Supplementary Material for: Effect of reduced dialysate flow on dialysis adequacy: a pilot study

The standard dialysate flow (Qd) for hemodialysis (HD) is currently set at 500 mL/min. One potential, sustainable and cost-effective solution for eco-friendly HD may involve reducing Qd to limit waterwaste. However, the effect of reduced Qd on small and middle molecules (MM) removal remains to be investigated. In this prospective observational study,74 patients on different maintenance dialysis modalities with Qd set at 500 mL/min (Qd500), were assigned to receive Qd 400 mL/min (Qd400) for 3 months. Dialysis adequacy including small solutes removal and MM reduction ratio (RR) was evaluated at enrolment and after 3 months. Compared to Qd500, Qd400 after 3 months achieved similar spKt/V (1.41±0.30 vs 1.43±0.33, p=0.58), eKt/V, urea RR, creatinine RR and phosphate RR. Qd400 vs Qd500 provided significantly higher beta2-microglobulin RR [77.0 (71.4-81.7) vs 74.7 (68.4-79.4) %, p=0.009] and lower kappa FLC RR [54.2 (42.1-64.4) vs 57.6 (41.6-65.0) %, p=0.03], whereas myoglobin and lambda FLC RR were similar. Qd400 resulted in higher pre-dialysis urea (20.2±5.5 vs 18.2±6.2 mmol/L, p=0.002), creatinine (694.0±179.5 vs 665.6±220.4 µmol/L, p=0.029), beta2-microglobulin [26.5 (23.0-30.0) vs 23.5 (20.0-28.0) mg/L, p=0.0001] and myoglobin [174.0 (122.0-251.0) vs 159.5 (119.0-195.0) µg/l, p=0.033] levels. Pre-dialysis levels of albumin, potassium, bicarbonate, phosphate and calcium were similar between Qd400 and Qd500. Three months of Qd at 400 mL/min appears to provide similar small and MM removal, but with an increase in pre-dialysis urea, creatinine, beta2-microglobulin and myoglobin levels. Although this strategy could help preserving water, its potential impact on long-term clinical outcomes deserves further evaluation.