How low can we go with the dialysate flow? A retrospective study on the safety and adequacy of a water-saving dialysis prescription

Green nephrology encompasses all initiatives in kidney care that have a positive impact on climate and environment. To prepare the dialysate at least 120 liters of water are needed for one four-hour session with a dialysate flow (Qd) set at 500 ml/min. Lower dialysate flow rate is associated with a significant reduction in the amount of water used. The aim of this study was to check whether change of Qd from 500 ml/min to 300 ml/min has a significant impact on dialysis adequacy. The study was a retrospective analysis. Due to administrative issues a satellite dialysis center reduced dialysate flow to 300 ml/min for a month. The center again increased Qd to 500 ml/min. We analyzed laboratory data from 3 months before dialysate flow reduction, in the month with reduced Qd to 300 ml/min, and from 3 months thereafter with Qd set at 500 ml/min. 24 people were included in the final analysis. There were no significant changes in URR caused by lower rate of Qd (64.50 [61.75-71.00] vs 67.00 [63.00-72.25] vs 69.00 [63.75-72.25], ANOVA F(2,46)=0.71, p=0.50). Similarly, hemodialysis adequacy expressed by Kt/V did not differ at any Qd (1.23 [1.12-1.41] vs 1.25 [1.18-1.40] vs 1.35 [1.19-1.48], ANOVA F(2,46)=2.51, p=0.09). There was a small but statistically significant increase in mean predialysis K with lower Qd: (K = 5.18 (95%CI 4.96-5.44) vs. 5.46 (95%CI 5.23-5.69) vs. 5.23 (95%CI 4.99-5.47) mmol/l at Qd=500, 300, and 500 ml/min, respectively, p=0.039.) Reduction in dialysate flow rate to 300 ml/min seems safe and does not cause any short-term negative effects in this small study. Thus, we might be able to achieve a similar therapeutic effect saving water consumption. Larger, long-term studies incorporating patient reported outcome measures are needed to confirm the efficacy of this approach.