ASA/CAA '05 Meeting, Vancouver, BC

Improving Shock Wave Lithotripsy Results
by Modifying Treatment Rate and Voltage Escalation

Kenneth Pace kenneth.pace@utoronto.ca
St. Michaels Hospital, University of Toronto
Toronto, ON M5C 2T2

In collaboration with R. John Honey and the University of Toronto Lithotripsy Research Group.

Popular version of paper 1aBB7
Presented Monday Morning, May 16, 2005
ASA/CAA '05 Meeting, Vancouver, BC

Shock wave lithotripsy (SWL) has revolutionized the treatment of kidney stones over the last two decades. Nevertheless, SWL is not always effective and does have a low risk of complications. As a result, other minimally-invasive treatments for kidney stones, such as treatments with small incisions (percutaneous nephrolithotomy) or small telescopes (ureteroscopy) have been gaining ground.

Laboratory experiments have suggested that there are ways to improve the effectiveness of SWL and minimize tissue damage caused by the treatment that might prove useful in treating patients. These include slowing down the frequency at which shock waves are administered during treatment, and possibly changing the way that the energy level of treatment is increased during treatment.

Originally, SWL was performed at the same speed as the patients heart rate (generally 60 to 80 shocks per minute) because of concerns that the shock waves might cause heart rhythm irregularities. However, it soon because apparent that the SWL treatment speed could be safely increased without effecting the heart, and so most centres world-wide now treat at a speed of 120 shocks per minute, which allows for shorter treatment times. This increase in treatment speed was not studied closely at the time. Looking back, it is obvious that the treatment outcomes of faster SWL machines were inferior to the original results at slower rates. Most felt that these differences were due to design differences in the more modern second- and third-generation lithotripters, but we feel that at least part of this difference is due to the faster SWL treatment rate currently used.

Based on animal and laboratory data, we have carried out two clinical trials comparing SWL treatments performed at 60 and 120 shocks per minute, for stones located in the kidney and for stones located in the ureter. We found in both cases that treatment at the slower rate of 60 shocks per minute was more effective: fewer shocks were needed to fragment the stone, and successful stone fragmentation was more likely at the slower treatment rate. This had the added benefit of decreasing the likelihood patients would need a second SWL treatment for their stone, and also decreased their chances of complications such as emergency room visits for pain from fragment passage. The advantage of the slower treatment rate of 60 shocks per minute is particularly dramatic for larger stones. One disadvantage of slowing the treatment rate is that each treatment takes an average of 16 minutes longer to perform.

We are currently exploring other possible ways to improve SWL effectiveness by changing the way that the energy level of the shock wave is increased during treatment. These new methods are being evaluated with clinical trials that will likely conclude in the next 18 months.