Extra Corporeal Shock Wave Therapy

What Is Extra Corporeal Shock Wave Therapy?

Extracorporeal shock wave lithotripsy (ESWL) involves the use of a lithotriptor machine to deliver externally-applied, focused, high-intensity pulses of ultrasonic energy to cause fragmentation of a stone over a period of around 30–60 minutes.

Following its introduction in United States in February 1984, ESWL was rapidly and widely accepted as a treatment alternative for renal and ureteral stones. ESWL is currently used in the treatment of uncomplicated stones located in the kidney and upper ureter, provided the aggregate stone burden (stone size and number) is less than 20 millimeters (0.79 in) and the anatomy of the involved kidney is normal.

In fact, some 80 – 85% of simple renal calculi can be effectively treated with shock wave lithotripsy. A number of factors can influence the efficacy of ESWL, including chemical composition of the stone, presence of anomalous renal anatomy and the specific location of the stone within the kidney, presence of hydronephrosis, body mass index, and distance of the stone from the surface of the skin.

Common adverse effects of ESWL include acute trauma such as bruising at the site of shock administration and damage to blood vessels of the kidney. In fact, the vast majority of people who are treated with a typical dose of shock waves using currently accepted treatment settings are likely to experience some degree of acute kidney injury. ESWL-induced acute kidney injury is dose-dependent (increases with the total number of shock waves administered and with the power setting of the lithotriptor) and can be severe including internal bleeding and subcapsular hematomas.

On rare occasions, such cases may require blood transfusion and even lead to acute renal failure. Hematoma rates may be related to the type of lithotriptor used; hematoma rates of less than 1% and up to 13% have been reported for different lithotriptor machines. Recent studies show reduced acute tissue injury when the treatment protocol includes a brief pause following the initiation of treatment, and both improved stone breakage and a reduction in injury when ESWL is carried out at slow shock wave rate.

In addition to the aforementioned potential for acute kidney injury, animal studies suggest that these acute injuries may progress to scar formation, resulting in loss of functional renal volume. Recent prospective studies also indicate that elderly people are at increased risk of developing new-onset hypertension following ESWL. In addition, a retrospective case-control study published by researchers from the Mayo Clinic in 2006 has found an increased risk of developing diabetes mellitus and hypertension in people who had undergone ESWL, compared with age and gender-matched people who had undergone non-surgical treatment.

Whether or not acute trauma progresses to long-term effects probably depends on multiple factors that include the shock wave dose (i.e., the number of shock waves delivered, rate of delivery, power setting, acoustic characteristics of the particular lithotriptor, and frequency of retreatment) as well as certain intrinsic predisposing pathophysiologic risk factors.

To address these concerns, the American Urological Association established the Shock Wave Lithotripsy Task Force in order to provide expert opinion on the safety and risk-benefit ratio of ESWL. The task force published a white paper outlining their conclusions in 2009. The task force concluded that the risk-benefit ratio remains favorable for many people. The advantages of ESWL include its noninvasive nature, the fact that it is technically easy to treat most upper urinary tract calculi, and that, at least acutely, it is a well-tolerated, low-morbidity treatment for the vast majority of people. However, they recommended slowing the shock wave firing rate from 120 pulses per minute to 60 pulses per minute to reduce the risk of renal injury and increases the degree of stone fragmentation.

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