Estimating Transport in Peritoneal Dialysis Using Sodium Kinetics

Background: Reliable tests to assess membrane function in peritoneal dialysis are critically needed to individualize prescription, monitor membrane integrity, and improve outcomes of patients treated with peritoneal dialysis. Dialysate sodium kinetics could theoretically be used to estimate both osmotic water transport and solute diffusion across the peritoneal membrane. Here we tested the hypothesis that solute and water transport can be predicted solely from sodium kinetics. Methods: We derived a modified version of the three-pore model based on the Nernst-Planck equation, which accounts for the Gibbs-Donnan and plasma water effects. Computer simulations were compared with data from an experimental rat-model of peritoneal dialysis (n = 25), divided into six groups by dialysate glucose strength (1.5%, 2.3% and 4.25%) and fill volume (20 ml and 30 ml). The diffusion capacity of sodium and the area to diffusion length ratio were set as parameters and fitted to data consisting of sodium measurements during dialysis, using a non-linear least squares algorithm. Results: After running the regression, the model fit sodium data well (figure 1). Intraperitoneal fluid volume over time closely matched experimental data for all glucose strengths (figure 2). Predictions of the concentrations of 51Cr-EDTA over time in dialysate closely matched experimental data for most groups, but there was a slight deviation from datapoints in lower glucose strengths (figure 2). Conclusion: In conclusion, we demonstrate that sodium kinetics can predict changes in intraperitoneal volume and transport of small solutes, such as 51Cr-EDTA. This is in line with earlier results where sodium kinetics have been shown to closely correspond to changes in peritoneal fluid volume. The model should be further validated for other solutes, which might require adjustments of the model. Funding: Government Support – Non-U.S.Simulations (line) vs data (dots) for sodiumSimulations (line) vs data (dots) for Cr-EDTA and interaperitoneal volume