Effect of targeting and generator type on efficacy of extracorporeal shock wave lithotripsy

Analysis of the effect of technical factors, i.e. the type of stone targeting and shock wave generator, on ESWL efficacy. Evaluation of secondary outcomes to determine an optimal strategy for performing the procedure.

In the period from 01/2016 to 07/2021, we analyzed data from patients indicated for ESWL for nephrolithiasis and proximal or distal ureterolithiasis. This was a tricenter retrospective study to evaluate stone-free rates (SFR) while taking into account the number of ESWL sessions in four selected groups of patients with comparable characteristics. A patient is considered stone-free in the absence of residual lithiasis or with an asymptomatic residue of up to 2 mm. The real-time ultrasound-guided (USG) arm consisted of a group of 120 patients on the electromagnetic STORZ SLK lithotripter in the period from 02/2017 to 02/2020. A total of three comparison arms with x-ray guidance were created: A: 68 patients between 01/2016 and 03/2017 on the Medilit 7 electrohydraulic lithotripter. B: 72 patients from 04/2017 to 10/2017 on the Sonolith i-sys electroconductive lithotripter (EDAP). C: 120 patients from 03/2018 to 07/2021 on the STORZ SLK electromagnetic lithotripter. By comparing the US and x-ray guidance using the STORZ SLK lithotripter, the effect of targeting when using an identical device (electromagnetic generator) was evaluated. By comparing the arms A, B, and C, the efficacy in different types of generators - electromagnetic, electroconductive, electrohydraulic - was assessed when the same type of targeting (fluoroscopy) was used. The secondary parameters that were monitored included: the rate of use of auxiliary techniques in stone management; radiation exposure for the patient and/or operator; analgesic consumption; and the time required to perform the procedure.

When US versus x-ray guidance was compared in an electromagnetic lithotripter, SFRs of 90% vs. 85% (P=0.329), i.e. statistically comparable results, were obtained. By comparing electromagnetic, electroconductive, and electrohydraulic generators with fluoroscopy, SFRs of 85%, 88.9%, and 88.2% were obtained, respectively (P=0.727). When the degree of need for intraoperative analgesic administration was assessed, the electromagnetic generator was found to have a significantly lower consumption (20.8% vs. 30.6% vs. 48.5%) (P=0.0005). Values less than 1095 HU and 108.5 mm were shown to be optimal cut-off values for stone density and skin-to-stone distance, respectively.

Based on our comparative analysis, the noninferiority of US stone targeting was demonstrated compared to fluoroscopic targeting. No significant differences in ESWL efficacy were found using electrohydraulic, electroconductive or electromagnetic shock wave generators. With the electromagnetic lithotripter, there was a significantly lower analgesic consumption than with the electrohydraulic type.