Shock wave lithotripsy: Gradual approach fails to improve stone outcomes

March 1, 2011

In vitro evidence suggests that increasing the energy level more slowly could not only improve fragmentation but also minimize renal injury. But a controlled, randomized trial didn't corroborate that evidence.

Key Points

That's what preliminary evidence suggested, and the concept finally was tested in a controlled, randomized blinded trial by urologists at St. Michael's Hospital, University of Toronto. But the study didn't corroborate that evidence, said senior author Kenneth T. Pace, MD, MSc. In fact, the gradual and high-power approaches ran neck and neck.

"Everybody knows SWL has revolutionized the treatment of kidney stones. However, effectiveness is not perfect, and other treatment modalities are gaining ground," said Dr. Pace, associate professor of urology at St. Michael's Hospital, University of Toronto. That's what has motivated the search for improved techniques.

Moreover, some preliminary evidence indicated that "priming" the kidney with fewer-than-usual or a relatively small number of low-energy shocks could minimize renal injury. Priming is theorized to promote vasoconstriction and thus prevent hemorrhage during lithotripsy.

Dr. Pace and his colleagues randomized nearly 200 patients to treatment with immediate (99) and gradual (96) SWL. All the patients presented with previously untreated, radiopaque single renal calculi.

In the immediate arm of the trial, patients underwent immediate voltage escalation for 3,000 shocks. Patients in the second arm also received about 3,000 shocks, but the voltage was escalated gradually from 15 kV for the first 900 shocks, 19 kV for the next 900, and the balance at the peak 23 kV.

Urologists blind to treatments assessed the outcomes on kidney-ureter-bladder radiographs taken 2 weeks and 3 months after treatment. Stone-free status was confirmed with non-contrast spiral computed tomography. The primary outcome was the success rate, defined as stone-free or adequate fragmentation ("sand" or asymptomatic fragments smaller than 4 mm) at 3 months. The team also measured biomarkers of renal injury: beta-2-microglobulin, a marker of proximal tubule injury, and microalbumin, a marker of glomerular injury. The clinical significance of these markers is not well established, but the team used them because they had the potential to be more sensitive than imaging at detecting renal injury, explained Dr. Pace, who presented the data at the 2010 AUA annual meeting in San Francisco.

No difference in success rates

There was no significant difference in success rates between the arms. Rates for those who underwent immediate treatment were 58% at 2 weeks and 57% at 3 months. In those who received gradual treatment, success rates were 65% at 2 weeks and 66% at 3 months. Ultrasound revealed no perinephric hematomas in either arm.

Levels of the markers at 1 hour, 1 day, and 7 days after treatment showed no significant differences. Moreover, complication rates, retreatment rates, and number of auxiliary procedures performed (eg, ureteroscopy) were similar between the two groups.

"While it's possible that there is some difference in voltage escalation strategy that may improve shock wave lithotripsy outcomes, it remains to be proved in any randomized trial," Dr. Pace concluded.