Evaluation of Bidirectional Aluminum Transfer Across Hollow Fiber Dialyzers

Abstract

The ultrafiltrable fraction of plasma aluminum (UFA1) determined utilizing the hollow fiber dialyzer is variable and ranges from 10% to 50%. This extreme variability in UFA1, led us to examine the possibility of AI binding to the hollow fiber dialyzer. Ultrafiltrate of aqueous AI solutions was obtained by applying a negative pressure of 250 mm Hg to a hollow fiber dialyzer (TriEx-1). In the first of three experimental protocols, AI was measured before and after recirculation of solutions containing 344 to 9244 μg/L Al through a hollow fiber dialyzer until the entire volume was collected as ultrafiltrate. UFA1, ranged from 0.9% to 37.6% and did not correlate with the initial Al concentration. Total AI binding ranged from 42 μg to 1.3 mg. In the second, 16 L of aqueous AICI3 solution (n = 3), containing from 205 to 411 3g/L AI were passed through the blood compartment of a hollow fiber dialyzer. The percentage of UFA1, ranged from 4.1% to 17.3% during the first 20 minutes and 79.3% to 81.8% at 120 minutes. Finally, to investigate Al transfer from dialysate,16 L of deionized distilled water were passed through the blood compartment while 16 L of AICI3 solutions of 330 γg/L and 398 γg/L Al passed through the dialysate compartment. Samples were collected from blood and dialysate outflow ports every 20 minutes for 120 minutes. The transfer of AI from dialysate to blood compartment increased with time. However the concentration of Al at the blood outflow port never reached that at the dialysate outflow port. Furthermore, the decrement of dialysate Al across the dialyzer was greater than the increment of AI concentration in the blood compartment. These results indicate appreciable uptake of AI by the hollow fiber dialyzer from both dialysate and blood compartments. Thus, the use of the hollow fiber dialyzer to determine UFA1, or bidirectional AI transfer needs reevaluation.