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3rd year board in urology
High-energy shockwaves have been recognized for many years. Example of high-
energy shockwaves is the potentially window shattering sonic boom created when
aircraft pass beyond the speed of sound.
Engineers at Dornier Medical Systems during research on the effects of shockwaves
on military hardware to determine if the shockwaves striking the wall of a military
tank would damage the lungs of enemy member,discovered the possibility of safely
applying shockwave energy to human tissue when an engineer touched a target
body by chance. The engineer felt a sensation similar to an electric shock,
although the contact point at the skin showed no damage at all. In the course of
this effort the engineers discovered that shockwaves generated in water could
pass through living tissue (except for the lung) without damage but that brittle
materials in the path of the shockwaves would be fragmented.
• shockwave is generated by an
underwater spark discharge.
• For the shockwave to be focused
onto a calculus the electrode is
placed at one focus (termed F1)
of an ellipsoid, and the target
(the kidney stone) is placed at
the other focus (termed F2).
• Disadvantages are the
substantial pressure fluctuations
from shock to shock and a
relatively short electrode life.
An electrical current pass
through conductors producing
strong magnetic field moving the
plate against the water and
thereby generating a pressure
The energy in the shockwave is
concentrated onto the target by
focusing it with an acoustic lens.
Advantage: Introduction of
energy into the patient’s body
over a large skin area, which
may cause less pain.
These generators are made of a ceramic
elements each of which can be induced to
rapidly expand by the application of a
high-voltage pulse.The piezoelectric
elements are usually placed inside of a
spherical dish to permit convergence of
The advantages include the focusing
accuracy, a long service life, and the
possibility of an anesthetic-free
treatment because of the relatively low
energy density at the skin entry point of
1.Fluoroscopy Alone :
Advantages of fluoroscopy include its familiarity to most urologists, the
ability to visualize radiopaque calculi throughout the urinary tract, the
ability to use iodinated contrast agents to aid in stone localization, and
the ability to display anatomic detail.
The disadvantages include the exposure of the staff and patient to
ionizing radiation, the high maintenance demands of the equipment, and
the inability to visualize radiolucent calculi without the use of
radiographic contrast agents.
2. Ultrasonography Alone
Advantages: is inexpensive to manufacture and to maintain compared
with fluoroscopic systems. Another advantage is in the treatment of
children and infants when one is concerned about the dose of ionizing
radiation. In addition, ultrasonography can localize slightly opaque or
Disadvantages: requires a highly trained operator. It is almost impossible
to view a stone in areas such as the middle third of the ureter or when
there is an indwelling ureteral catheter. Once a stone is fragmented, it is
difficult to identify each individual stone piece.
3. Combination of Ultrasonography
In some cases combining ultrasonography and fluoroscopy for stone
localization are clearly advantageous but each system has a drawback
that limits one of the functions of the system.
A typical shockwave involves an initial
short compressive front with
pressures of about 40 MPa that is
followed by a longer, lower-amplitude
negative (tensile) pressure of 10 MPa,
with the entire pulse lasting for a
duration of 4 µsec.The ratio of the
positive to negative peak pressures is
Once the shockwave enters the
stone it will be reflected at sites
of impedance mismatch. One
such location is at the distal
surface of the stone at the stone-
fluid (urine) interface. As the
shockwave is reflected, it is
inverted in phase to a tensile
(negative) wave. If the tensile
wave exceeds the tensile
strength of the stone, there is an
induction of microcracks that
eventually coalesce, resulting in
stone fragmentation, which is
2- Squeezing-splitting or
The shockwave advances faster
through the stone than in the
fluid outside the stone. The
shockwave that propagates in
the fluid outside the stone
produces a circumferential force
on the stone, resulting in a
tensile stress in the stone that is
at its maximum at the proximal
and distal ends of the stone
3- shear stress
The shock waves propagate
through the stone and will result
in regions of high shear stress
inside the stone. Many materials
are weak in shear, particularly if
they consist of layers, because
the bonding strength of the
matrix between layers often has
a low ultimate shear stress.
The shockwave that is reflected
at the distal surface of the stone
can be focused either by
refraction or by diffraction from
the corners of the stone.
During the negative pressure
wave, the pressure inside the
bubble falls below the vapor
pressure of the fluid, and the
bubble fills with vapor and grows
rapidly in size (almost three
orders of magnitude)and then
collapse violently, giving rise to
high pressures and temperatures.
6- Dynamic fracture
the damage induced by SWL
accumulates during the course of
the treatment, leading to the
eventual destruction of the
1. Acute Extrarenal Damage
visceral injuries, such as perforation of the colon, hepatic hematoma,
splenic rupture, pancreatitis, and abdominal wall abscess.
