Concurrent stone stabilization improves ultrasonic and pneumatic efficacy during cystolithopaxy: an in vitro analysis

OBJECTIVE: To identify whether stabilization of larger bladder stones would improve the efficacy of combination (ultrasonic/pneumatic) lithotripsy in a phantom bladder stone model for percutaneous cystolithopaxy. MATERIALS AND METHODS: Using 1cm phantom Bego stones, a spherical model bladder was used to simulate percutaneous bladder access. A UroNet (US Endoscopy, USA) was placed alongside a Swiss Lithoclast probe through the working channel of a Storz 26Fr rigid nephroscope. Using a 30Fr working sheath, the stone was captured, and fragmented for 60seconds. Resulting fragments and irrigation were filtered through a 1mm strainer, and recorded. Five trials were performed with and without the UN. Durability was then assessed by measuring net defects, and residual grasp strength of each instrument. Descriptive statistics (mean, standard deviations) were used to summarize the data, and Student’s t-tests (alpha<0.05) were used to compare trials. RESULTS: The mean time to stone capture was 12s (8-45s). After fragmentation with UN stabilization, there were significant improvements in the amount of residual stone (22% dry weight reduction vs 8.1% without UN, p<0.001), number of fragments (17.5 vs 5.0 frag/stone, p=0.0029), and fragment size (3.6mm vs. 7.05 mm, p=0.035). Mesh defects were noted in all nets, ranging from 2-14 mm, though all but one net retained their original grip strength (36.8N). CONCLUSIONS: Bladder stone stabilization improved fragmentation when used in conjunction with ultrasonic/pneumatic lithotripsy. However, due to limitations in maneuverability and durability of the UN, other tools need to identified for this indication.