The New Lithotripsy Index predicts success of shock wave lithotripsy

The aim of this study is to evaluate the factors affecting treatment success in patients who underwent Shock wave lithotripsy (SWL) and to investigate the effect of the Storz Medical Lithotripsy Index (SMLI) on treatment effectiveness.

Prospective data were collected on patients undergoing SWL treatment for kidney stones between January 2013 and May 2021. Stone location, number and size were determined with non-contrast CT (NCCT) for all patients. All patients underwent SWL with a Storz Modulith SLK lithotripsy machine without anaesthesia. The total amount of energy applied to the stone was calculated using the SMLI. All patients were evaluated for stone-free status by X-ray at least 2 weeks after treatment. The success of the procedure was defined as the patient being completely stone free or the detection of residual fragments < 4 mm that did not require further treatment.

A total of 1230 patients with kidney stones were included in the study. The mean age of the patients was 42.33 ± 11.78 (18-75), and the mean BMI was 28.47 ± 8.78 (19.25-38.52). During SWL, 75.6% of patients demonstrated excellent pain tolerance (930/1230). A total of 116 patients could not tolerate the pain during SWL (9.4%). Treatment success was associated with fewer treatment sessions (2.34 ± 1.75 vs. 2.90 ± 2.04; p < 0.001), smaller stone size (7.52 ± 3.29 vs 8.60 ± 3.93; p < 0.001) and higher SMLI/stone size (25.11 ± 13.63 vs. 22.27 ± 14.50; p < 0.001). In the univariate and multivariate regression analysis, the factors affecting the success of the treatment were the number of sessions (OR 1.170), stone size (OR 1.142), number of shocks (OR 1.005), SMLI/stone size (OR 1.024) and pain tolerance (OR 0.692).

In the treatment of kidney stones with SWL, stone site, stone size, SMLI/stone size, and pain tolerance are the factors affecting success. SMLI per stone size is a statistically significant factor for predicting SWL success.