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Extracorporeal shock wave lithotripsy for the treatment of renal stones. Treatment policy is as important for success as type of lithotriptor and patient selection.

OBJECTIVE
To compare the efficiency of different machines for extracorporeal shock wave lithotripsy (ESWL) of renal stones and to analyze treatment strategies and stone characteristics as determinants of treatment failure.


DESIGN
Prospective cohort study.


SETTING
Nationwide study in Sweden. All 11 hospitals in Sweden using 1 of 7 lithotriptors in 1991 were included.


PATIENTS
The study cohort comprised 1171 (97.6%) of the 1200 patients in Sweden who underwent ESWL for the first time because of renal stones between February 18, 1991, and December 31, 1991.


MAIN OUTCOME MEASURE
Treatment failure, defined as 1 or more residual renal stone fragments larger than 4 mm 1 of 3 months after the end of treatment, was analyzed after ESWL monotherapy and after ESWL plus auxiliary treatment using a multivariate analysis.


RESULTS
Treatment failure varied by center from 12% to 48% (mean, 24%) after ESWL monotherapy and from 4% to 40% (mean, 18%) after ESWL plus auxiliary procedures. After adjusting for differences in the patient mix, the risk of treatment failure, measured as the odds ratio, varied by center almost 7-fold after ESWL monotherapy and 20-fold after ESWL plus auxiliary treatment. Substantial differences also existed for the same equipment used at different centers. The risk of treatment failure increased rapidly for renal stones larger than 15 mm, and it was at least 2-fold higher in patients who had multiple stones or a cavity.


CONCLUSIONS
When ESWL is used for the treatment of renal stones, the treatment policy has as great an effect on the success rate and need for auxiliary treatment as optimal equipment and proper patient selection. Meaningful comparisons of different lithotriptors require multivariate analyses with adjustment for patient selection.