Handle with care: ureteral access sheath positioning modulates intrarenal pressure-insights from an EAU endourology ex vivo study using four ureteroscope sizes.

PURPOSE: To evaluate the impact of position of the external end of the ureteral access sheath (UAS) on the regulation and management of intrarenal pressure (IRP) using 4 different scopes with varying working channel diameters. MATERIALS AND METHODS: An ex-vivo study evaluating four single-use flexible ureteroscopes was performed. The IRP measurements were performed with the flexible ureteroscopes only and with 10/12Fr and 12/14Fr UASs together with flexible ureteroscopes. The main variable of interest was the position of the external end of the UAS termed as high (30 cm above), middle (15 cm above) and low (at the kidney level). RESULTS: The highest maximal IRPs were recorded with the 9.2Fr PU400A Pusen scope in all settings. Minor differences were noted between the measurements with no UAS and with UAS in high position. Decreasing the end position of the UAS from high to middle and low resulted in significant decline of IRPs, 33.3% and 66.7% for 7.5Fr and 9.0Fr HugeMed (HU30S and HU30) and 7.5Fr Pusen (PU3033AH), and 25.0% and 55.0% for 9.2Fr (PU400A) ureteroscopes, respectively. CONCLUSION: From our experiments, surgeons should try to always maintain the scope and sheath in position 1 which is flat and in line with the table / patient. Higher intrarenal pressures are expected with large working channel scopes (5.1Fr vs. 3.6Fr) even following the recommended ratio of endoscope-sheath diameter of 0.75 in all positions but lowest in low position. These findings underscore the importance of position of external end of the UAS in regulating IRPs during RIRS.