ESWL Flashcards
components lithotriptor
energy source
focusing system - concentrate energy on stone
coupling mechanism - gel or water filled cushion transmit energy
imaging
types of energy courses
EHL
PE
EM
focusing mechnaisms
EM = cylindrical reflector EHL = elliptical PE = hemi spherical
how EM ESWL works
coil of wire in close contact with metal membrane
current through coil which repulses metal membrane generates a pressure in water
focused by an aoustic lens
PE ESWLworks
PE elements produce electrical discharge under stress or tension
energy transimission via movemet of the source when electricity is passed through it
placed on a concave surface which focuses the waves onto stone
electrohydraulic ESWL works
spark between two electrodes under water
results in rapid expansion and collapse gas bubble
subsequent energy transmission
requires aqueous irrigations, not saline or glycine
ultrasonic lithotripsy
us waves prodcued by a generator transmitted down hollow probe
resulting in vibration probe tip
contact with stone causes drilling and breakage
not for use in ureter as tip vibration causes heat production
ultrasonic lithotripsy
us waves prodcued by a generator transmitted down hollow probe
resulting in vibration probe tip
contact with stone causes drilling and breakage
not for use in ureter as tip vibration causes heat production
ballistic lithotripsy
forward momentum of a metal rod placed in contact with stone surface
ballistic lithotripsy
forward momentum of a metal rod placed in contact with stone surface
swiss lithoclast action
controlled burst of compressed air to move a projectile
tends to move stones forward
mast combines ballistic and suction
often used in pcnl
shockwave phases
2 main phases
short positive phase causing erosion and entry and exit points of stone
internal shattering due to compressive effects of wave
second longer negative pressure phase = tensile phase which results in formation of microbubbles which collapse and form microjets which further erode stone
EH spark gap
Spark created between 2 electrodes 1mm apart under water
Water around electrode forms gas bubble
Rapid expansion & release of bubble generates shock wave
Focused by a metal reflector (hemi-ellipsoid)
PE generator
Spherical dish covered with 3000 small polycrystalline ceramic elements
Each expands rapidly when high voltage applied across them
Rapid expansion generates a shock wave
Spherical dish allows convergence of shock wave. Focus is centre
direct 3 and indirect 2 effects eswl on stone
direct
fragmentation
shearing
spallation
indirect
cavitation
dynamic squeezing
where different stone fracture mechanisms act
incident SW hits stone
cavitation occurs at site of entry i.e. proximal
squeezing occurs at the equators of the stone
spall is dstial
superfocusing internal caustic
spallation
reflected tensile wave at distal surface of stone with maximum tension there, breaking the stone form the inside similar to freezing water in brittle materal
cavitation mechanism
negative pressure waves induce a collapsoing cavitation bubble at stones front surface, micro explosive erosion mainly at proximal end of stone
super focusing or tear and shear forces
pressure gradients resulting from impedance changes at the front of the stone and the distal surface with pressure inversion,
hammer like action, resulting in crater like fragmentation at both ends of stone
dynamic squeezing
pressure gradient between circumferential and long waves resultsin squeezing of stone, nut cracker like action which splits the stone
dorneir HM3 EHL
spark plug located a tthe focus of the brass ellipsoidal reflector
energy from spark plug reflected and focused to second focus of the reflector
EM lithotriptor two types
acousitc lengs
cynlindrical membrane
Siemens or Dornier
membrane driven by a coil to produce a plane wave focused by acoustic lens
Storz, coil excites a cylindrical membrane which generates a wave that is focused by a parabolic reflector
wolf PE 3000
PE elements on a semi spherical backing
point of power ramping
renal vasoconstriction
A ramping protocol has also been shown to improve stone
comminution and decrease renal injury
The protective mechanism of ramping is thought to be vasoconstrictive
Initial studies recommended that a 3- to 4-minute pause was key to the protective effects of the ramping protocol
However, as long as the kidney
is allowed to acclimate to the lower power setting for 3 to 4
minutes, the ramping protocol can omit the pause.
shocks used
3500 shocks
frequency
0.5-1Hz
Oxford 1Hz for total of 2000 shocks starting at 1J and increase slowly to energy level 6, aim energy 6 in kidney and 8 in ureter
contraindications ESWL
pregnancy bleeding unctonrolled hypertension infection distal obstruction arterial aneurysm in vicinity
relative
hard stones
morbid obesity
abdominal pacemaker
consent for lithotripsy
10-50% need more than one treatment need other treatment pain blood in urine recurrence stone
2-10% infection
bruisiing
surgical removal fragments
<1%
perirenal haematoma
severe infection
damage to lung or pancreas
