Computational fluid dynamics analysis of the effect of ureteral access sheath positioning on stone clearance rates.

Standardized protocols for optimal ureteral access sheath (UAS) positioning during flexible ureterorenoscopy (f-URS) lithotripsy have yet to be established. This study utilizes computational fluid dynamics (CFD) techniques to analyze the impact of varying UAS positions on stone clearance rates, aiming to identify the optimal UAS position for enhanced stone fragment evacuation. Various f-URS models were created using ANSYS SpaceClaim software. These models were then imported into ANSYS Fluent for meshing and computational simulation. The study evaluated the impact on stone clearance rates as the UAS was incrementally advanced towards the distal end of the f-URS, also observing the effects on local irrigation flow velocity at different UAS positions. Three models were constructed to simulate stone positions within the renal pelvis, lower calyx, and middle calyx. Each model generated 80 stone particles. In the middle calyx model, the numbers of particles evacuated were 32, 53, 58, and 67 for UAS positions A, B, C, and D, respectively. In the lower calyx model, particle clearance was 15, 21, 37, and 46 for UAS positions A, B, C, and D, respectively. In the renal pelvis model, particle evacuation was 14, 18, 31, and 61 for UAS positions A, B, C, and D, respectively. Position D represents the alignment of the UAS tip flush with the f-URS tip. Stones were deposited in the lower calyx by gravity. Contour plots and vector displays showed the highest irrigation velocity in the UAS and f-URS channels, with a relative low-flow region between the UAS and f-URS tips. When the UAS and f-URS tips were aligned, this low-flow region substantially disappeared. Ureteral access sheath positioning significantly correlates with stone clearance rates. Maximal stone particle evacuation occurred when the distal tips of the UAS and f-URS were aligned. Variations in UAS position resulted in changes in local irrigation velocity.