Intraperitoneal hydrostatic pressure and ultrafiltration volume in CAPD

The intraperitoneal hydrostatic pressure (IPP) and overall ultrafiltration (UF) volume were measured in 34 patients after a 2-hour exchange with 2 L of dialysate containing 3.86% glucose. These patients had been treated with continuous ambulatory peritoneal dialysis (CAPD) on average for 26 +/- 20 months under stable conditions. The patients were at rest during the 2-hour exchange. The normal IPP measured with the patient lying completely flat was on inspiration (IPPinsp) 14 +/- 4 cm of water (cmH2O) and on expiration (IPPexp) 12 +/- 3 cm H2O, for an intraperitoneal volume of 2820 +/- 319 mL. The mean UF was 744 +/- 323 mL. The mean IPP (IPPmean), defined by (IPPinsp+IPPexp)/2, had a negative linear correlation to the UF volume (r = 0.66; p = 0.0001). The linear regression test showed that an increase of 1 cm H2O in the IPPmean reduced the overall UF volume by 70 mL in 2 hours. In conclusion, even though the UF is produced by the osmotic pressure of the dialysate, it is also influenced to a great extent by the intraperitoneal hydrostatic pressure, which should not be ignored.