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Extracorporeal shock wave lithotripsy

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A lithotriptor is a medical device used in the non-invasive treatment of kidney stones (urinary calculosis) and biliary calculi (stones in the gallbladder or in the liver). The scientific name of this procedure is Extracorporeal Shock Wave Lithotripsy (ESWL). Lithotripsy was developed in the early 1980s, and came into widespread use with the introduction of the HM-3 lithotriptor in 1983. Within a few short years, ESWL revolutionized treatment of calculosis. It is estimated that more than one million patients are treated annually with ESWL in the USA alone.

How it works

Lithotripsy attempts to break up the stones with minimal collateral damage by using an externally-applied, focused high-intensity acoustic pulse. The sedated or anesthesized patient lies down in the apparatus' bed, with his back supported by a water-filled coupling device placed at the level of kidneys, for instance. A fluoroscopic x-ray imaging system or an ultrasound imaging system are used to locate the stone and aim the treatment head such that the F1 of the shock wave is focused upon the offending stone. The treatment usually starts at the equipment's lowest power level, with a long gap between pulses, in order to accustom the patient to the sensation. The frequency of pulses & power level will then be gradually increased, in order to break up the stone more effectively. The final power level will usually depend on the patient's pain threshold. If the stone is positioned near a bone (usually a rib in the case of kidney stones), then this treatment may be more uncomfortable as the shock waves can cause a mild resonance in the bone which can be felt by the patient.

The successive shock wave pressure pulses result in direct shearing forces, as well as cavitation bubbles surrounding the stone, which fragment the stones in smaller pieces, which then can pass easily through the ureters or the cystic duct. The process takes about an hour. A ureteral stent (a kind of expandable hollow tube) may be used at the discretion of the urologist. The stent allows for easier passage of the stone by relieving obstruction, and through passive dilatation of the ureter.

Extracorporeal lithotropsy works best with stones between 4 mm and 2 cm in diameter, that are still located in the kidney. It can be used to break up stones which are located in a ureter, too, but with less success.

The patient undergoing this procedure can, in some cases, see for themselves the progress of their treatment. If allowed to view the ultrasound or x-ray monitor, they may be able to see their stone change from a distinct bright point, to a fuzzy cloud, as the stone is disintegrated into a fine powder.

ESWL is the least invasive of the commonplace modalities for definitive stone treatment, but provides a lower stone-free rate than other more invasive treatment methods, such as ureteroscopic manipulation with laser lithotripsy or percutaneous nephrolithotomy (PCNL). The passage of stone fragments may take a few days or a week and may cause mild pain. In order to dislodge fragments of the stone and carry them out of the kidney, patients may be subjected to repeated vigorous blows to the kidney while in a head-downward position for a week after the procedure, as well as instructed to drink as much water as is practical.

ESWL is not without risks. The shock waves themselves, as well as cavitation bubbles formed by the agitation of the urine medium can lead to capillary damage, renal parenchymal or subcapsular hemorrhage. This can lead to long-term consequences such as renal failure and hypertension. Overall complication rates of ESWL range from 5-20%.

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