Stone fragmentation techniques: extracorporeal lithotripsy (ESWL) The
technique of focusing externally generated shock waves at a target (the stone).
First used in humans in 1980. The first commercial lithotriptor, the Dornier
HM3, became available in 1983.13 ESWL revolutionized kidney and ureteric stone
treatment. Three methods of shock wave generation are commercially
available—electrohydraulic, electromagnetic, and
piezoelectric.
Electrohydraulic Application of a high voltage
electrical current between 2 electrodes about 1mm apart under water causes
discharge of a spark. Water around the tip of the electrode is vaporized by the
high temperature resulting in a rapidly expanding gas bubble. The rapid
expansion and then the rapid collapse of this bubble generates a shock wave
which is focused by a metal reflector shaped as a hemi-ellipsoid. Used in the
original Dornier HM3 lithotriptor.
Electromagnetic Two electrically
conducting cylindrical plates are separated by a thin membrane of insulating
material. Passage of an electrical current through the plates generates a strong
magnetic field between them, the subsequent movement of which generates a shock
wave. An acoustic lens is used to focus the shock
wave.
Piezoelectric A spherical dish is covered with about 3000 small
ceramic elements, each of which expands rapidly when a high voltage is applied
across them. This rapid expansion generates a shock wave. X-ray, ultrasound,
or a combination of both are used to locate the stone on which the shock waves
are focused. Older machines required general or regional anaesthesia because the
shock waves were powerful and caused severe pain. Newer lithotriptors generate
less powerful shock waves, allowing ESWL with oral or parenteral analgesia in
many cases, but they are less efficient at stone fragmentation.
Efficacy
of ESWL Likelihood of fragmention with ESWL depends on stone size and
location, anatomy of renal collecting system, degree of obesity, and stone
composition. Most effective for stones <2cm in diameter, in favourable
anatomical locations. Less effective for stones >2cm diameter, in lower pole
stones in a calyceal diverticulum (poor drainage), and those composed of cystine
or calcium oxalate monohydrate (very hard). Stone free rates for solitary
kidney stones are 80% for stones <1cm in diameter, 60% for those between 1
2cm, and 50% for those >2cm in diameter. Lower stone free rates as compared
with open surgery or PCNL are accepted because of the minimal morbidity of
ESWL. There have been no randomized studies comparing stone free rates
between different lithotriptors. In non-randomized studies, rather surprisingly,
when it comes to efficacy of stone fragmentation, older (the original Dornier
HM3 machine) is better (but higher requirement for analgesia and sedation or
general anaesthesia). Less powerful (modern) lithotriptors have lower stone free
rates and higher retreatment rates.
Side-effects of ESWL ESWL causes a
certain amount of structural and functional renal damage (found more frequently
the harder you look). Haematuria (microscopic, macroscopic) and oedema are
common, perirenal haematomas less so (0.5% detected on ultrasound with modern
machines, although reported in as many as 30% with the Dornier HM3). Effective
renal plasma flow (measured by renography) has been reported to fall in ~30% of
treated kidneys. There is data suggesting that ESWL may increase the likelihood
of development of hypertension. Acute renal injury may be more likely to occur
in patients with pre-existing hypertension, prolonged coagulation time,
coexisting coronary heart disease, diabetes, and in those with solitary
kidneys.
BAUS procedure-specific consent form: potential
complications after ESWL Common - Bleeding on passing urine for short
period after procedure - Pain in the kidney as small fragments of stone pass
after fragmentation - UTI from bacteria released from the stone, needing
antibiotic treatment.
Occasional - Stone will not break as too hard,
requiring an alternative treatment - Repeated ESWL treatments may be
required - Recurrence of stones.
Rare - Kidney damage (bruising) or
infection, needing further treatment - Stone fragments occasionally get stuck
in the tube between the kidney and the bladder requiring hospital attendance and
sometimes surgery to remove the stone fragment - Severe infection requiring
intravenous antibiotics and sometimes drainage of the kidney by a small drain
placed through the back into the kidney.
Alternative
therapy Telescopic surgery, open surgery, or observation to allow spontaneous
passage.
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