Peritoneal physiology--impact on solute and fluid clearance.

A review is given on the physiology of peritoneal transport of solutes and fluid during peritoneal dialysis. Transport of low molecular weight solutes is dependent on the drained dialysate volume and the vascular peritoneal surface area. The transport of macromolecules is not only dependent on the surface area but progressively hindered the higher their molecular weight. Transport of solutes from the peritoneal cavity always exceeds transport in the other direction, caused by uptake in the lymphatics and the interstitium. Fluid transport is governed by transcapillary ultrafiltration and lymphatic absorption. The former is partly through aquaoporins when glucose-based dialysis solutions are used. The causes of ultrafiltration failure are reviewed, and the effects of the magnitude of the vascular peritoneal surface area on solute clearances and ultrafiltration, using various osmotic agents, are discussed.