The use of polyelectrolytes as osmotic agents for peritoneal dialysis.

Various small and large molecules have been studied as osmotic agents to replace dextrose in peritoneal dialysis. Macromolecules are attractive because of their slow absorption from intraperitoneal solutions; however, it has been assumed that they are only marginally effective as osmotic agents unless they function as polyelectrolytes at physiological pH. In experimental exchanges conducted in rats we measured volume changes induced by Gelifundol (5.5% oxypolygelatin) and Ringers lactate to which was added either nothing, 4.25% dextrose, or 5% albumin. In the control exchanges using Ringers lactate, intraperitoneal fluid volume remained unchanged for eight hours. The volume changes induced by 4.25% dextrose were complete within two hours and resulted in a two-thirds increase over the amount of fluid administered. In both series in which polyelectrolytes were used volume transport was sustained throughout an eight hour dwell. With 5% albumin the total increase in fluid volume was about 40% of that installed, while Gelifundol caused fluid volume to double. Qualitatively similar results were obtained in transport studies conducted in vitro. Physical studies of the oxypolygelatin solutions indicated that the fixed charges per liter were comparable to those in the albumin solutions. Thus the different volume transport the two proteins induced could not be attributed to Donnan effects. However, since the molecular weight of albumin is triple that of Gelifundol the van't Hoff pressures of the two macromolecules can explain the observed differences in volume transport. These results suggest that neutral macromolecules deserve further study as potential osmotic agents for peritoneal dialysis.

Errors in estimates of peritoneal fluid volume.

Inherent limitations in the suitability of drainage volumes for monitoring intraperitoneal fluid volume have resulted in the frequent use of indicator dilution techniques, but little attention has been given to confirming the adequacy of the estimates that volume markers provide. In a series of experimental exchanges in rats, volume estimates were compared based on the dilution of blue dextran and hemoglobin with direct collections of surgically exposed intraperitoneal fluid. Significant systematic and random errors in the indicator dilution volume estimates were observed. The systematic errors appeared to be due to the rapid removal of a fixed amount of marker from peritoneal fluid, while the random errors were caused by the rapid appearance of a variable amount of endogenous chromogen. The behavior of the markers observed in this study was not consistent with the assumptions commonly used to analyze volume transport in peritoneal dialysis.