A new method to evaluate the local clearance at different annular rings inside hemodialyzers

Recent research indicated that the dialysate flow distribution inside a hemodialyzer was not uniform ("channeling" of the dialysate flows). However, effect of the channeling on the solute clearance has not been directly and quantitatively examined. In this report, a novel experiment approach is presented to test the hypothesis that hollow fibers in different regions within a given hemodialyzer may contribute differently to the solute clearance. Water solution with urea (molecular weight 60) and creatinine (molecular weight 113) were made as "blood," and pure water was used as dialysate. Two high flux dialyzers, dialyzer A (cellulose triacetate) and dialyzer B (polyethersulfone), were used in this study. The hollow fiber potting area at the blood inlet of a dialyzer was divided into equal area concentric rings. In each experiment, only one of the rings was open for blood flow, and the other rings were blocked by epoxy. The "blood" was pumped at 120 ml/min while the dialysate flow rate (Qd) varied at 500, 800, and 1,000 ml/min, respectively. The solute clearance with a specific ring open (local clearance) was determined by measuring solute (urea/creatinine) concentration at the "blood" inlet and outlet. For dialyzer A, local clearance of urea and creatinine were significantly higher in the outer ring than in the inner ring. With increasing Qd, local solute clearance increased significantly for all rings. For dialyzer B, at any given Qd, solutes local clearance also increased from the inner to outer rings. In comparison, the effect of increasing Qd on solute clearance was greater for dialyzer B than for dialyzer A. In conclusion, using the new experimental method, the authors quantitatively evaluated the solute clearance contributed by the hollow fibers at different locations (concentric rings) in dialyzers. Hollow fibers at different locations did contribute differently to the solute clearance, which may be caused by the channeling of dialysate flow. A careful design of the dialyzer to minimize the channeling is needed.