Determinants of outflow rate during flexible ureteroscopy: an experimental in vivo study in an anesthetized porcine model

Purpose: 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). Material and Methods: This study was performed in an anesthetized porcine model. The fURS setup included a manual pumping system, a 9.5Fr single used-digital flexible ureteroscope and a ureteral access sheath (UAS). Outflow was collected and measured from the UAS during 1 minute in all experimental settings. The evaluated variables were the position of the ureteroscope, the pumping frequency (2s, 3s or 5s), the diameter of the used UAS (12/14Fr or 14/16Fr) and laser fiber (200 μm or a 272 μm). Results: Ureteroscope position in the lower calyx was associated with significantly lower outflow rate (p<0.05). The use of the 14/16Fr 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 14/16Fr UAS was being used.Pumping frequency did not show a significant correlation with outflow rate. Conclusions: The ureteroscope positioning and UAS size were important determinants of outflow rate 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.