Dynamic changes of the total pore area available for peritoneal exchange in children

The most important of the parameters that describe exchange across the peritoneal membrane is the total pore area over diffusion distance (A(0)/Deltax). It determines the rate of diffusion and mainly seems to reflect the number of capillaries available for exchange. In the present study, a simplified three-pore analysis was used to estimate A(0)/Deltax from peritoneal equilibration tests. Two groups of children (mean age, 9.5 yr) who were on chronic peritoneal dialysis underwent studies with peritoneal equilibration tests. In the first group of children, three levels of fill volumes were used in each patient. In the second group of patients, the effects of posture and dwell time were analyzed from four consecutive peritoneal dialysis samples obtained after 15, 30, 60, and 90 min. As the fill volume was raised from 800 to 1400 ml/m(2) BSA, the steady-state A(0)/Deltax increased significantly by 21%, i.e., from 19,900 +/- 1200 to 24,000 +/- 1450 cm(2)/cm per 1.73 m(2) (n = 8). A further increase to 2000 ml/m(2) did not result in any change of A(0)/Deltax. Moreover, steady-state A(0)/Deltax fell significantly when the patients were standing, 21,900 +/- 1400 compared with 29,400 +/- 1330 cm(2)/cm per 1.73m(2) (n = 6) obtained in the supine position. There was a transient (<30 min) increase in A(0)/Deltax initially during the dwell, probably reflecting vasodilation and recruitment of capillaries. It is concluded that factors such as the intraperitoneal fill volume, posture, and dwell time all dynamically affect the total pore area available for exchange.