Clinical importance of intraperitoneal pressure in peritoneal dialysis and measures to counteract its effect on net ultrafiltration.

Experiments in animals and in humans have shown that fluid loss from the peritoneal cavity to the body increases with large increments in the intraperitoneal hydrostatic pressure (IPP). We have demonstrated previously that much of this fluid loss occurs to the abdominal wall and is driven by the hydrostatic pressure gradient (i.p. pressure-skin pressure) that develops across the wall whenever therapeutic or pathologic volumes of fluid reside in the cavity. We hypothesized that eliminating the pressure difference across the wall by applying an equal and opposite pressure [abdominal counterpressure (ACP)] would decrease fluid movement into the wall and decrease fluid movement from the cavity. In addition, we hypothesized that net ultrafiltration or net fluid recovery would increase with ACP. To address these hypotheses, we dialyzed rats for 3 hours in the supine position at constant levels of IPP (4, 6, and 8 cmH2O) with isotonic or hypertonic dialysis solutions containing a protein marker of fluid movement. We measured total fluid loss, fluid marker concentration in the abdominal wall, and lymph flow. In separate animals, we repeated the experiments with ACP. Total fluid loss as determined by protein clearance and fluid marker deposition in the abdominal wall was decreased in all experiments. Lymph flow was unchanged by ACP. While ACP increased the net fluid recovery in isotonic dialysis, no change was observed in the hypertonic case. Analogous experiments were carried out in six dialysis patients with or without ACP during a 4-hour dialysis with 1.5% dextrose solution performed in the supine position at i.p. hydrostatic pressure of 4-6 cmH2O. No significant difference was noted in the measured net ultrafiltration between control and ACP studies. We conclude that the careful application of ACP does decrease fluid loss (particularly to the abdominal wall) during isotonic or hypertonic dialysis in the rat. However, ACP results in improved fluid recovery only with isotonic dialysis in rats and has no effect on the recovery of fluid during peritoneal dialysis in humans.