Efficacy of ultrasound monitoring during extracorporeal shock wave lithotripsy: A multi-institutional propensity score-matched study

Objectives To evaluate the efficacy of ultrasound-assisted monitoring during shock wave lithotripsy for kidney and proximal ureteral calculi. Methods We retrospectively reviewed 535 patients who initially underwent shock wave lithotripsy for renal or proximal ureteral calculi between January 2012 and December 2021. The patients were divided into the X-ray group (n = 294) and ultrasound plus X-ray group (n = 241) based on the methods of targeting and monitoring calculi during shock wave lithotripsy. Because of differences in patient backgrounds, 1:1 propensity score-based matching was performed. The primary endpoint was the stone-free rate. Results In the final 1:1 matched cohort, 192 kidney stone cases and 162 proximal ureteral stone cases were analyzed. For patients with kidney calculi, the stone-free rate of the ultrasound plus X-ray group was significantly higher than that of the X-ray group (66.7% vs. 47.9%; P = 0.013). In the multivariate analysis, a large stone area (odds ratio 2.37), lower caliceal stones (odds ratio 3.37), and X-ray monitoring alone (odds ratio 0.49) were independently associated with shock wave lithotripsy failure. For patients with proximal ureteral stones, there was no significant difference in the stone-free rate between the ultrasound plus X-ray group and X-ray group (71.6% and 58.0%, respectively; P = 0.100). During the multivariate analysis, high computed tomography attenuation (odds ratio 2.31) and large stone area (odds ratio 2.18) were independent factors associated with residual stones after shock wave lithotripsy. Conclusions Ultrasound-assisted monitoring may contribute to a higher stone-free rate for patients with kidney calculi, but not for those with proximal ureteral calculi.