Determining ultrafiltration properties of the peritoneum

Peritoneal solute reflection coefficients have previously been determined by simply comparing the time dependence of the solute concentration in the dialysis solution with that predicted by mathematical models. The present study theoretically examines the experimental conditions required to determine the solute reflection coefficient from the dependence of the dialysate concentration on time. Optimal experimental conditions are first derived using an approximate mathematical model that permits simple interpretation; these predictions are confirmed by numerical computation using a more rigorous model. It is demonstrated that the peritoneal solute reflection coefficient can be determined when solute transport is in the blood to dialysate direction only during a hypertonic exchange. When solute transport is in the dialysate to blood direction, the solute reflection coefficient can be determined using a hypotonic dialysis solution only for solutes that diffuse slowly across the peritoneum. Reliable determinations of the peritoneal solute reflection coefficient can only be obtained when using these experimental conditions.