Polymers as Osmotic Agents for Peritoneal Dialysis

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Abstract
A sustained ultrafiltration during long-dwell peritoneal dialysis exchanges cannot be obtained with rapidly absorbable small molecular weight osmotic agents. Slowly absorbable synthetic poly ions tested on rats and rabbits yielded high and sustained ultrafiltration, but were toxic. Gelatin solutions were not toxic in acute rat studies and produced sustained ultrafiltration but were difficult to work with because of gelation. A review of the literature on the properties of gelatin derivatives, used as plasma substitutes, led us to believe that they may be also useful as osmotic agents in the peritoneal dialysis solutions. In the peritoneal dialysis system, hydrostatic pressure in the blood compartment cannot be readily manipulated. Therefore, traditionally a solute (osmotic agent) is added to the peritoneal dialysis solution to create an osmotic driving force. During the process of ultrafiltration (Figure I), the rate of ultrafiltration decreases with time due to dilution by ultrafiltrate and absorption of the osmotic agent. Thus, ultrafiltration will eventually cease after the dialysis solution is infused. The bigger the molecule of the osmotic agent, the longer ultrafiltration lasts because solute absorption through the peritoneal membrane is slower. Thus, to achieve sustained ultrafiltration, an osmotic agent with a bigger molecule would be more advantageous than the smaller one at comparable osmotic gradients.