Use of the Ultrafiltrate Obtained in Two-Chamber (Pfd) Hemodiafiltration as Replacement Fluid. Experimental ex vivo and in Vitro Study

Abstract

PFD (Paired Filtration Dialysis) is the only hemodiafiltration (HDF) technique in which the ultrafiltrate (UF) is continuously available not mixed with the dialysate. As with all convective or prevailingly convective techniques, a replacement fluid is necessary in an amount equal to the difference between the UF and the desired weight loss. This replacement fluid (R) must have an adequate electrolytic balance (Na⁺, Ca⁺⁺, and buffer), and must be sterile and pyrogen-free. Using an uncoated adsorbent charcoal cartridge, we “regenerated” the UF obtained in PFD, eliminating the small (except for urea, which was later eliminated by diffusion in the dialyzing section of the PFD system) and the medium-to-large molecules (vit B12 and myoglobin in vitro and beta-2-microglobulin (B2m) and (hANP) in vivo), but not the electrolytes and the endogenous bicarbonate, so as to verify its possible use as R. This technique, experimentally performed in 12 patients under HDF treatment with standard PFD, with a total mean UF of 9650 ± 875 ml and the use of 130 g of uncoated charcoal, produced a solution with the following composition: Na⁺ 135.4 ± 2.4 mmol/l, K⁺ 3.4 ± 1.23 mmol/l, Ca⁺⁺ 1.18 ± 0.14 mmol/l, HCO₃^- 26.7 ± 2.3 mmol/l, phosphates 2.88 ± 0.81 mg/dl, urea 63 ± 14 mg/dl, creatinine 0.08 ± 0.02 mg/dl, uric acid 0.05 ± 0.0 mg/dl, beta-2 microglobulin 0.5 ± 0.5 mg/l, and hANP 4.15 ± 5 pg/l. By integration with electrolytes (Na⁺, Ca⁺⁺) and buffer, and changes in the composition of the dialysate, and considering that the K⁺ and phosphates, and urea, can all be removed by diffusion in the dialyzing section, PFD can be done using in its “regenerated” ultrafiltrate as an “endogenous” replacement fluid.