What is the optimum dialysate flow in post-dilution online haemodiafiltration?

In post-dilution online hemodiafiltration (OL-HDF), the only recommendation concerning the dialysate, or dialysis fluid, refers to its purity. No study has yet determined whether using a high dialysate flow (Qd) is useful for increasing Kt or ultrafiltration-infusion volume.

Study the influence of Qd on Kt and on infusion volume in OL-HDF.

This was a prospective crossover study. There were 37 patients to whom 6 sessions of OL-HDF were administered at 3 different Qds: 500, 600 and 700ml/min. A 5008(®) monitor was used for the dialysis in 21 patients, while an AK-200(®) was used in 17. The dialysers used were: 20 with FX 800(®) and 17 with Polyflux-210(®). The rest of the parameters were kept constant. Monitor data collected were effective blood flow, effective dialysis time, final Kt and infused volume.

We found that using a Qd of 600 or 700ml/min increased Kt by 1.7% compared to using a Qd of 500ml/min. Differences in infusion volume were not significant. Increasing Qd from 500ml/min to 600 and 700ml/min increased dialysate consumption by 20% and 40%, respectively.

With the monitors and dialysers currently used in OL-HDF, a Qd higher than 500ml/min is unhelpful for increasing the efficacy of Kt or infusion volume. Consequently, using a high Qd wastes water, a truly important resource both from the ecological and economic points of view.