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ESWL: Technique and Complications of Extracorporeal Shock Wave Lithotripsy

Extracorporeal shock wave lithotripsy (ESWL) is a noninvasive technical procedure in urology that enables the disintegration of urinary stones by shock waves without anesthesia. ESWL was developed in Munich in 1981 (Chaussy et al., 2002 (Reprint)).

Indications for ESWL

Kidney stones less than 2 cm in diameter may be treated with ESWL. Ureteral stones in the proximal ureter are still also treatable. Locating and positioning the shock source for distal ureteral stones is more complex but possible (Bach u.a., 2011).

Contraindications to ESWL

Absolute contraindications to ESWL:

• Coagulation disorders
• Platelet aggregation inhibitors (e.g., ASS)
• Pregnancy
• Aortic aneurysm
• Untreated urinary tract infection
• Stone localization with imaging during ESWL not possible.

Relative contraindications to ESWL:

• Urinary tract obstruction. ESWL on small ureteral stones may be done even with urinary tract obstruction

Physical Principles of Extracorporeal Shock Wave Lithotripsy (ESWL)

Multifunctional table with extracorporeal shock wave lithotripsy (ESWL): imaging for stone localization is possible with fluoroscopy or ultrasonography.

The principle of ESWL is externally generated shock waves, which are directed into the patient's body and focused on the target (kidney or ureter stone). Three different generator types for shock wave lithotripsy exist:

Electromagnetic ESWL:

The shock wave is generated by an electromagnetic coil, which moves a membrane (like a loudspeaker). An acoustic lens system reflects and focuses the shock wave. Examples: Dornier Doli, Lithostar Siemens.

Electrohydraulic ESWL:

The shock wave is generated by an underwater spark discharge, which is reflected by an ellipsoid. Example: Dornier HM3.

Piezoelectric ESWL:

A piezoelectric crystal is mechanically deformed if electricity is applied. The crystals are aligned along a spherical dish, allowing the shock waves to focus. Example: PiezoLith of Wolff.

Surgical Technique of Extracorporeal Shock Wave Lithotripsy

Prerequisites for ESWL:

• Upper urinary tract obstruction should be treated by the placement of a ureteral stent (DJ). The insertion of a DJ should also be considered before treating a large kidney stone since the fragments may obstruct the ureter ("Steinstraße"). Small ureteral stones with moderate hydronephrosis may be treated without DJ since fragmentation may resolve the hydronephrosis.
• Coagulation and platelet function should be normal: PTT, PT, blood count.
• Normal blood pressure
• Sterile urine, perioperative antibiotic prophylaxis is not necessary.
• Patient has signed informed consent
• Stone can be located with the imaging system
• Bubble-free coupling of the shock source to the patient with ample gel.

Monitoring of the patient:

Monitoring of the oxygen saturation, ECG, and blood pressure during extracorporal shock wave lithotripsy is recommended.

Analgesia:

The better the analgesia, the higher the stone-free results after ESWL due to minimizing patient movements (pain, respiration). The minimum is a conscious sedation with, e.g., midazolam and piritramide.

Imaging for Stone Localization:

Imaging for stone localization can be done with ultrasound, fluoroscopy, or a combination of both. The localization must be checked regularly during treatment, as patients often move due to pain.

Dosage of Shock Waves:

2000–4000 shock waves are used with a 60–120/min frequency. Comparative studies found a higher efficacy of ESWL with a lower frequency of shock waves (60 vs. 120/min). Shock waves generate microscopic cavitation bubbles in the focus, which rapidly disintegrate spontaneously. With a high frequency of shock waves, the energy of the next shock wave is lost due to the cavitation bubbles of the former shock wave, leaving the kidney stone intact.

The power of the shock wave depends on the patient's pain threshold or is set according to the recommended maximum value by the manufacturer of the ESWL machine. A pause of several days should be in between treatment sessions.

Follow-up after ESWL

Imaging (ultrasound, KUB X-ray) is necessary to evaluate stone clearance, upper urinary tract obstruction or to detect renal hematoma. Upper urinary tract obstruction symptoms are treated with NSAID (e.g., Diclofenac 75 mg 1-0-1) and alpha blockers (e.g., tamsulosin 0,4 mg 1-0-0, off-label).

Partial disintegration after extracorporeal shock wave lithotripsy (ESWL): imaging before and after a treatment session of ESWL (3000 shock waves).

Complications after ESWL

Blood pressure:

Low blood pressure with nausea and vomiting is possible.

Bleeding:

Bleeding leads to hematuria (often), retroperitoneal hematoma, or pseudoaneurysm of the renal artery (rare). The extent of renal injury depends on the number of shock waves, shock wave energy, size and location of the stone. Risk factors of the patient for retroperitoneal hematoma are coagulation disorders, platelet dysfunction, use of antiplatelet agents (aspirin) or arterial hypertension.

Urinary tract obstruction:

Fragments of disintegrated stones may obstruct the ureter ("Steinstraße") and cause urinary colic.

Infections:

Urinary tract infection with fever. Urosepsis is possible, especially together with upper urinary tract obstruction.

Renal Failure:

Renal failure is a rare complication after ESWL, caused by the combination of the abovementioned complications. Very rarely, a nephrectomy is necessary due to complications (loss of kidney function, renal abscess, or massive hemorrhage).

References

Chaussy u.a. 2002 CHAUSSY, C. ; SCHMIEDT, E. ; JOCHAM, D. ; BRENDEL, W. ; FORSSMANN, B. ; WALTHER, V.: First clinical experience with extracorporeally induced destruction of kidney stones by shock waves. 1981.
In: J Urol
167 (2002), Nr. 5, S. 1957–60

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