Peritoneal dialysate volume determined by indicator dilution measurements

Dialysate volume was simultaneously determined by two different indicator dilution technique as a function of dwell time in a rabbit model of peritoneal dialysis using isotonic, hypertonic and hypotonic solutions. After a single injection of a large molecular weight index solute (SIIS) to the dialysis solution at a known concentration, the first indicator dilution technique determined dialysate volume by the change in the index solute concentration. In the second technique, dialysate volume was determined after multiple injections of a different index solute (MIIS) by measuring the change in concentration of the index solute two minutes after its injection into the dialysis solution. The volumes determined by SIIS were similar during isotonic, but larger during both hypertonic and hypotonic exchanges, than those determined by MIIS. Drained volume was dependent upon the peritoneal catheter used, was not different from that determined by MIIS, but was significantly smaller than that determined by SIIS. The present results suggest that systematic errors in volume measurements when using indicator dilution result from the loss of the index solute from the peritoneal cavity and are greater for SIIS than for MIIS. A model for fluid transfer during peritoneal dialysis showed that dialysate volumes determined by SIIS were useful, however, when estimating the rate of fluid movement across the peritoneal membrane.