Plasma water filtration and lymphatic uptake during peritoneal dialysis

To clarify further the extent, pathways, and significance of convective transport during peritoneal dialysis, acute transport studies were conducted in which five continuous ambulatory peritoneal dialysis (CAPD) patients underwent 6 hr dialyses (2 L infusate with 2.25% dextrose) on 2 successive days, with multiple sampling of both blood and peritoneal dialysate. Concentrations of permeants (urea, creatinine, uric acid, beta 2 microglobulin, and apolipoprotein A) and a radiolabeled marker (125I-polyvinyl pyrollidone [PVP]) were determined at 20-30 min intervals in dialysate and every 90 min in plasma. Intraperitoneal volumes and lymphatic flows were calculated from rates of dilution and disappearance of 125I-PVP. Intratreatment lymphatic flow rate averaged 76 +/- 15 ml/hr. Although lower than observed in small animal models and reported by some clinical groups, this level of lymphatic drainage was still sufficient to decrease net patient weight loss by approximately 50% and to resorb approximately 15% of metabolites in the peritoneal cavity, independent of molecular weight. Transcapillary ultrafiltration ranged from 7.4 +/- 1.5 ml/min at 10 min into the exchange to 1.3 +/- 1.5 ml/min at 345 min. Reverse ultrafiltration, from the peritoneal cavity back through capillary vasculature to the patient, was not observed in any patient in this study.