Relationship between fill volume and transport in peritoneal dialysis

Introduction: Larger fill volumes in peritoneal dialysis (PD) typically improve small solute clearance and water removal, and vice versa – but the relationship between intra-peritoneal volume and the capacities for solute and water transport in PD has been little studied. Here, it is proposed that this relative relationship is described by a simple ratio (Volume_new/Volume_old)^2/3 up to a critical break-point volume, beyond which further volume increase is less beneficial in terms of transport. Method: To scrutinize this hypothesis, experiments were conducted in a rat model of PD alongside a retrospective analysis of clinical data from a prior study. Rats underwent PD with either three consecutive fills of 8+8+8 mL (n=10) or 12+12+12 mL (n=10), with 45-minute dwell time intervals. This approach yielded sixty estimations of water and solute transport, characterized by osmotic conductance to glucose (OCG) and solute diffusion capacities, respectively. Results: Comparative analysis of the predictive efficacy of the two models – the simple ratio versus the break-point model – was performed using Monte Carlo cross-validation. The break-point model emerged as a superior predictor for both water and solute transport, demonstrating its capability to characterize both experimental and clinical data. Conclusion: The present analysis indicates that relatively simple calculations can be used to approximate clinical effects on transport when prescribing a lower or higher fill volume to patients on PD.