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

Objective: Hemoconcentration may influence peritoneal permeability paramete rs in anesthetized animals without fluid supplementation. Therefore, the ai m of this study was to investigate the effects of fluid supplementation on peritoneal permeability in an acute peritoneal dialysis model in anesthetiz ed rats. Design: To study the effect of fluid supplementation on peritoneal permeabi lity characteristics, 24 anesthetized male Wistar rats were investigated in 3 groups during a 4-hour standardized peritoneal permeability analysis wit h 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 co ntinuous intravenous infusion of 0.9% NaCl 3 mL/hr (IV, n = 7). Inflow, sam pling, and outflow of the dialysate during the SPARa occurred via a cannula inserted intraperitoneally in the lower left quadrant of the abdomen. Bloo d was drawn at the end of the dwell. Baseline blood samples were obtained f rom 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), a nd not different from the SC group (335 +/- 6.4 mOsm/kg), but higher than b aseline (314 +/- 5.3 mOsm/kg, p < 0.001). Urine production during the dwell was not different among the groups: None 10.6 +/- 5.3 mt; SC 8.0 +/- 6.0 m t; and IV 10.5 +/- 5.6 mt. 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 signi ficantly greater in the IV group (155 +/- 23.2 <mu>L/minute, p < 0.003), bu t not different between the None (118 +/- 16.2 <mu>L/min) and SC (123 +/- 2 5.9 muL/min) groups. Correcting these for the baseline plasma concentration resulted in higher values, but the IV data remained greater than the SC an d None groups (p < 0.01). The glucose absorption, albumin, and IgG clearanc es and the sieving of sodium were alike in all groups. Conclusion: It can be concluded that IV fluid supplementation is more effec tive in preventing dehydration than SC supplementation, and it enhanced som e peritoneal permeability characteristics in anesthetized rats during a 4-h our investigation. It is therefore important to standardize fluid supplemen tation in experiments with anesthetized animals.