Haemodiafiltration with sorbent-regenerated ultrafiltrate as replacement fluid: a multicenter study.

BACKGROUND Uncoated adsorbent charcoal may regenerate the ultrafiltrate suggesting its use as an endogenous substitution fluid. The objective of this study was to assess the safety and the long-term clinical results. METHODS Thirty-three chronic uraemic patients were dialysed for 1 year using two haemodialysers in series in order to separate convection from diffusion. At the outflow of the convective haemofilter, a cartridge containing 130 g of uncoated charcoal was inserted. The regenerated ultrafiltrate was then infused at the entrance of the diffusive dialyser. Ex vivo and in vitro studies were performed to analyse the adsorption characteristics and the release of aluminium, other trace elements, and microparticles. RESULTS Passage through the charcoal left urea, phosphate, potassium, calcium, and bicarbonate concentrations unchanged. Creatinine, uric acid and beta 2-microglobulin were almost completely absorbed by the charcoal. Aluminium release was dependent upon time of storage, as inferred from studies on inter-lot variability. Washing with bicarbonate buffer (pH 7.0) allowed reduction of aluminium levels to within the pharmacopoeia requirements for intravenous fluids. No significant pre- or post-charcoal differences were observed for several trace elements such as manganese, selenium, arsenic, cadmium, mercury, lead, chromium and zinc. Copper was completely retained in the charcoal. Regenerated ultrafiltrate infused at the entrance of the diffusive dialyser was free of microparticles, bacteria, and endotoxin. Clinical tolerance was excellent and blood pressure control satisfactory. A significant decrease in serum values of beta 2-microglobulin was observed at 6 and 12 months of treatment. CONCLUSIONS Reinfusion of ultrafiltrate through an uncoated charcoal cartridge proved to be a safe, well-tolerated and simple technique. Further potential benefits of regenerated ultrafiltrate may also include the maintenance of acid-base balance with reinfusion of endogenous bicarbonate.