Potential Benefits of Shock Wave Lithotripsy May Outweigh Risks

Laurie Barclay, MD

December 03, 2009

December 3, 2009 — For shock wave lithotripsy (SWL), potential benefits in treating renal stones outweigh the foreseeable risks, according to a white paper from the American Urological Association (AUA) posted online November 25. This consensus statement offers expert opinion concerning the safety of SWL, the significance of long-term adverse events, and the balance of benefits vs harms linked to this treatment.

"The field of SWL is continually advancing," task force member and coauthor Dean G. Assimos, MD, from Wake Forest University School of Medicine in Winston-Salem, North Carolina, said in a news release. "It is important for all practitioners to be aware of these new treatment protocols so that they can reduce the risk of renal injury for patients suffering from stones."

Since SWL was first introduced into the United States in 1984, it has been widely used for renal calculi, particularly when other treatments are not available, because it is noninvasive, effective for most upper urinary stones, and is well tolerated. However, retreatment may be necessary.

Indications for SWL include most uncomplicated upper urinary tract stones calculi with aggregate stone burden of less than 2 cm in patients with normal renal anatomy. Except during pregnancy, it is also a suitable therapy option for ureteral stones anywhere in the ureter and for mid and lower ureteral stones in women of childbearing age.

Risks of Using SWL

However, shock waves needed to break up stones may potentially cause tissue damage and acute injury, resulting in long-term adverse effects. Complications of SWL may include scar formation and long-term loss of functional renal tissue. Damage to renal veins may result in parenchymal bleeding and mild to severe subcapsular hematomas, with risk for hematomas doubling with each additional decade of patient age.

Although use of SWL has been associated with the development of diabetes mellitus and new-onset hypertension, some patients with renal calculi are already at greater risk for the development of diabetes mellitus and hypertension before being treated with SWL. Despite this controversy, the white paper warns clinicians to use extra caution in anticipating and managing these conditions in patients who have been treated with SWL. In addition, the long-term sequelae of acute SW injury merit further investigation.

Although there is a likely to be a treatment threshold at which SWL injury begins, the upper limit for SW dose that can be delivered without causing vascular trauma is still unknown. Some degree of acute renal trauma is likely in most patients treated with a typical dose of SWs using currently accepted treatment settings.

To date, it is also undetermined whether injury resulting from a single treatment session may cause lasting damage. Pertinent factors may include SW dose, determined by SW number, power, SW rate, and treatment sequence. In addition, specific pathophysiologic risk factors may make a particular patient and/or kidney more vulnerable to injury.

"The risk factors for acute SWL injury may not be the same as those for chronic effects," the white paper authors write. "Thus, the safety of SWL depends on multiple factors that include the dose, treatment settings and acoustic characteristics of the lithotripter used, frequency of retreatment, and a background of physiologic factors that may predispose the patient to increased risk of acute injury or progression to long-term damage. Recent studies with experimental animals demonstrating that renal injury is significantly reduced at slow SW rate or when a protective 'pretreatment' protocol is used are very encouraging, and suggest that under proper conditions lithotripsy can be both safe and effective."

Recommendations to Reduce Renal Injury

New protocols to lower the risk for renal injury from SWL are also presented. The white paper recommends a brief, 3- to 4-minute pause in shock wave delivery soon after SWL treatment is started, based on animal studies showing the protective effects of instituting such a pause, including decreased bleeding within renal tissue.

To reduce renal injuries and improve stone breakage outcomes, the white paper also recommends slowing the SW firing rate from the typical firing rate of 120 SW per minute to 60 SW per minute. Recent research suggests that the lower SW is associated with a decreased risk for renal injury. Despite the modest increase in overall treatment time needed for use of the lower firing rate, clinical evidence to date have shown better success rates for stone fragmentation and lower rates of renal injury.

The white paper notes the need for additional research to improve efficacy outcomes from SWL and to lower the rate of adverse events.

"Shock wave lithotripsy is often the best treatment option, in some settings may be the only treatment available and, in most cases, presents distinct advantages that outweigh the foreseeable risks," the white paper authors write. "Like any of the stone technologies there are risks in using SWs, but it is also true that new treatment strategies are being developed that reduce adverse effects and improve stone breakage outcomes."

"Steps that significantly reduce acute injury may have the potential to eliminate long-term adverse effects altogether," the study authors conclude. "Still, limited understanding of the factors that lead to lasting injury after SWL calls for continued research on the mechanisms and consequences of SW injury."

Some of the authors of the white paper have disclosed various financial or other relationships with Altus; American Medical Systems; Boston Scientific Corp; Lumenis; Med Review in Urology; Urology Times; California Urological Services; Astellas; Olympus; Siemens Medical Solutions; Beck Analytical Laboratories; Midstate Mobile Lithotripsy, LP; and/or Beck Analytical Laboratories.

American Urological Association (AUA) White Paper. Published online November 25, 2009.


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