Hemodialysis patients consume per year 18.720-26.208L of dialysis fluid (i.e. water). From an ecological point of view, the present study investigated whether reducing this water amount has an impact on the extraction and total solute removal of different uremic toxins. The efficiency of hemodiafiltration with a standard high-flux dialyzer is compared to hemodialysis with a medium cut-off dialyzer with a dialysate flow of either 700mL/min or 300mL/min.

Hemodialysis is currently performed with dialysate flows in the range 500 and 700mL/min respectively in hemodialysis and hemodiafiltration mode. With a standard daytime dialysis scheme of three times four hours a week, each patient consumes up to 360-504L dialysate per week or 18.720-26.208L per year.

From an ecological point of view, one can wonder whether patients can be dialyzed adequately enough using hemodialysis mode with a lower dialysate flow, and as such consuming less water.

Changing the mode from hemodiafiltration to hemodialysis mainly has an impact on the removal of larger toxins which benefit of the convective transport. Lowering dialysate flow in hemodialysis mode mainly has an impact on the removal of small water soluble toxins which are mainly removed by diffusion. For this transport, different parameters are important: blood and dialysate flow, dimensions of the membrane (surface area and thickness), fiber diameter, and extra-luminal space, and membrane porosity (Sieving coefficient). This also implies that, for the same blood and dialysate flow, the choice of the dialyzer will determine toxin transport. The use of a medium cut-off membrane with smaller and more open fibers might thus be more adequate in hemodialysis mode than a standard high-flux dialyzer with wider fibers.

The aim of this study is to quantify instant extraction and overall total solute removal of representative uremic toxins in hemodiafiltration with a standard high-flux hemodialyzer versus hemodialysis with a medium cut-off membrane, either with a standard or reduced dialysate flow.

Inclusion Criteria:

• stable chronic hemodialysis patient
• well functioning vascular access

Exclusion Criteria:

• active infection
• malignancies