2. EXTRACORPOREAL SHOCK WAVE
LITHOTRIPSY
ESWL is an alternative treatment for the disintegration of renal stones in the non–lower pole of the
kidney and the upper part of the ureter.
Although ESWL was considered the treatment of choice for these types of stones, it has been
surpassed in the United States by URS.
In symptomatic patients with stone burdens smaller than 20 mm, ESWL is still an effective
treatment; however, when compared with URS, it is associated with a higher likelihood of repeat
procedures.
Successful treatment with ESWL depends upon several factors:
Obesity
skin-to-stone distance
collecting system anatomy
stone composition
stone density/attenuation
3. Old Vs. New Generations
The original first-generation lithotripter (Dornier HM-3) required immersion of the patient into a
water bath, which could result in significant effects in the cardiovascular and respiratory systems
Newer generations of lithotripters use less power and have eliminated the water bath,
therefore the efficiency of stone fragmentation is decreased, resulting in higher retreatment rates
4. Biomechanical Effects of Shock Wave Therapy
For ESWL shock waves to be effective, there should be no movement of stones during treatment.
Otherwise treatment time will be prolonged, adjoining tissues may become injured from the energy
of the shock waves.
Using controlled ventilation during a general anesthetic may cause stone excursion to surpass 60
mm.
Spontaneous ventilation has been observed to displace stones over 12 mm, whereas in patients
with adequate sedation, stone excursion is limited to approximately 5 mm.
5. Preparations
For effective stone disintegration, shock waves should reach the stone unimpeded.
The flank area should be kept free of any medium that would provide an interface for the dissipation of
shock wave energy.
Nephrostomy dressings should be removed, and the nephrostomy catheter should be taped clear of the
blast path.
Although shock waves they do cause tissue injury, the extent of which depends on the tissue exposed
and the shock wave energy at the tissue level.
Skin bruising and flank ecchymoses can occur at the entry site.
Painful hematoma in the flank muscles may also occur.
Hematuria is almost always present at the end of the procedure and results from shock wave–induced
endothelial injury to the kidney and ureter.
Adequate hydration is necessary to prevent clot retention.
6. Cardiac Dysrhythmias
Shock wave–induced cardiac dysrhythmias were previously reported in 10% to 14% of patients
undergoing immersion lithotripsy
Depending on the technology of the newer generations of lithotripters:
some authors have observed dysrhythmias in 20% to 59% of patients with piezoelectric source of shock
waves versus 1.4% to 9% using electromagnetic lithotripters
These dysrhythmic episodes do not seem to be of any clinical significance.
Artifacts on the electrocardiogram also are common.
Artifacts and dysrhythmias usually disappear when the lithotripsy is stopped.
7. Anesthetic Choices for Lithotripsy
Historically, anesthetic regimens used successfully for immersion lithotripsy included general
anesthesia, epidural anesthesia, spinal anesthesia, flank infiltration with or without intercostal
blocks, and analgesia-sedation, including patient-controlled analgesia.
With the newer generations of lithotripters, most analgesia-sedation combinations are adequate.
Even patient-controlled analgesia with alfentanil and a combination of propofol and alfentanil has
been used.
Many centers routinely use general anesthesia with short-acting inhaled or intravenous anesthetics
and use laryngeal mask airway for ventilation.
8. Newer Generations of Lithotripters
Newer generations of lithotripters have no water bath, and tend to use multifunctional tables that
allow other procedures, such as cystoscopy and stent placement, to be accomplished without
moving the patient off the table.
The shock waves are tightly focused; therefore, they cause less pain at the entry site, and
intravenous analgesia-sedation is the mainstay of anesthesia with these newer lithotripters.
Other incidental interventions, such as cystoscopy, stone manipulation, or stent placement, may
alter anesthetic requirements.
Because these newer lithotripters have a much smaller focal zone for the shock waves, it is essential
that adequate analgesia and sedation be provided so that stone excursion with respiration is limited
to the focal zone.
9. Contraindications
Pregnancy, active urinary tract infection, and untreated bleeding disorders are the major
contraindications to lithotripsy.
Women of childbearing age must have a pregnancy test that is documented to be negative before
lithotripsy.
Standard tests of coagulation, such as the platelet count, prothrombin time, and partial
thromboplastin time, should be obtained as indicated by medical history.
Pacemakers, automatic implanted cardioverter-defibrillators (AICDs), abdominal aortic aneurysm,
orthopedic prostheses, and obesity are no longer considered contraindications.
10. Contraindications
Alternative means of Orthopedic prostheses, are not a problem if they are not in the blast path.
Positioning of obese patients may be problematic at times. Not only do extremely obese patients
present anesthetic challenges related to obesity, but also focusing of the stone may be extremely
difficult in the very obese.
It is prudent for focusing of the stone to be attempted before administering any anesthetic in this
highrisk population.
