Fluid transport and homeostasis in peritoneal dialysis.

Ultrafiltration failure is one of the main concerns for patients on long-term peritoneal dialysis. According to the three-pore model of peritoneal transport, peritoneal water flows via four pathways: ultrasmall pores, small pores, large pores and through peritoneal or lymphatic reabsorption. New methods that allow clinicians to identify the mechanisms behind disturbances in water transport can be applied in clinical practice. Small pore transport and free water transport can be estimated after a short 1-hour dwell with a glucose solution, without the need for an intraperitoneal volume marker. Until now, peritoneal reabsorption has been calculated using indirect and complicated methods. However, a simple, standardized method that is useful in clinical practice is needed. Ultrafiltration failure may be caused by rapid solute transport, slow solute transport, high peritoneal reabsorption and decreased free water transport (aquaporin failure). This article briefly discusses the clinical significance of disturbances in ultrafiltration, possible improvements in treatment options, and how to achieve or maintain fluid homeostasis.