Parameter mapping for the use of flexible and navigable suction sheath: an in vitro study

Retrograde intrarenal surgery (RIRS) is recommended for renal stones up to 20 mm. The Flexible and Navigable Suction Sheath (FANS) lowers intrarenal pressure (IRP), enhancing stone-free rates and reducing infectious risk. However, irrigation-suction parameters remain undefined. This study assesses settings across ureteroscope and FANS combinations to define parameters that maintain low IRP and optimal procedural performance. An in vitro experiment was performed using a kidney model and pressure sensor. Four ureteroscopes (6.3 Fr, 7.5 Fr, 8.4 Fr, 9.5 Fr) were evaluated with three FANS (10/12 Fr, 11/13 Fr, 12/14 Fr). Irrigation settings of 50, 100, and 150 mL/min were paired with suction pressures of - 150, - 200, - 250, and - 300 mmHg. Following a 1-min irrigation phase and 30 s of suction, pressure was recorded over 60 s at 0, 30, and 60 s. With the 6.3 Fr ureteroscope and 10/12 Fr FANS, 50 mL/min irrigation with -150 mmHg suction, and all suction combinations at 100-150 mL/min, maintained stable IRP; 11/13 Fr FANS produced collapse of the pelvicalyceal system (PCS). For the 7.5 Fr ureteroscope, the 10/12 Fr FANS allowed adequate IRP control at 50-100 mL/min across all suction pressures, while 150 mL/min exceeded 30 mmHg. With the 8.4 Fr ureteroscope and 10/12 Fr FANS, 50 mL/min with - 200 to - 300 mmHg suction kept IRP < 30 mmHg. The 11/13 Fr FANS preserved IRP at 150 mL/min with - 150 mmHg suction. For the 9.5 Fr ureteroscope, 11/13 Fr FANS maintained IRP < 30 mmHg at 50 mL/min with - 150 mmHg, and 100 mL/min with - 150 to - 250 mmHg. With 12/14 Fr FANS, only 150 mL/min with - 150 mmHg maintained IRP < 30 mmHg. FANS performance depends primarily on the balance between irrigation flow, suction pressure, and RESD. Appropriate ratio endoscope-sheath diameter (RESD) values and moderate irrigation-suction combinations allow optimal visibility and IRP control while preventing PCS collapse.