Progressive increase of lithotripter output produces better in-vivo stone comminution.

BACKGROUND AND PURPOSE Shockwave lithotripsy (SWL) has become a first-line intervention for treatment of nephrolithiasis. However, few studies have examined the effects of modifications in the method of shockwave energy administration on comminution efficiency. We propose that a gradual increase in output voltage will produce superior stone fragmentation in comparison with a constant or a decreasing output voltage by optimizing the stress wave and cavitation erosion forces on renal calculi. MATERIALS AND METHODS BegoStone phantoms were implanted in the renal pelvis of 11 pigs that underwent SWL at a pulse repetition rate of 1 Hz. Animals in the increasing strategy group (N = 4) were subjected to 18, 20, and 22 kV for 600, 600, and 800 shocks, respectively. The second group (N = 4) received a decreasing strategy of 22, 20, and 18 kV for 800, 600, and 600 shocks, respectively. The third group (N = 3) received all 2000 shocks at 20 kV, mimicking the clinical protocol. RESULTS A progressively decreasing strategy and constant output voltage produced a mean comminution efficiency, or percentage of stone fragments <2 mm, of 89.0% +/- 3.3% and 87.6% +/- 1.7%, respectively. The mean comminution efficiency was improved to 96.5% +/- 1.4% by using the increasing strategy (P = 0.01). CONCLUSIONS A progressive increase in lithotripter output voltage during SWL can produce greater stone fragmentation than protocols employing constant or decreasing output voltage.