ESTIMATION OF SMALL AND MIDDLE MOLECULE CLEARANCE FROM TREATMENT SETTINGS

Abstract

The aim of the current investigation was to compare values of whole blood clearance of small and middle molecules estimated by a mathematical model with clinical data obtained under conditions of pre- and postdilution hemodiafiltration (HDF). Input parameters of the model are blood flow, dialysate flow, filtration rate, patients' hematocrit and the characteristic dialyser constants, i.e. mass transfer area coefficient and sieving coefficient. Excellent agreement of in-vitro experimental data obtained in aqueous solution conditions with model predictions have been shown recently. To transfer the evaluated model for aqueous clearance to a model for whole blood clearance, the participation of red blood cells to solute transport was taken into account for the different solutes. Clinical clearance data of urea, creatinine, and beta-2-microglobulin obtained with dialysers FX60 and FX100 were compared to predictions from the mathematical model. Clearances of small molecules (urea and creatinine) were evaluated as whole blood clearance whereas beta-2-microglobulin was evaluated as plasma clearance. Model predictions showed good agreement with clinical data in the measured ranges of substitution rates up to 130 ml/min in postdilution HDF and up to 240 ml/min in predilution HDF. The model allows whole blood clearances resp. plasma clearances of small and middle molecules to be predicted from treatment settings with sufficient accuracy. For easy handling, it has been implemented as a software tool.