Relationship between body size, fill volume, and mass transfer area coefficient in peritoneal dialysis

A peritoneal dialysate fill volume of 2 L has become the standard of clinical practice, but the relationships between body size, fill volume, and mass transfer area coefficient (KoA) have not been well established. These relationships were studied in 10 stable peritoneal dialysis patients who underwent six peritoneal equilibration studies (2 h each) at fill volumes of 0.5, 1, 1.5, 2, 2.5, and 3 L. The concentration-time profiles for urea, creatinine, and glucose were measured at each fill volume, and residual volumes were calculated from the preceding dwell period. A modified Henderson equation was used to calculate the KoA for the three solutes as a function of fill volume. By normalizing the KoA for each solute to the value at 2 L, the data for all three solutes collapsed onto the same trend line when plotting the normalized KoA versus dialysate volume. Between 0.5- and 2-L fill volumes, the average normalized KoA increases in an almost linear fashion, its value almost doubling over this range. Between 2- and 3-L fill volumes, there is less than a 10% change in the normalized KoA. However, fill volumes for peak urea KoA were found to increase with increasing body surface area (R = 0.76), being around 2.5 L for an average-sized patient and increasing to between 3 and 3.5 L for body surface areas > 2 m2. To maximize solute transport, these relationships between body size, volume, and KoA should be considered when choosing fill volumes for continuous ambulatory peritoneal dialysis and automated peritoneal dialysis and when deciding reserve and tidal volumes for tidal peritoneal dialysis.