Ultrafiltration Patterns during Automated Peritoneal Dialysis: Findings and Insights to Peritoneal Physiology

Key Points There is a consistent increase in ultrafiltration volumes achieved per cycle over the course of an automated peritoneal dialysis treatment session. A better understanding of intercycle ultrafiltration trends may inform prescription interventions that can improve patient retention. Surface area recruitment, mesenteric elasticity, and cumulative glucose concentration in the interstitium are possible explanations for our findings. Background With the growing use of automated peritoneal dialysis (APD), it is important to improve our knowledge of the clinical patterns and physiology of APD treatment sessions. The ultrafiltration (UF) achieved during each cycle of an APD treatment is assumed to be relatively linear if the delivered prescription is the same. We set out to determine whether that is indeed the case. Methods This is a single-center, cross-sectional study of patients on prevalent peritoneal dialysis (PD). All adult patients on APD (older than 18 years) who had been on PD for ≥3 months and ≥3 months on APD were included. Patients on continuous ambulatory PD or those with peritonitis within 3 months of the consent date were excluded. Individual treatment data from seven consecutive APD treatment sessions with consistent dialysate composition for each cycler exchange were collected for each patient. Results Thirty-nine patients met the inclusion criteria and were enrolled. The probability of yielding a positive UF was 48.9% for cycle 1, rising to 90.5% by cycle 6. Adjusting for average dextrose concentration, dwell time, fill volume, solute transfer rate, and number of cycles, we observed that cycles 2–6 achieved progressively higher UF volumes than cycle 1 ( P < 0.001). The first and last cycles demonstrated significantly different cycle UF volumes compared with a middle cycle (−230 and 277 ml, respectively, P < 0.001). Conclusions We observed a consistent increase in UF volumes achieved per cycle over the course of an APD treatment session with numerous clinical and physiologic implications. This provides the foundation for future studies investigating peritoneal intercycle variations and membrane physiology.