Extrarenal vascular complications such as rupture of the hepatic artery,
rupture of the abdominal aorta, and iliac vein thrombosis.
Thoracic events, such as pneumothorax and urinothorax.
shockwaves could induce cardiac arrhythmia, an observation that led to
electrocardiographic synchronization with R-wave triggering on the
Dornier HM3 device.
The development of diabetes was related to the total number of
shockwaves and the power level of the lithotripter.
2. Acute Renal Injury
Hematuria is so common that it may be considered an incidental finding,
and its severity is rarely of concern. Although hematuria was initially
considered to be a consequence of irritation of the urothelium as stones
were fragmented by shockwaves, it is now known that shockwaves
rupture blood vessels and can damage surrounding renal tubules .
• unsatisfactory control of their hypertension at the time of SWL
• diabetes mellitus
• coronary artery disease
3. Chronic Renal Injury
accelerated rise in systemic blood pressure because
1. subcapsular hematomas can induce hypertension, such changes are
2. Mesangial proliferation after SWL could induce hypertensive changes
decrease in renal function
increase in the rate of stone recurrence (Stone recurrence rates may be
higher after SWL because of residual stone debris)
induction of brushite stone disease.
wider focal width increase the likelihood of stone breakage because the kidney
tends to move, as a consequence of respiratory motion, the stone may move in
and out of a narrow focal zone.
Optimal coupling permits the efficient transfer of energy from the lithotripter
to the patient; poor coupling will reduce stone breakage. Most commonly,
energy transfer through a coupling medium is attenuated by air pockets in the
coupling interface itself.
Decrease the rate of shockwaves because the dynamic bubbles are given a
longer time interval to dissipate with a slower rate and therefore have less of a
shielding effect and energy draw from subsequent shocks.
Decrease the energy setting on the machine. Increasing the power setting on
most electromagnetic lithotripters actually narrows the focal zone which
decreases stone breakage and may also increase the risk of renal injury.
To reduce stone motion, urologists can perform SWL with general anesthesia,
which will control the patient’s respiratory rate and volume.
1. in 1980s regional or general anesthesia was used in all instances because
the unmodified HM3 device produced a powerful shockwave and
treatment at recommended energy levels caused intolerable pain.
2. Short-acting agents, such as the narcotic alfentanil and the sedative-
hypnotics midazolam and propofol can be used in various combinations to
allow most SWL treatments with any lithotripter.
3. topical agents e.g.EMLA cream, a mixture of lidocaine and prilocaine, has
been shown to reduce anesthesia requirements during SWL . EMLA cream
should be applied at least 45 minutes before SWL.
4. Children and extremely anxious individuals may be served best by
general anesthesia. Patients who received general anesthesia
experienced a significantly greater stone-free rate than did those
patients who underwent intravenous sedation. Possible explanation for
this is the more controlled respiratory excursion that is conferred by the
Safe shock wave dosage is unknown. Shock waves induce trauma,
including intrarenal and perirenal hemorrhage and edema, and thus the
minimal shocks needed to achieve fragmentation should be given.
Determination of adequate fragmentation during treatment may be
difficult. Initial sharp edges become fuzzy or blurred .Stones that were
initially visualized may disappear after successful fragmentation.
Intermittent visualization ensures accurate focusing and assessment of
progress and eventual termination of the procedure.
The reasons for poor clearance
of fragments from the lower pole
after SWL are unclear. The
gravity-dependent position of
the lower pole calyx may impede
the passage of stone
fragments,The examination of
the angle formed between the
lower infundibulum and the renal
pelvis and if the angle greater
than 90 degrees it should
facilitate drainage of fragments
from the lower pole.
2. uncorrected blood clotting disorders (including anticoagulation)
3. known renal artery stenosis
4. Acute UTI or urosepsis
5. Uncorrected obstruction distal to the stone
6. Abdominal aortic aneurysm
1. Uncontrolled HT
2. Morbid obesity
3. Renal ectopy or malformation
4. Renal insuficiency
5. Cardiac pacemaker
Patients should be encouraged to maintain an active ambulatory status
to facilitate stone passage.
Fluid intake should be encouraged.
Severe pain unresponsive to routine intravenous or oral medications
should alert the physician for perirenal hematomas. In such a situation,
CT scan should then be undertaken to stage the injury.
Steinstrasse (stone street) Asymptomatic individuals can be followed up
with serial KUBs and ultrasonography. Severe pain or fever requires
intervention. Percutaneous nephrostomy drainage is usually
uncomplicated owing to the associated hydronephrosis. Decompressing
the collecting system allows for effective coaptation of the ureteral walls
and encourages resolution of the problem. If steinstrasse does not resolve
,retrograde endoscopic manipulations is required.