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Extracorporeal Shock Wave Lithotripsy (ESWL) is a non-invasive medical procedure designed to help eliminate renal and biliary calculi, otherwise known as kidney stones and gallbladder stones, respectively. The procedure is generally painless and usually conducted on an outpatient basis without the need for anesthesia. However, ESWL patients are often given a sedative, most likely due to the simple fact that the procedure can take up to an hour to complete and the recipient must lie reasonably still. In some cases, the patient is kept occupied by being permitted to watch the entire process on an ultrasound monitor.
ESWL is accomplished through the use of a lithotriptor, a device that emits electrical impulses (shockwaves) initiated via an electrohydraulic, piezoelectric, or electromagnetic generator. The first lithotriptor introduced in the U.S. was the electrohydraulic Dornier HM3 in the early 1980s, which was originally designed to test components of supersonic aircraft. Its design is still considered to be the most reliable in terms of achieving optimum results. The latest generation of lithotriptors utilize an electromagnetic generator, which delivers high intensity impulses comparable to its predecessor, but with a much narrower focus.
During ESWL treatment, the patient reclines on the machine bed, which has a water-filled back support positioned behind the kidneys. Using x-ray or ultrasound imaging, the technician pinpoints the location of the stone or stones. Once targeted, a series of low-grade impulses are generated followed by intermittent periods of rest to allow the patient to become acclimated to the shockwave sensations, which are sometimes described as being snapped with a taut rubber band. However, these sensations may feel more intense if the stone is located near a bone, such as a rib. Slowly, shockwave levels are increased to a high frequency and a rate of up to 120 impulses per minute.
This treatment does not destroy the stone. However, the stone will be affected by shear stress, which will force it to break into small pieces. While this event signals the end of ESWL treatment, it is not the end of therapy for the patient. Within several days or weeks, small stone fragments are expected to pass through the urinary tract. To help facilitate this process and minimize discomfort, a ureteral stent is sometimes put into place to allow for easier transit and passage through the ureter.
Not every kidney or gallbladder stone patient is a candidate for ESWL. For one thing, it can’t be used if the patient is pregnant, has a pacemaker, or has kidney cancer. It should also be noted that this treatment is usually ineffective against kidney stones related to a genetic disorder characterized by excessive levels of the amino acid, cystine.