title: Peritoneal ultrafiltration: mechanisms and measures.
abstract: The net ultrafiltration during peritoneal dialysis equals the osmotic ultrafiltration minus the fluid loss. Fluid loss is made up primarily of hydrostatic pressure-driven convection to the tissues surrounding the peritoneal cavity and a lesser amount of lymph flow. The cellular and blood capillary sources of water are distributed in an interstitial matrix, which decreases the effective osmotic pressure in the vicinity of the microvasculature. The interstitial matrix makes the process of fluid removal far less efficient than it would be if the blood capillaries were actually in direct contact with the peritoneal fluid. Osmotically driven water transport occurs chiefly across the blood capillary endothelium into the interstitium and ultimately out into the peritoneal cavity. Aquaporin-1, water-only channels, are important for solute-free water transport from blood capillaries. There may also be specialized water channels in cells, but this likely provides only a small component of solute-free water to the peritoneal cavity. Signs of ultrafiltration failure include loss of solute-free ultrafiltration and general decrease in ultrafiltration below 400 ml with a 4-h dwell of hypertonic dialysate.
authors.affiliation: Department of Medicine, University of Mississippi Medical Center, Jackson, Miss., USA.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Flessner
mesh_terms: D006801:Humans; D006874:Hydrostatic Pressure; D009995:Osmosis; D010530:Peritoneal Dialysis; D010537:Peritoneum / Q000378:metabolism; D014462:Ultrafiltration