The effect of dialysate osmolarity on ultrafiltration and vascular refilling rate

The osmotic gradient is the main driving force for ultrafiltration (UF) in continuous ambulatory peritoneal dialysis (CAPD). Depending on glucose absorption, its changes over a period of time could influence the plasma refilling rate. The aim of this study was to evaluate the influence of changes in the plasma refilling rate obtained by dialysates of different osmolalities upon the rate of UF. Stable CAPD patients were studied twice during a 4-hour exchange 2 weeks apart with dialysate containing 1.5% and 4.25% glucose, respectively. UF was estimated by the autologous hemoglobin dilution method every 30 minutes. Hematocrit and colloidosmotic pressure (COP) decrease when using 1.5% glucose dialysate, reflecting a rise in plasma water mediated by the plasma refilling rate. This water shift is greater than the osmotic gradient generated between peritoneal and intravascular compartments as reflected by a low UF rate. However, when the osmotic gradient increases by means of 4.25% glucose dialysate, the plasma refilling rate is efficiently counter-balanced by UF.