Unchecked Wall Vacuum Might Pose a Risk: An In Vitro Experimental Study on the Effects of Negative Wall Pressure on Suction Ureteral Access Sheaths—A PACE Group Study

Introduction: While safe positive intrarenal pressure (IRP) thresholds during retrograde intrarenal surgery (RIRS) are well known, negative outlet wall pressure applied to Flexible and Navigable Suction Sheaths (FANS) remains uncharacterized. Objective: To evaluate IRP dynamics under varying irrigation heights and negative suction pressures, providing foundational data to support evidence-based protocols in suction-assisted endourology. Materials and Methods: A silicone kidney model was instrumented with an 11–13Fr/46 cm FANS and a 7.5Fr single-use flexible ureteroscope. Real-time IRP was measured via pressure wire during four sequential phases: irrigation (30 seconds), suction (30 seconds), simulated channel blockage (90 seconds), and unblocking (5 seconds). Four experimental groups evaluated combinations of different irrigation heights (40 and 100 cmH 2 O) and negative pressures (−100 and −375 mmHg). Each combination was replicated three times, yielding 12 independent experiments. The primary outcome was the rate of IRP change (mmHg/s) during unblocking, and the secondary outcome was the maximum IRP observed during blockage. Data were analyzed using one-way ANOVA with Tukey’s post hoc test ( p < 0.05). Results: During unblocking, −375 mmHg suction produced significantly faster IRP reduction than −100 mmHg across all subgroups (mean differences 7.6–10.45 mmHg/s, p < 0.05). During blockage, 100 cmH 2 O irrigation generated significantly higher peak pressures than 40 cmH 2 O (mean differences 7.97–18.37 mmHg, p < 0.05). The combination of high irrigation pressure and high negative suction resulted in the most extreme and rapid pressure fluctuations, with changes occurring within fractions of 10-milliseconds. Conclusions: Negative outlet wall pressure significantly influences IRP dynamics during RIRS with FANS, producing rapid and extreme pressure changes. Pressure changes may occur on a timescale that could challenge manual recognition and corrective intervention. Standardized pressure monitoring and automated control systems might become a promising approach to ensuring patient safety during suction-assisted endourology.