Objectives: To compare the safety and effectiveness of a novel flexible vacuum-assisted ureteral access sheath (FV-UAS) and traditional ureteral access sheath (UAS) in simulating retrograde intrarenal surgery (RIRS). Materials and Methods: A manometric model was established in porcine kidneys to observe the change in intrarenal pressure (IRP) in the FV-UAS and traditional UAS groups at different irrigation fluid velocities of 30, 50, 80, and 100 mL/min. Establish a kidney stone model (with 0.2 g, dry, ≤5 mm stones) to simulate RIRS. A total of 20 porcine kidneys were randomly numbered from 1 to 20 (FV-UAS group, 1 - 10; traditional UAS group, 11 - 20). The stone volume clearance rate and operation time were compared between the two groups. ("Stonevolumeclearancerate=1-ResidualstonevolumePreoperativestonevolume×100%"). Stone volume was obtained by CT pre- and postoperatively. Results: FV-UAS can follow flexible ureteroscopy (f-URS) to cross the ureteropelvic junction (UPJ) and into the renal pelvis and calices. FV-UAS can actively make IRP <10 cmH₂O by adjusting the negative values at different irrigation fluid velocities. The mean residual stone volume of the FV-UAS vs traditional UAS groups was 33.7 vs 92.5 mm³ (p = 0.017). The mean stone volume clearance rates of the FV-UAS vs traditional UAS groups were 98.5% and 95.9%, respectively (p = 0.017). Seven cases achieved complete stone-free status in the FV-UAS group. All patients had residual fragments postoperatively in the traditional UAS group. Conclusions: FV-UAS can follow f-URS to cross the UPJ and into the renal pelvis and calices, avoiding the interference of UPJ in controlling IRP. FV-UAS can actively control the IRP to be reduced to the desired range by adjusting the negative value under any irrigation fluid velocity. FV-UAS close to the stone can achieve complete stone-free status in RIRS.

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