Intraperitoneal fluid volume changes during peritoneal dialysis in the rat: indicator dilution vs. volumetric measurements.

In order to validate the single injection RISA (125I human serum albumin) indicator diluation technique for assessing the alterations in intraperitoneal (i.p.) dialysate volume (IPV) which occur vs. time [V(t)] during peritoneal dialysis (PD), the RISA dilution technique was compared to V(t) determinations using a direct volume recovery method in Wistar rats. Sixteen milliliters of either 1.36 or 3.86% Dianeal or 0.9% NaCl were used as dialysis fluids in exchanges lasting between 1 and 360 min. Approximately 4% (4.41 +/- 0.59 (SE; n = 8) for 1.36% Dianeal and 4.07 +/- 0.72 (n = 4) for 3.86% Dianeal) of the RISA dose given intraperitoneally was lost from the dialysate during the first 1(-1.5) min after instillation, conceivably due to rapid tracer adsorption to peritoneal surfaces. Following the initial instant tracer loss and RISA dilution due to a residual volume (3.07 +/- 0.18 ml; n = 12), RISA disappeared at a fractional rate (FDR) of 2.10 +/- 0.14 x 10(-3) min-1 and 1.67 +/- 0.09 x 10(-3) min-1, during the first 30 min for 1.36 and 3.86% Dianeal, respectively. The overall FDR was 1.33 +/- 0.10 x 10(-3) and 0.707 +/- 0.082 x 10(-3) min-1 for 1.36% Dianeal (0-150 min) and 3.86% Dianeal (0-360 min), respectively, while the overall (0-150 min) FDR for the NaCl exchanges was 1.40 +/- 0.21 x 10(-3) min-1. These values correspond to RISA clearances out of the peritoneal cavity (KE) of 29.2 +/- 1.8, 22.1 +/- 1.6, and 25.7 +/- 2.4 microliter x min-1 for 1.36 and 3.86% Dianeal and 0.9% NaCl, respectively. The KE value for 3.86% Dianeal was significantly (p < 0.05) lower than for the two dialysates with lower osmolality. The slightly enhanced FDR of RISA during the first 30 min was partly due to the presence of nonprotein-bound free iodine in the RISA preparation used, and also to an enhanced disappearance of albumin during the first portion of the dwell. V(t) data from individual experiments using the RISA dilution technique (RISA curves) were analyzed by computer-aided nonlinear least-squares regression analysis.(ABSTRACT TRUNCATED AT 400 WORDS)