Distinct Solute Removal Patterns by Similar Surface High-Flux Membranes in Haemodiafiltration: The Adsorption Point of View

Introduction: Haemodialysis (HD) allow depuration of uraemic toxins by diffusion, convection, and adsorption. Online haemodiafiltration (HDF) treatments add high convection to enhance removal. There are no prior studies on the relationship between convection and adsorption in HD membranes. The possible benefits conferred by intrinsic adsorption on protein-bound uraemic toxins (PBUTs) removal are unknown. Methods: Twenty-two patients underwent their second 3-days per week HD sessions with randomly selected haemodialysers (polysulfone, polymethylmethacrylate, cellulose triacetate, and polyamide copolymer) in high-flux HD and HDF. Blood samples were taken at the beginning and at the end of the treatment to assess the reduction ratio (RR) in a wide range of molecular weight uraemic toxins. A mid-range removal score (GRS) was also calculated. An elution protocol was implemented to quantify the amount of adsorbed mass (M-ads) for each molecule in every dialyser. Results: All synthetic membranes achieved higher RR for all toxins when used in HDF, specially the polysulfone haemodialyser, resulting in a GRS = 0.66 +/- 0.06 (p < 0.001 vs. cellulose triacetate and polyamide membranes). Adsorption was slightly enhanced by convection for all membranes. The polymethylmethacrylate membrane showed expected substantial adsorption of beta(2)-microglobulin (M-ads(HDF) = 3.5 +/- 2.1 mg vs. M-ads(HD) = 2.1 +/- 0.9 mg, p = 0.511), whereas total protein adsorption was pronounced in the cellulose triacetate membrane (M-ads(HDF) = 427.2 +/- 207.9 mg vs. M-ads(HD) = 274.7 +/- 138.3 mg, p = 0.586) without enhanced PBUT removal. Discussion/Conclusion: Convection improves removal and slightly increases adsorption. Adsorbed proteins do not lead to enhanced PBUTs depuration and limit membrane efficiency due to fouling. Selection of the correct membrane for convective therapies is mandatory to optimize removal efficiency.