Lithotriptor

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Steven C. Campbell, M.D., Ph.D.


Overview

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 in Germany by Dornier Medizintechnik GmbH (now known as Dornier MedTech Systems GmbH), 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 stone 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 is used to locate the stone and aim the treatment head so that the F1 of the shock wave is focused on the 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 and the 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), this treatment may be more uncomfortable because the shock waves can cause a mild resonance in the bone which can be felt by the patient. The sensation of the treatment is likened to an elastic band twanging off the skin, and the patient is shocked in time with his heartbeat (he will be hooked up to an ECG).

The successive shock wave pressure pulses result in direct shearing forces, as well as cavitation bubbles surrounding the stone, which fragment the stones into smaller pieces that 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 patients 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 stones 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. Patients may be instructed to drink as much water as is practical during this time.

A patient of the procedure has equated the the after effects to "a punch to the kidney". (pain while urinating, with blood evident)

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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