Is Adapted APD Theoretically More Efficient than Conventional APD?

Abstract

Background A modified version of automated peritoneal dialysis (APD) using not only variable dwell times but also variable fill volumes has been tested against conventional APD (cAPD) with fixed dwell volumes in a randomized controlled clinical study. The results have indicated that the modified schedule for APD, denoted adapted APD (aAPD), can lead to improved small solute clearances, and, above all, a markedly increased sodium removal (NaR). To theoretically test these results, we have modeled aAPD vs cAPD in computer simulations using the 3-pore model (TPM). Methods The TPM, modified by including a transient, initial inflation of small solute mass transfer area coefficients (PS values), was employed. For simulations of osmotic ultrafiltration (UF), the TPM uses a constantly inflated value for PS for glucose and also a reduced value for PS for Na+, setting the peritoneal lymphatic reabsorption term at 0.3 mL/min. The simulations were performed by assuming that increases in intraperitoneal hydrostatic pressure (IPP) are transmitted to the capillary level ( via vein compression) and therefore do not significantly affect the Starling balance. Furthermore, the effective peritoneal surface area (A) was set to be variable as a function of intraperitoneal volume (IPV). Results The simulations demonstrated a minor improvement of small solute clearances (∼0.7 – 1.6%) and a very small improvement of UF and NaR in aAPD compared to cAPD. Conclusions Due mainly to the increased fill volumes in 3 out of 5 dwells in aAPD, this modality caused minor increases in small solute clearances and marginal effects on UF and NaR. The computer simulations point to a need for accurate sodium determinations in aAPD, considering all the methodological problems and pitfalls relevant to determining dialysate Na+ concentrations and peritoneal sodium mass balance.