Effect of fluid supplementation and modality on peritoneal permeability characteristics in a rat peritoneal dialysis model

OBJECTIVE: Hemoconcentration may influence peritoneal permeability parameters in anesthetized animals without fluid supplementation. Therefore, the aim of this study was to investigate the effects of fluid supplementation on peritoneal permeability in an acute peritoneal dialysis model in anesthetized rats. DESIGN: To study the effect of fluid supplementation on peritoneal permeability characteristics, 24 anesthetized male Wistar rats were investigated in 3 groups during a 4-hour standardized peritoneal permeability analysis with a 3.86% glucose dialysis solution (SPARa). The groups included a control group with no fluid supplementation (None, n = 8), a group with continuous subcutaneous infusion of 0.9% NaCl 3 mL/hr (SC, n = 9), and a group with continuous intravenous infusion of 0.9% NaCl 3 mL/hr (IV, n = 7). Inflow, sampling, and outflow of the dialysate during the SPARa occurred via a cannula inserted intraperitoneally in the lower left quadrant of the abdomen. Blood was drawn at the end of the dwell. Baseline blood samples were obtained from six separate untreated rats. RESULTS: Plasma osmolality was significantly lower in the IV group (334+/-1.4 mOsm/kg) compared to the None group (348+/-0.7 mOsm/kg, p < 0.01), and not different from the SC group (335+/-6.4 mOsm/kg), but higher than baseline (314+/-5.3 mOsm/kg, p < 0.001). Urine production during the dwell was not different among the groups: None 10.6+/-5.3 mL; SC 8.0+/-6.0 mL; and IV 10.5+/-5.6 mL. Transcapillary ultrafiltration after 4 hours was significantly higher in the IV group (p < 0.05) compared to the other two groups. Net ultrafiltration and effective lymphatic absorption were similar in all groups. Mass transfer area coefficient of urea (MTACurea) was significantly greater in the IV group (155+/-23.2 microL/minute, p < 0.003), but not different between the None (118+/-16.2 microL/min) and SC (123+/-25.9 microL/min) groups. Correcting these for the baseline plasma concentration resulted in higher values, but the IV data remained greater than the SC and None groups (p < 0.01). The glucose absorption, albumin, and IgG clearances and the sieving of sodium were alike in all groups. CONCLUSION: It can be concluded that IV fluid supplementation is more effective in preventing dehydration than SC supplementation, and it enhanced some peritoneal permeability characteristics in anesthetized rats during a 4-hour investigation. It is therefore important to standardize fluid supplementation in experiments with anesthetized animals