CLEARANCE RATIO - A POSSIBLE INDEX FOR PATIENT DIALYZABILITY?

Abstract

Purpose: Varying patient physiology may cause significant variations in eKt/V, increasing the risk for patients to receive an insufficient dose. For the quantification of these variations we evaluated a new index based on the ratio between whole body (Kwb) and effective (Keff) clearances. Methods: Whole body and equilibrated clearances, in contrast to dialyzer clearance, take into account the decreased efficiency of solute removal due to internal transport limitations in the body. Keff accounts only for the limitations due to recirculation. A DQM urea monitor (Gambro) in the spent dialysate line was used to derive the ratio Kwb/Keff directly from the dialysate urea concentration profile data. The plasma water concentration (Cpw), needed for the calculation of both clearances, is eliminated in the ratio. Kwb*Cpw is obtained as the product of the steady state slope (Kwb/V) of the dialysate urea curve and the initial urea mass (m0), with m0 determined from whole body urea kinetics as previously described (JASN 9:2118-2123, 1998). The product Keff*Cpw is the initial removal rate of urea, which on the dialysate side equals the product of dialysate flow and initial dialysate concentration. The clearance ratio was determined in 148 treatments of 106 patients at 14 clinics. The standard deviation of the ratio was computed for 26 patients who were dialyzed 2-4 times each. Results: The mean ratio was 0.89 (range 0.74-1.01) with 10% of the values below 0.82. These would require almost 10% increased dialysis time to reach “normal” delivered dose. The median of the standard deviations was only 0.02, showing the consistency of this index.