From the Department of Pharmacology, Physiology and Neuroscience, University of South Carolina, Columbia, South Carolina.
ASAIO J. 2021 Jul 1;67(7):809-816. doi: 10.1097/MAT.0000000000001300.
To investigate mechanisms of acid-base changes during peritoneal dialysis (PD), a mathematical model was developed that describes kinetics of peritoneal bicarbonate, CO2, and pH during the dwell with both high and low lactate-containing dialysis fluids. The model was based on a previous modification of the Rippe 3-Pore model of water and solute kinetic transport across the peritoneal membrane during the PD dwell. A central feature of the present modification is an electroneutrality constraint on peritoneal-fluid ion concentrations, which results in the conclusion that peritoneal bicarbonate-concentration kinetics are entirely dependent on the kinetics of the other ions. This new model was able to closely predict peritoneal bicarbonate-concentration kinetics during the dwell. Predictions of total peritoneal bicarbonate-mass kinetics were greater than those of porous, transmembrane bicarbonate transport, suggesting that a portion of bicarbonate comes from CO2 transport, both porous and nonporous and then a partial conversion to bicarbonate. Fitting the model to experimental pH data during the dwell, required addition of a peritoneal CO2 mass-conservation constraint, coupled with the description for peritoneal bicarbonate kinetics. Predicted pH kinetics during the dwell, closely mimicked the experimental data. The conclusion was that the mechanisms describing peritoneal bicarbonate and pH kinetics during PD must include 1) electroneutrality of peritoneal fluid, 2) porous transport of bicarbonate and CO2, 3) nonporous transport of CO2, and 4) CO2 conversion to bicarbonate. These mechanisms are quite different and more complex than the bicarbonate-centered, lactate to acid-generation mechanisms previously proposed.
为了研究腹膜透析（PD）过程中酸碱变化的机制，我们建立了一个数学模型，该模型描述了高、低乳酸含量透析液在停留期间腹膜碳酸氢盐、CO2 和 pH 的动力学。该模型基于之前对 Rippe 3 孔模型的修改，该模型描述了 PD 停留期间腹膜膜上水和溶质动力学转运。目前修改的一个核心特征是对腹膜液离子浓度的电中性约束，这得出结论，腹膜碳酸氢盐浓度动力学完全取决于其他离子的动力学。这个新模型能够很好地预测停留期间腹膜碳酸氢盐浓度动力学。对总腹膜碳酸氢盐质量动力学的预测大于多孔、跨膜碳酸氢盐转运的预测，这表明碳酸氢盐的一部分来自 CO2 转运，既有多孔的也有无孔的，然后部分转化为碳酸氢盐。为了使模型适应停留期间的实验 pH 数据，需要添加腹膜 CO2 质量守恒约束，同时描述腹膜碳酸氢盐动力学。预测的停留期间 pH 动力学与实验数据非常吻合。结论是，描述 PD 期间腹膜碳酸氢盐和 pH 动力学的机制必须包括 1）腹膜液的电中性，2）碳酸氢盐和 CO2 的多孔转运，3）CO2 的无孔转运，以及 4）CO2 转化为碳酸氢盐。这些机制与以前提出的以碳酸氢盐为中心的乳酸生成酸生成机制非常不同，也更加复杂。
