TREATMENT OF URINARY CALCULI IN A PORCINE AND CANINE MODEL USING THE BROWNE-PNEUMATIC-IMPACTOR

Objectives. To define the safety and efficacy of a pneumatically driven, mechanical lithotriptor using nitinol probes through semirigid and actively deflectable, flexible fiberoptic endoscopes. Methods. The Browne Pneumatic Impactor (BPI) uses standard compressed air to drive a nitinol wire along its long axis onto a calculus, fragmenting it. Bench top and in vivo experiments were designed to explore variables, including the effects of various nitinol probe tip designs, outer diameters, excursion distances, and sheathing materials as well as the efficiency of fragmentation with active endoscope deflection. In vivo experiments in two animal models (porcine and canine) were performed using small diameter, fiberoptic semirigid, and actively deflectable, flexible ureteroscopes. Surgically placed calculi were fragmented with the BPI and representative tissue was obtained immediately and up to 2 weeks postoperatively to define histologic changes. A panel of human urinary calculi was chosen for their relative difficulty in fragmentation with other modalities. Results. Calculi, including pure calcium oxalate monohydrate, brushite, cystine, and triamterene, were fragmented with the BPI used through both semirigid and actively deflectable, flexible endoscopes. A rounded tip design and excursions of 1 mm fragmented calculi most efficiently with minimal histologic reaction. Retrograde stone migration before fragmentation was noted in dilated upper urinary tracts. This was prevented by first entrapping the calculus within a standard basket. Ureteral calculi were fragmented with the nitinol probes deflected up to 45 degrees by the flexible endoscope. With increased active deflection, the efficiency of fragmentation decreased. Conclusions. The BPI represents a safe, thermal-free endoscopic lithotrite able to fragment the hardest calculi through semirigid and flexible ureteroscopes.