Slow Shock Wave Lithotripsy Found Most Effective

A new study has found that regardless of the type of lithotripter used, slow shock wave lithotripsy (SWL) delivery at 60 shock waves per minute delivered the best results for pulverizing kidney stones.

Researchers at the Johns Hopkins University School of Medicine (Baltimore, MD, USA) performed a systematic review and meta-analysis of four trials comprising 589 patients to define the effect of shock wave rate on the outcome of SWL. Studies that compared SWL treatment at 60 shocks per minute to treatment at 120 shocks per minute were included in the analysis. The primary outcome measure was treatment outcome (success, failure), as defined by the authors of the source studies. The difference in the proportion of patients with a successful treatment outcome was compared between the 60 and 120 shocks per minute groups as a risk difference, and risk differences were pooled across the four trials with a fixed effects model.

The results showed that patients treated at a rate of 60 shocks per minute had a significantly greater likelihood of a successful treatment regardless of stone size, although one trial found that the benefits were more apparent among stones larger than one centimeter. The researchers theorized that the mechanism of action for the beneficial effect of the slower treatment delivery might relate to irregularities along the stone's surface that may blunt the negative pressure portion of the shock wave at the higher delivery level. The study was published in the January 2008 issue of the Journal of Urology.

"Our meta-analysis suggests that patients treated at a rate of 60 shocks per minute have a significantly greater likelihood of a successful treatment outcome than patients treated at a rate of 120 shocks per minute,” concluded lead author Michelle Semins, M.D.
Extracorporeal shock wave lithotripsy (ESWL) uses shock waves to break a kidney stone into small pieces that can more easily travel through the urinary tract and pass from the body. Lithotripsy attempts to break up the stone with minimal collateral damage by using an externally applied, focused, high-intensity acoustic pulse.

The successive shock wave pressure pulses result in direct shearing forces, as well as cavitation bubbles surrounding the stone, which fragment the stones into smaller pieces. The process takes about an hour. A ureteral stent may be used at the discretion of the urologist to allow for easier passage of the stone by relieving obstruction and through passive dilatation of the ureter.


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Johns Hopkins University School of Medicine