Sodium Chloride and Protein-Bound Toxin Removal in Hemodiafiltration

Eight maintenance dialysis patients will be enrolled in a prospective, randomized, crossover trial. HD will be compared with online pre-dilution HDF and HDF at increased plasma ionic strength. The ionic strength will be increased using an infusion fluid with hypertonic \[Na+\] by isovolumetric adding of a 5000 mmol/L NaCl solution. Blood and dialysate flowrates (250 and 575 mL/min, respectively), treatment time (240 min), and high-flux dialyser (surface area 2.1 sqm, PUREMA H) will be always kept identical. Anticoagulation with standard or fractionated heparin will be unchanged adopted from the patients' routinely used regimen. In both HDF modes, the infusion flow rate will be 125 mL/min. In HDF at increased plasma ionic strength, the infusate \[Na+\] will be adjusted to approach 240 mmol/L in plasma entering the dialyser and the dialysate \[Na+\] will be set at the technically feasible minimum of 130 mmol/L. Blood samples will be drawn from the arterial and venous blood lines and, if applicable, from the blood tubing connecting the two dialyzers at 0, 15, 30, 60, 120, 180, and 240 min. Samples at 240 min will be drawn after reducing the blood flow rate to 50 mL/min for 30 s and the dialysate flow turned off. A fraction of the spent dialysate will be continuously collected. Removal of the free and total fraction of para-cresyl sulfate and indoxyl sulfate will be determined by reduction ratios, dialytic clearances and mass in dialysate Hemocompatibility will be assessed by WBC and platelet counts, free Hb, LDH, C5a and TAT. \[Na+\] will be monitored in both arterial (i.e. before NaCl infusion) and venous blood of the extracorporeal system.