Alexander CE. et al., 2019: Impact of Case Volume on Shock Wave Lithotripsy Outcomes: Data from the National Shock Wave Lithotripsy Database of New Zealand
Alexander CE, Gowland S, Cadwallader J, Hopkins D, Reynard JM, Turney BW.
School of Medicine, University of St Andrews, St Andrews, United Kingdom.
Mobile Medical Technology, Christchurch, New Zealand.
Mobile Medical Technology, Auckland, New Zealand.
Oxford Stone Group, Department of Urology, Nuffield Department of Surgical Sciences, The Churchill Hospital, Oxford, United Kingdom.
Purpose: To assess the impact of individual operator case volume on shock wave lithotripsy (SWL) treatment outcomes in more than 9000 stone cases over a 20-year period in New Zealand. Materials and Methods: Stone cases treated with SWL on the Mobile Medical Technology (MMT) vehicle between June 19, 1995, and December 1, 2014, were identified. Data collection was undertaken prospectively for patient, stone, and treatment characteristics, and retrospectively for treatment outcomes. Multivariate analysis using binary logistic regression was undertaken to assess whether radiographer stone case volume (stones/year) was an independent predictor of SWL success (stone free or clinically insignificant residual fragments ≤4 mm at follow-up). Results: Sixteen radiographers delivered treatment to the included cohort (9039 stone cases), with a median case volume (stones/year) of 73 (range: 37-197) and median total of 425 stones treated (range: 71-1721). The two radiographers with highest case volumes achieved the highest success rates. Radiographer case volume (stones/year) was independently associated with SWL success (odds ratio [OR]: 1.004, 95% confidence interval [CI]: 1.003-1.005, p < 0.0001) and reduced need for post-SWL hospital admission (OR: 0.997, 95% CI: 0.994-1.000, p = 0.028), but there was no associated decrease in post-SWL urosepsis (OR: 0.999, 95% CI: 0.974-1.025, p = 0.941), perinephric hematoma (OR: 1.003, 95% CI: 0.985-1.020, p = 0.778), or need for auxiliary procedures (OR: 1.000, 95% CI: 0.998-1.002, p = 0.871). Conclusions: SWL success rates can be improved by increasing the frequency of cases performed by individual operators. In this multicenter cohort of more than 9000 stone cases treated over a 20-year period, the best outcomes were seen for those radiographers performing >150 cases per year.
J Endourol. 2019 May 9. doi: 10.1089/end.2019.0122. [Epub ahead of print]
It is difficult to comment this statistic based paper.
First and single treatment stone cases over a 20-year study period were evaluated. This is a very long time period of possible changes.
Successful ESWL was defined as no or/and residuals or fragments 4 mm. “The overall treatment success rate was 49.2% (35.9% stone free, 13.3% CIRFS), with 6.7% (n = 627) of cases requiring post-SWL hospital admission and 9.5% (n = 891) requiring post-SWL auxiliary procedures” It is not stated if or how many secondary ESWL’s were done. Very probably none in the cases evaluated.
Multivariate analysis slightly confirmed the expected correlation: the results improved with the case numbers done per year. But case volume alone was not correlated to success.
In fact case volume alone showed no correlation to the success rate ( Fig.1).
Fig.1 Total volume of single radiographers versus success rate of single radiographer. Adapted from the present paper
The authors stated “It may be the case that those operators who performed SWL with the greatest frequency were also able to create a more effective collective team performance, working with the anesthetist, urologist, and nursing staff, to deliver improved SWL outcomes.” But then not volume but other factors are dominant. These are the typical causal speculations on difficult to interpret statistical results. It is well known from open surgery that some surgeons are gifted and some or not. So neither the case volume nor the cases per year may be the right indicator.