Quantifying Ultrafiltration in Peritoneal Dialysis Using the Sodium Dip

BACKGROUND: Volume overload is highly prevalent among patients treated with peritoneal dialysis, contributes to hypertension and is associated with an increased risk of cardiovascular events and death in this population. As a result, optimizing peritoneal ultrafiltration is a key component of high-quality dialysis prescription. Osmotic conductance to glucose reflects the water transport properties of the peritoneum, but measuring it requires an accurate quantification of ultrafiltration, which is often difficult to obtain due to variability in catheter patency and peritoneal residual volume.

METHODS: In this study, we derived a new mathematical model for estimating ultrafiltration during peritoneal dialysis, based on sodium sieving, utilizing a single measure of dialysate sodium concentration. The model was validated experimentally in a rat model of peritoneal dialysis, using dialysis fluid with two different sodium concentrations (125 mmol/l and 134 mmol/l) and three glucose strengths (1.5 %, 2.3% and 4.25%). Then, the same model was tested in a cohort of peritoneal dialysis patients to predict ultrafiltration.

RESULTS: In experimental and clinical conditions, the sodium-based estimation of ultrafiltration rate correlated with ultrafiltration rate measurements based on volumetry and albumin dilution, with a R2=0.35 and R2=0.76, respectively. Ultrafiltration based on sodium sieving was also successfully used to calculate osmotic conductance to glucose in the clinical cohort, with a Pearson r of 0.77.

CONCLUSIONS: Using the novel mathematical models in this study, the sodium dip can be used to accurately estimate osmotic conductance to glucose, and therefore, it is a promising measurement method for future clinical use.