INTRAPERITONEAL FLUID VOLUME CHANGES DURING PERITONEAL-DIALYSIS IN THE RAT - INDICATOR DILUTION VS VOLUMETRIC MEASUREMENTS

In order to validate the single injection RISA (I-125 human serum albu min) indicator diluation technique for assessing the alterations in in traperitoneal (i.p.) dialysate volume (IPV) which occur vs. time [V(t) ] during peritoneal dialysis (PD), the RISA dilution technique was com pared to V(t) determinations using a direct volume recovery method in Wistar rats. Sixteen milliliters of either 1.36 or 3.86% Dianeal(R) 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% Dia neal and 4.07 +/- 0.72 (n = 4) for 3.86% Dianeal) of the RISA dose giv en intraperitoneally was lost from the dialysate during the first 1(-1 .5) min after instillation, conceivably due to rag id tracer adsorptio n to peritoneal surfaces. Following the initial instant tracer loss an d RISA dilution due to a residual volume(3.07 +/- 0.18 ml; n = 12), RI SA disappeared at a fractional rate (FDR) of 2.10 +/- 0.14 x 10(-3) mi n(-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 +/- 0.1 0 x 10(-3) and 0.707 +/- 0.082 x 10(-3) min(-1) for 1.36% Dianeal (0-1 50 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 (K-E) of 29.2 +/- 1.8, 22.1 +/- 1.6, and 25.7 +/- 2.4 mu l x m in(-1) for 1.36 and 3.86% Dianeal and 0.9% NaCl, respectively. The K-E value for 3.86% Dianeal was significantly (p < 0.05) lower than for t he two dialysates with lower osmolality. The slightly enhanced FDR of RISA during the first 30 min was partly due to the presence of nonprot ein-bound free iodine in the RISA preparation used, and also to an enh anced disappearance of albumin during the first portion of the dwell. V(t) data from individual experiments using the RISA dilution techniqu e (RISA curves) were analyzed by computer-aided nonlinear least-square s regression analysis. The RISA curves seemed to overestimate the dire ctly measured V(t) curves when the RISA FDR was set constant during th e dwell at the overall (0-150 or 0-360 min) rate constants given above . A complete overlap of the RISA curves and V(t) curves was obtained, however, if the RISA FDR during the first 30 min was set nearly twice as high as during the rest of the dwell. It is concluded that the RISA technique can be used with reasonable accuracy for assessing V(t) cur ves after correcting for peritoneal losses of the mao romolecular trac er, the latter being enhanced during the first 30 min of the dwell. Fo r practical purposes, however, it may be sufficient to assume that the peritoneal tracer dose is lost in a monoexponential fashion. Not corr ecting for RISA adsorption and for an initially enhanced RISA disappea rance rate will lead to a slight overestimation of the intraperitoneal residual volume and of the initial UF rate.