Solute transport in continuous arteriovenous hemodiafiltration: a new mathematical model applied to clinical data.

A mathematical model of continuous arteriovenous hemodiafiltration is presented, by which the diffusive mass transfer coefficient (Kd) for a solute may be calculated from blood, filtrate and dialysate flow rates and solute concentrations. The model was applied to clinical data obtained with 0.6-m2 AN69 capillary dialyzers that had been used for up to 5 days. The diffusive mass transfer coefficient proved to depend on dialysate flow rate. Furthermore, it was related to the membrane index of ultrafiltration, as measured in the clinic, and to the filter resistance to blood flow. Measurement of these filter characteristics allowed a reasonable prediction of solute clearance.