized trials was able to demonstrate a positive effect of OL-HDF on patient survival in comparison to those randomized to HD. Post hoc analyses of these studies consistently showed that the patients randomized to OL-HDF who received the highest convection volumes had a lower risk of mortality and cardiovascular events than those randomized to HD. Four meta-analyses showed inconsistent results concerning the effect of convective treatments in improving general and cardiovascular survival, while they showed a significant reduction of the intradialytic symptomatic hypotension. An individual pooled participant analysis of the 4 largest trials confirmed these findings, suggesting a better survival when a convection volume of at least 23 litres/session was delivered, while other studies did not confirm these conclusions. Even after extensive statistical adjustments, residual confounding always remain; therefore, randomized control trials targeting different convection volumes are required to definitively confirm a dose-response effect of OL-HDF convection volume on patient survival.