ENHANCEMENT OF CONVECTIVE-TRANSPORT BY INTERNAL FILTRATION IN A MODIFIED EXPERIMENTAL HEMODIALYZER

Background. Hemodialysis using high flux membranes today is a commonly used therapy. The primary advantage is the larger spectrum of molecul es removed with these membranes, and the mechanism of removal is in pa rt due to a phenomenon of filtration and backfiltration along the leng th of the hollow fibers. We hypothesized that increasing the filtratio n and backfiltration fluxes by modifying the structure of the dialyzer could enhance the convective transport of various solutes. Methods. A modified high flux dialyzer was compared to the standard model in ter ms of pressure profiles, filtration-backfiltration rates and solute cl earances. The modification consisted on the placement of a O-ring arou nd the fiber bundle to create a resistance for the flow of the dialysi s solution external to the fibers. The study on filtration fluxes was carried out using a scintigraphic method previously described, and sol ute clearances were studied during ultrafiltration-controlled hemodial ysis sessions. Results. Utilizing a net filtration condition proximal to zero, the rates of proximal filtration and distal backfiltration in the experimental dialyzer were significantly enhanced in comparison w ith the standard dialyzer. The pressure drop in the dialysate compartm ent could be increased significantly, thus permitting an increase in t he positive transmembrane pressure in the first half of the dialyzer a nd a parallel increase in the negative transmembrane pressure in the s econd half of the dialyzer. This resulted in a significant enhancement of the convective transport of middle-large solutes as demonstrated b y the increase in vitamin B12 and inulin clearances. Conclusions. This approach suggests that changes in design of the dialyzer may affect i ts performance. The use of internal filtration is suggested to improve convection and dialyzer efficiency for larger solutes without the req uirement for high volumes of replacement fluid, as is the case for cur rent hemodiafiltration techniques.