An hypothesis to explain the ultrafiltration characteristics of peritoneal dialysis.

We present an hypothesis that could account for many characteristics of ultrafiltration and solute movement during peritoneal dialysis. The hypothesis describes transcapillary ultrafiltration and can account for (1) the osmotic effectiveness of rapidly absorbed glucose, (2) small solute sieving in a system permitting protein loss, (3) functional estimates of effective pore sizes as low as 11 A for urea and as high as 62 A for proteins from hydrodynamic analyses, (4) isolated loss of ultrafiltration without loss of clearance, (5) decreased ultrafiltration with decreased clearances, and (6) increased ultrafiltration with decreased clearances. Mechanisms for fluid movement from the peritoneal interstitium into the peritoneal cavity may involve both hydrostatic and osmotic pressure. Interstitial water pathway dimensions, interstitial gel surface charges, mesothelial cell surface charges, and transmesothelial-cell water movement might also account for sieving effects during peritoneal ultrafiltration.