Abstract
The relationship between case volume and outcomes has been studied in a number of areas. Improved outcomes with higher volumes for both individuals and centers have been reported for a number of surgical procedures including percutaneous nephrolithotomy, ureteroscopy, and extracorporeal shockwave lithotripsy (SWL).
The authors are to be congratulated on this large study that involves >900 patients treated with SWL for >20 years. The data were collected prospectively for patients, stones, and treatment characteristics and analyzed retrospectively for treatment outcomes. A multivariable analysis was undertaken to assess whether the treating radiographer's stone case volume per year was an independent predictor of SWL success. Success was defined as stone-free or clinically insignificant residual fragments ≤4 mm in diameter on follow-up.
In this study, radiographers were the primary operators, supervised clinically by a urologist. Previous reports have demonstrated comparable efficacy and outcomes between experienced urologists and radiographer technicians. Sixteen radiographers had a median case volume of 73 stones treated per year. The two radiographers with the highest case volumes (132 and 171) achieved the highest success rates of 62.1% and 66.4%. There was, however, a wider variation of SWL success between radiographers, which ranged from 31.4% to 66.4%. The overall treatment success rate was 49.2%. Although this is lower than one would expect, multiple stones (30.6%) were included and the average stone size was large at 9.9 mm. The authors did not document the shock wave frequency used, but as data were collected as far back as 1995, the majority of cases must have been treated at a rate of 120 shocks per minute. The randomized trial by Pace et al. 1 reported a success of 74.5% at a rate of 60, but 60.6% at 120 shocks per minute. For stones 10 mm or larger, the difference was 71% and 32%.
The majority of cases were treated under general anesthesia (87.4%). This is similar to the rate in the United States (82.1%) that was demonstrated in a study by Lantz and coworkers 2 comparing practice patterns between American and Canadian urologists, which showed that only 5.3% of Canadian urologists used general anesthesia for SWL.
The authors acknowledge limitations to their study. In their analysis, they did not include obesity and stone density as these data were not collected. Also 17.1% of cases did not receive follow-up of their postprocedure imaging.