The influence of peritoneal surface area on dialysis adequacy.

In children, the prescription of peritoneal dialysis is based mainly on the choice of the peritoneal dialysis fluid, the intraperitoneal fill volume (mL/m2 body surface area (BSA)], and the contact time. The working mode of the peritoneal membrane as a dialysis membrane is more related to a dynamic complex structure than to a static hemodialyzer. Thus, the peritoneal surface area impacts on dialysis adequacy. In fact, the peritoneal surface area may be viewed as composed of three exchange entities: the anatomic area, the contact area, and the vascular area. First, in infants, the anatomic area appears to be two-fold larger than in adults when expressed per kilogram body weight. On the other hand, the anatomic area becomes independent of age when expressed per square meter BSA. Therefore, scaling of the intraperitoneal fill volume by BSA (m2) is necessary to prevent a too low ratio of fill volume to exchange area, which would result in a functional "hyperpermeable" peritoneal exchange. Second, the contact area, also called the wetted membrane, is only a portion of the anatomic area, representing 30% to 60% of this area in humans, as measured by computed tomography. Both posture and fill volume may affect the extent of recruitment of contact area. Finally, the vascular area is influenced by the availability of both the anatomic area and the recruited contact area. This surface is governed essentially by both peritonealvascular perfusion, represented by the mesenteric vascular flow and, hence, by the number of perfused capillaries available for exchange. This vascular area is dynamically affected by different factors, such as composition of the peritoneal fluid, the fill volume, and the production of inflammatory agents. Peritoneal dialysis fluids that will be developed in the future for children should allow an optimization of the fill volume owing to a better tolerance in terms of lower achieved intraperitoneal pressure for a given fill volume. Moreover, future peritoneal dialysis fluids should protect the peritoneal membrane from hyperperfusion (lower glucose degradation products).