Shock wave lithotripsy: advances in technology and technique

Shock wave lithotripsy (SWL) represents the only noninvasive surgical treatment for urinary tract stones. Drawing on their considerable experience, Lingeman and colleagues outline the current utility and limitations of SWL, and highlight the technological advances that hold promise for improving the safety and efficacy of this treatment modality in the future. Shock wave lithotripsy (SWL) is the only noninvasive method for stone removal. Once considered as a primary option for the treatment of virtually all stones, SWL is now recognized to have important limitations that restrict its use. In particular, the effectiveness of SWL is severely limited by stone burden, and treatment with shock waves carries the risk of acute injury with the potential for long-term adverse effects. Research aiming to characterize the renal response to shock waves and to determine the mechanisms of shock wave action in stone breakage and renal injury has begun to suggest new treatment strategies to improve success rates and safety. Urologists can achieve better outcomes by treating at slower shock wave rate using a step-wise protocol. The aim is to achieve stone comminution using as few shock waves and at as low a power level as possible. Important challenges remain, including the need to improve acoustic coupling, enhance stone targeting, better determine when stone breakage is complete, and minimize the occurrence of residual stone fragments. New technologies have begun to address many of these issues, and hold considerable promise for the future. Key Points Shock wave lithotripsy (SWL) is the only noninvasive surgical technique to remove urinary stones, and is the most common treatment for solitary, uncomplicated, small upper urinary tract calculi Some stone types can be highly resistant to shock waves; clinically relevant residual fragments are common in SWL, and re-treatment following SWL is common Shock wave treatment can rupture blood vessels, and acute renal injury can be severe; inflammation in the kidney following SWL can lead to scarring with permanent loss of functional renal mass Success rate in SWL is significantly increased by treating at a slow shock wave rate; renal injury is also reduced by treatment at slow shock wave rate, and by step-wise treatment employing a pause between steps Lithotripter focal width affects stone breakage, and a wide focal zone is an advantage Most urologists are likely to overtreat with shock waves because the breakage end point is hard