Optimization of dialysate flow in on-line hemodiafiltration

Currently, on-line hemodiafiltration (HDF-OL) is the most effective technique. Several randomized studies and meta-analyses have shown a reduced mortality and a direct association with convective volume has been reported. At present, it has not been established if an increased dialysate flow (Qd) results in improved results in terms of convective and depurative efficiency. We aim at assessing the effects of Qd variations on convective volume and its depurative capacity in patients on HDF-OL.

A total of 59 patients (45 men and 14 women) from a HDF-OL programme in which a monitor 5008 Cordiax with self-replacement was used, were enrolled. Patients were assessed in 5 sessions with post-dilutional HDF-OL, using helixone-based dialyzers, with only Qd being changed (300, 400, 500, 600 and 700ml/min). Serum levels of urea (60Da), creatinine (113 Da), β2-microglobulin (11,800Da), myoglobin (17,200Da) and α1-microglobulin (33,000Da) were measured at the beginning and at the end of each session, in order to estimate the percent reduction of such solutes.

An increased dialysate volume per session was observed, from 117.9±6.4 L with Qd 300ml/min to 232.4±12 L with Qd 700ml/min. No changes were found in replacement volume or convective volume. Regarding diffusion, Qd increase was associated to a significantly increased dialysis dose, with an increased Kt from 68±6.9 L with Qd 300ml/min to 75.5±7.3 L with Qd 700ml/min (p<0,001), and a gradually increased percent reduction in urea associated to increased Qd with significantly lower levels being found with Qd 300ml/min. No changes were found in other measured substances.

Qd variations in HDF-OL do not change convective volume. A higher Qd was associated to a slightly increased urea clearance with no change being observed for medium and large molecules. Qd optimisation to the minimal level assuring an adequate dialysis dose and allowing water and dialysate use to be rationalised should be recommended.