Determinants of outflow rate through the ureteral access sheath during flexible ureteroscopy: an experimental in vivo study in an anesthetized porcine model.

To evaluate the effect of different ureteroscope positions, saline pumping frequency, laser fiber diameter and ureteral access sheath (UAS) on outflow rate during flexible ureteroscopy (fURS). This study was performed in an anesthetized porcine model. The fURS setup included a manual pumping system, a 9.5 Fr single used-digital flexible ureteroscope and a ureteral access sheath (UAS). Outflow was collected and measured from the UAS during 1 min in all experimental settings. The evaluated variables were the position of the ureteroscope, the pumping frequency (2 s, 3 s or 5 s), the diameter of the used UAS (12/14 Fr or 14/16 Fr) and laser fiber (200 μm or a 272 μm). Ureteroscope position in the lower calyx was associated with significantly lower outflow rate (p < 0.05). The use of the 14/16 Fr UAS resulted in improved flow in the renal pelvis and upper calyx (p < 0.05) but not in the lower calyx. The use of a 200 μm laser fiber only improved flow in the upper calyx and when a 14/16 Fr UAS was being used. Pumping frequency did not show a significant correlation with outflow rate. The ureteroscope positioning and UAS size were important determinants of outflow rate through the UAS during fURS, while laser fiber diameter had a limited effect. In the lower calyx the outflow was minimal and was not improved by using a larger UAS.