extracarporial lithotripcy

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2. Extracorporeal
Shockwave Lithotripsy
(ESWL)
Presented by:
Dr. Afia Tehreem Gilanee
Resident Urology
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3. OBJECTIVES
Introduction To ESWL
Working Principle of a Lithotripter
Shockwave Physics
Types of Shockwave Sources
Pre-operative, Intraoperative And Post-operative Aspects
of SWL
EAU Guidelines On SWL
Take-home Message
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4. INTRODUCTION TO ESWL
A non invasive medical procedure used to treat
certain types of kidney stones
To break down kidney stones into smaller
fragments, allowing them to pass more easily
through urinary tract and be eliminated from body
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5. WORKING PRINCIPLE OF A LITHOTRIPTOR
1. Energy source- creates shock waves
2. Coupling Mechanism- transfers the energy
from outside to inside the body
3. Modes (fluoroscopic, ultrasonic or both)-
identifies and positions the calculus at focus
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6. LITHOTRIPTORS
Differ on the basis of
 Focal peak pressures (400-1500 bar)
 Focal dimensions (6*28mm to 50*15mm)
 Varied distances (12-17cm) between shockwave source and the target
 Generated pain
 Anaesthetic requirement
 Size
 Mobility
 Cost
 Durability
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7. LITHOTRIPTORS (Contd.)
The success rate of SWL- depends on the efficacy of
lithotripter and on
o size, location, and composition (hardness) of stones
o patient’s habitus
o performance of SWL
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8. SHOCKWAVE PHYSICS
Acoustic shockwaves – non harmonic
Non linear pressure characteristics
Steep rise in pressure amplitude –
compressive forces
2 basic types of shockwave sources
• Supersonic emitters
• Finite amplitude emitters
✓Piezoceramic
✓Electromagnetic
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9. SUPERSONIC EMITTERS
Release energy in a confined space – producing an
expanding plasma and an acoustic shockwave
Initial compression wave travels faster than speed of
sound in water
Rapidly slows down
Analogous to thunderstorm in nature
Can successfully fragment the calculi
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10. FINITE-AMPLITUDE EMITTERS
Create pulsed acoustic shockwaves
By displacing a surface activated by electrical
discharge
Piezoceramic-shockwaves after an electrical discharge
causes ceramic component to elongate- surface
displaced and acoustic pulse generated
Thousands of such components placed on concave
side of spherical surface directed towards a focus
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12. FINITE-AMPLITUDE EMITTERS (Contd.)
Electromagnetic systems-
electric discharge to a slab,
adjacent to an insulating
foil, creates an electric
current that repulses a metal
membrane – displacing it
and generating an acoustic
pulse in an adjacent medium
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15. FRAGMENTATION
Achieved by erosion and shattering
Erosion at entry and exit sites of shockwaves
Shattering –from energy absorption
Surrounding biologic tissues- resilient because neither brittle
nor focused
Acoustic energy focusing (AEF) devices- attach to the stones
External energy source- AEF device expands and cavitates-
fragmentation
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16. PREOPERATIVE EVALUATION
Vital signs monitoring
Physical examination
Investigations (X-ray KUB, USG)
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17. INTRAOPERATIVE ASPECTS
A.Stone Localization
➢ Proper patient positioning- pre requisite
➢Anteriorly located kidneys, medially oriented
portions of horseshoe kidney, or transplant
kidneys- best treated in prone position
➢Retrograde stents- easy identification
➢IV contrast agents- helpful in localization
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18. INTRAOPERATIVE ASPECTS (Contd.)
B. Imaging
1. Flouroscopic Imaging
• Dimmed room lighting and decreased radiation exposure
• Intermittent fluoroscopy- reveals movement with respiration
2. Ultrasonic Imaging
• Eliminates radiation exposure
• Can identify radiolucent or small caculi
• Ureteral or medially located ones- difficult esp if non obstructive
• Localization is difficult in obese
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19. INTRAOPERATIVE ASPECTS (Contd.)
C. Coupling
• Coupling devices- properties similar to those of
human skin
• Prevent pain, ecchymoses, hematomas, or skin
breakdown
• Water cushion coupling systems
• Coupling gel like those in USG
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20. INTRAOPERATIVE ASPECTS (Contd.)
D. Shockwave Triggering and Fragmentation
• Initially shockwaves were triggered with ECG
• Decrease the shockwaves during repolarization when
myocardium is most sensitive
• Shockwaves- trauma, including intrarenal and perirenal
hemorrhage and edema
• Minimal shocks should be delivered
• Determination of adequate fragmentation- Sharp edges
become fuzzy or blurred
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21. EAU GUIDELINES FOR SWL
 Routine use of internal stents before SWL does not improve stone-free
rates; however may reduce formation of steinstrasse
 Patients with a pacemaker can be treated with SWL
 Patients with implanted cardioverter defibrillators- special care;
 Starting SWL on a lower energy setting with stepwise power ramping
prevents renal injury
 Optimal shockwave frequency- 1-1.5Hz
 Repeat sessions feasible within 1 day for ureteral stones
 No standard antibiotic prophylaxis prior to SWL recommended
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22. POST-OPERATIVE CARE
Fluid intake should be encouraged
Asymptomatic individuals- Follow up- serial X ray KUB and
USG
Steinstrasse or stone gravel accumulation in ureter – severe
pain or fever
PCN drainage and decompressing the collecting systems
If uneffective- retrograde endoscopic manipulations
Severe pain unresponsive to routine IV or oral medications-
rare perirenal hematomas- CT scan for staging
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23. CONTRAINDICATIONS OF SWL
Pregnancy
Bleeding disorders (should be compensated 24hrs before and
48hrs after treatment)
Untreated UTIs
Severe skeletal malformations and severe obesity, (prevent
targeting of stone)
Arterial aneurysm in the vicinity of stone
Anatomical obstruction distal to the stone
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24. TAKE-HOME MESSAGE
Approximately 75% of patients treated with SWL- stone free in 3
months
Large pelvic stones (>1.5cm)- stone free rates at 3 months- 75%
Vs lower calyx- 35%
Small pelvic stones (<1.5cm)- stone free rate- 90%
Vs middle calyx(75%) or lower calyx (50%)
Increasing the size of stones- stone free rates decrease (more so in
lower and middle calyces than superior calyceal and pelvic locations)
Lower calyceal stone free rates- increased with small stone burden, a
short and wide infundibulum, and a non-acute infundibulo-pelvic angle
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Thank You!