Dialysate volume measurements required for determining peritoneal solute transport

Solute transport parameters for the peritoneal membrane have been previously determined using dialysate volumes measured by the indicator dilution method. Recent work has shown that the indicator dilution volume (IDV) exceeds true dialysate volume (TV) because the indicator or index solute is lost from the peritoneal cavity. A peritoneal transport model that includes significant solute loss from the peritoneal cavity is here described. Theory suggests that simultaneous measurements of both IDV and TV are required to calculate solute transport parameters for the peritoneal membrane when solutes are lost from the peritoneal cavity. The magnitude of systematic errors incurred by the use of either IDV or TV alone was determined in the calculated diffusive permeability-area product (PA) for creatinine during a two hour exchange in a rabbit model of peritoneal dialysis. IDV was measured using dextran (2 X 10(6) daltons) and TV by the dilution of multiple injections of Evans blue-albumin complex. Best estimates of PA using either or both volume measurements were determined in the blood to dialysate direction with isotonic (N = 9) and hypertonic (N = 7) solutions and in the dialysate to blood direction with isotonic (N = 4) and hypotonic (N = 4) solutions. Systematic errors in PA using either IDV alone or TV alone were small with either isotonic or hypertonic solutions but were increased with hypotonic solutions. Moreover, systematic errors were larger when using TV alone thaN IDV alone. When solute transport parameters for the peritoneal membrane are approximately determined employing only a single volume measurement, the use of IDV leads to less systematic error than TV.