Renal pelvic pressure drives fluid absorption in mini‐percutaneous nephrolithotomy: a quantitative model for absorption rate

To determine the quantitative impact of renal pelvic pressure (RPP) parameters on irrigation fluid absorption dynamics during mini-percutaneous nephrolithotomy (mPCNL). In this prospective observational study, 50 patients undergoing mPCNL were enrolled. Continuous synchronised RPP monitoring was performed using a calibrated pressure transduction system, while fluid absorption was quantified via a clinical grade endoscopic surgical monitor. Analytical approaches included Pearson correlation analysis and simple linear regression modelling to characterise pressure absorption dynamics. The median (interquartile range [IQR]) baseline, mean and maximum RPP values were 12.0 (10.3-14.8) mmHg, 16.7 (14.6-23.1) mmHg and 60.0 (35.0-67.3) mmHg, respectively. The median (IQR) fluid absorption was 625.5 (270.8-1296.5) mL, corresponding to an absorption rate of 838.0 (385.9-1349.4) mL/h. Mean RPP exhibited a significant positive correlation with absorption rate (Pearson R = 0.54, P < 0.001), with linear regression modelling demonstrating a 54.2-mL/h increase in absorption rate per 1-mmHg rise in mean RPP (R2 = 0.29, P < 0.001). Transient RPP spikes exceeding 100 mmHg occurred in 9% of cases, primarily linked to access sheath obstructions from calculus migration or blood clots. This study presents the first quantitative model identifying mean RPP as a critical predictor of irrigation fluid absorption during mPCNL. Acute pressure surges driven by sheath obstruction underscore the necessity for real-time RPP monitoring and optimised outflow strategies to minimise absorption-related risks.