In renal stone disease which is least resistant to lithotripsy
a. Stone composition is relevant to the success of SWL.
b. Calcium oxalate monohydrate, calcium phosphate and cystine stones are more difficult to fragment.
c. There are many different types of lithotriptors available, which are usually characterized by the types of lithotriptors available, which are usually characterized by the type of shockwave generator: e/ectrohydraulic, electromagnetic or piezoelectric.
d. The shockwaves are focused on the stone by an ellipsoid reflector; imaging is by fluoroscopy and/or ultrasound.
Mechanism of Action of SWL
a. As the shockwave strikes the anterior surface of the stone, it splits into two components.
b. One is reflected back towards the source, the other enters the stone.
c. These opposing forces create a pressure gradient producing fragmentation and erosion.
d. A similar phenomenon occurs as the shockwave strikes the posterior surface.
e. Cavitation is an acoustic phenomenon in which pressure change causes the rapid expansion of gas bubbles in a liquid medium.
f. These unstable bubbles collapse explosively forming microjets, which strike the stone at high velocities causing erosions and microscopic fractures.
Renal Calculi: Stones less than 2cm in diameter have up to a 90% chance of fragmentation and clearance.
a. Stones in the lower pole or in calyceal diverticula give lower success rates.
Bladder Calculi: can be treated with the patients prone.
b. Stone size is a very important factor. Renal calculi 2cm or less and ureteric calculi 1 cm or less in diameter are the ideal stone sizes for SWL.
c. Renal calculi between 2 and 3 cm in diameter may be treated after placement of a ureteric stent, but stone free rates are poor and the risk of complication increases.
d. Larger stones are best treated by PCNL. Treatment staghorn calculi is indicated only in rare cases with a normal collecting system and a relatively low stone burden.
Special Cases And Limitation
a. Children usually require general anaesthesia.
b. Treatment of stones over the sacro iliac joint may damage the epiphyseal plates and cause skeletal growth disturbances.
c. Anomalous Kidneys can safely be treated with SWL.
d. The prone position is recommended in pelvic kidneys; in horseshoe kidney stone visualization can be a problem because of the overlying bony skeleton.
e. In solitary kidneys stent placement is recommended for stones> 7mm in diameter.
f. Aneurysms: of the abdominal aorta and renal artery need caution, using intensive haemodynamic monitoring.
g. Cardiac pacemakers are not distributed by SWL.
h. Obesity can make imaging difficult. Most machines have limits.
Some long-term studies show an 8.2% prevalence of new onset hypertension after SWL. This is controversial.