Peritoneal fluid kinetics: comparison between polyglucose solution and albumin solution

Polyglucose (PG) solution has been shown to be capable of inducing peritoneal ultrafiltration despite its hypo-osmolality. However, the mechanism of osmosis by PG is not clear. In this study, we compared the fluid kinetics of albumin (ALB) solution (thought to be an ideal solution that should induce ultrafiltration through colloid osmosis) and PG solution. A 4-hour dwell study with frequent sampling was conducted in Sprague-Dawley rats (six rats in each group). The study used 25 mL of dialysate buffer, 10% ALB dialysis solution, 15% ALB dialysis solution, 20% ALB dialysis solution, or 7.5% PG solution, with 131I albumin as an intraperitoneal volume marker. All solutions were prepared by adding ALB or PG to a base dialysis solution (without osmotic agent). The initial osmolality values of the five solutions were 250 mOsm/kg, 284 mOsm/kg, 300 mOsm/kg, 320 mOsm/kg, and 280 mOsm/kg, and the dialysate drainage volumes at 4 hours were 17.0 +/- 0.8 mL, 22.4 +/- 0.8 mL, 25.4 +/- 0.6 mL, 27.3 +/- 0.9 mL, and 26.3 +/- 0.6 mL (buffer, 10% ALB, 15% ALB, 20% ALB, and 7.5% PG groups, respectively). The higher initial osmolality in the ALB groups was partially due to the sodium content in the ALB powder. The intraperitoneal volume was decreasing in the 10% ALB group, rather stable in the 15% ALB group, but slowly increasing in the 20% ALB group. In the PG group, intraperitoneal volume decreased initially and then started to increase after 2 hours. This pattern was closely related to the increase in the dialysate osmolality (to higher than plasma level). At 4 hours, the dialysate osmolality was significantly higher (and higher than plasma level) in the PG group as compared to all the ALB groups. No differences in peritoneal fluid absorption rate were observed among the four treatment groups. In the 15% ALB and 20% ALB groups, the transcapillary ultrafiltration rate (Qu) was lower in the later part of the dwell than in the initial part of the dwell; in the PG group, the opposite pattern was observed. Our results suggest that the osmosis of albumin dialysis solution is different from the osmosis of polyglucose solution. Polyglucose solution induces net ultrafiltration only when the dialysate osmolality increase to higher than plasma level, suggesting that degradation of polyglucose may be important for effective ultrafiltration.