Optimal placement of ureteral access sheath in retrograde intrarenal surgery

Abstract Purpose : To explore the optimal location of ureteral access sheath (UAS) in retrograde intrarenal lithotripsy (RIRS). Materials and methods: RIRS model was built by AutoCAD 2011 software, and imported COMSOL 5.6 software to computer simulation. An RIRS model was constructed in vitro to analyze the distribution pattern of stone fragments, and compare the weight of stone fragments carried out by the irrigation fluid when the UAS is in different positions. Results: Computer simulation showed that the highest flow of irrigation fluid was in the channel of flexible ureteroscopy (f-URS) and in the lumen of UAS. From the f-URS to the renal collection system and then to the UAS, the velocity of irrigation fluid changes gradually from high-flow to low-flow and then to high-flow. When the f-URS and the UAS are at the same level, the irrigation fluid is always at a state of high flow during the process from f-URS to UAS. When the f-URS and the UAS are at the same level, it can increase the local intrarenal pressure (IRP) at the front of f-URS. The stone fragments are mainly sediment in the low-flow region of irrigation fluid. More stone fragments could follow the irrigation fluid out of the body when the tip of f-URS and the tip of UAS are at the same level ( P ＜0.001). Conclusions : The UAS should be brought closer to the stone in RIRS. And more stone fragments can be taken out of the body by the effect of irrigation fluid.