Optimizing peritoneal dialysis prescription for volume control: the importance of varying dwell time and dwell volume.

Not only adequate uremic toxin removal but also volume control is essential in peritoneal dialysis (PD) to improve patient outcome. Modification of dwell time impacts on both ultrafiltration (UF) and purification. A short dwell favors UF but preferentially removes small solutes such as urea. A long dwell favors uremic toxin removal but also peritoneal fluid reabsorption due to the time-dependent loss of the crystalloid osmotic gradient. In particular, the long daytime dwell in automated PD may result in significant water and sodium reabsorption, and in such cases icodextrin should be considered. Increasing dwell volume favors the removal of solutes such as sodium due to the increased volume of diffusion and the recruitment of peritoneal surface area. A very large fill volume with too high an intraperitoneal pressure (IPP) may, however, result in back-filtration and thus reduced UF and sodium clearance. Based on these principles and the individual transport and pressure kinetics obtained from peritoneal equilibration tests and IPP measurements, we suggest combining short dwells with a low fill volume to favor UF with long dwells and a large fill volume to favor solute removal. Results from a recent randomized cross-over trial and earlier observational data in children support this concept: the absolute UF and UF relative to the administered glucose increased and solute removal and blood pressure improved.