Appropriate cutoff for treatment of distal ureteral stones by single session in situ extracorporeal shock wave lithotripsy

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Objectives: To determine an appropriate cutoff for treatment by single session in situ extracorporeal shock wave lithotripsy for a prevesical stone by determining the differences in the efficiency quotient (EQ).Methods: This was a review of a series of patients who underwent shock wave lithotripsy for a primary, single, prevesical stone from January 1995 to June 2003. All 153 patients were treated using a Dornier MPL 9000 lithotripter in the prone position under intravenous sedation. The stone size was measured in two dimensions (parallel and perpendicular to the long axis of the ureter). The EQ was calculated using a standard formula.Results: Of the 153 patients, 141 (92.2%) were stone free within a mean period of 12.2 +/- 12.2 days (EQ 68.8). No significant complications occurred, and none of the patients required admission. The treatment failed in 10 patients (6.5%), who subsequently required an ancillary procedure (ureteroscopy). Statistically, we found 7 mm to be an appropriate cutoff for treatment using in situ shock wave lithotripsy. The EQ for stones greater than 7 mm and those 7 mm or smaller was 58 and 81, with a stone-free period of 13.6 +/- 12.9 and 10.9 +/- 11.6 days, respectively.CONCLUSIONS: Ultrasound-guided shock wave lithotripsy is an efficient and safe modality for the treatment of prevesical stones 7 mm or less. Using an echo-guided lithotripter, the treatment was a radiation-free, day care procedure performed under intravenous sedation. Only 11% of our patients required repeat treatment.