MP63-10 IMPACT OF URETERAL ACCESS SHEATH DIAMETER ON THE OUTCOMES OF FLEXIBLE URETEROSCOPIC STONE REMOVAL AS DETERMINED BY THE URETEROSCOPIC STONE EFFICIENCY QUOTIENT

Abstract

INTRODUCTION AND OBJECTIVE: The use of a ureteral access sheath (UAS) during flexible ureteroscopy (URS) enhances pressure-flow dynamics within the collecting system, resulting in improved visualization and maintenance of lower intrarenal pressure. As the diameter of the deployed UAS increases, there is a concomitant improvement in irrigant flow and easier removal of larger stone fragments. We evaluated the impact of the largest diameter UAS (i.e. 16 Fr), on post URS computed tomography (CT) stone free rates (SFR) and herein introduce the concept of the ureteroscopic stone efficiency quotient (USEQ). METHODS: We reviewed our prospectively maintained database, and evaluated patients undergoing URS for renal calculi with the use of an 11 Fr, 14 Fr, or 16 Fr UAS. At the outset of each case, passage of a 16 Fr UAS was attempted; if the 16 Fr UAS did not pass easily, then the UAS was downsized to a smaller sheath. Patient demographics, stone parameters, procedure time, and postoperative CT scan results were recorded. SFR was defined as complete absence of stones. The USEQ was defined as: %SFR / operative time (minutes) X 100. We evaluated the outcomes of the three UASs using student’s T test, Chi square test, and logistic regression. RESULTS: Among 110 patients undergoing URS between January 2018 and June 2019, 56 patients with renal stones (65 renal units) had a postoperative CT. Mean aggregate stone size was 15±7 mm, number of stones 2.7±1.6, and stone density 711±430 HU. We deployed 11 Fr, 14 Fr, and 16 Fr UAS in 12%, 29%, and 59% of renal units, respectively. Stone parameters did not differ significantly among the three groups. Median time to patients’ postoperative CT was 39 days. The overall SFR was 55%. Using univariate analysis, the stone-free cohort had smaller aggregate stone size (13 vs. 18 mm, p=0.03) and fewer stones (2.2 vs. 3.2, p=0.01). The SFR for 16 Fr vs. 14 Fr was 58% and 63% (p=0.7) while the SFR for 16 Fr vs. 11 Fr was 58% and 25% (p=0.09). There were 3 (4.6%) UAS-induced high grade ureteral injuries noted as a split in the urothelium (post ureteroscopy lesion scale = 3, based on a 0-5 scoring system); all were treated with a ureteral stent. The use of 16 Fr UAS was associated with shorter operative time (92 minutes) compared to the 14 Fr UAS (139 minutes, p=0.03) and 11 Fr UAS (118 minutes, p=0.53). The USEQ was markedly improved with use of the 16 Fr UAS: 64 vs. 14 Fr: 45 vs. 11 Fr: 21. CONCLUSIONS: Use of a 16 Fr UAS vs. a 14 Fr or 11 Fr UAS reduced operative time without impairment of SFR while markedly augmenting the ureteroscopy stone efficiency quotient. Source of Funding: none