Urolithiasis management- eswl

1. EXTRACORPOREAL SHOCKWAVE
LITHOTRIPSY
Dept of Urology
Govt Royapettah Hospital and Kilpauk Medical College
Chennai
1

2. Moderators:
Professors:
• Prof. Dr. G. Sivasankar, M.S., M.Ch.,
• Prof. Dr. A. Senthilvel, M.S., M.Ch.,
Asst Professors:
• Dr. J. Sivabalan, M.S., M.Ch.,
• Dr. R. Bhargavi, M.S., M.Ch.,
• Dr. S. Raju, M.S., M.Ch.,
• Dr. K. Muthurathinam, M.S., M.Ch.,
• Dr. D. Tamilselvan, M.S., M.Ch.,
• Dr. K. Senthilkumar, M.S., M.Ch.
Dept of Urology, GRH and KMC,
Chennai.
2

3. PHYSICS
• An acoustic wave, or sound wave, is created whenever
an object moves within a fluid (a fluid can be either a
gas or liquid)
• Abrupt release of energy in a small space- high energy
amplitudes – shock waves
• Shockwaves thro substances of differing impedance –
compressive stresses at boundary surface
• IMPLOSION rather than explosion
3
Dept of Urology, GRH and KMC,
Chennai.

4. Shock wave
• It represents a short-
duration (<10μs)
acoustic pressure wave
consisting of a
compressive phase
(peak pressure: 30–
100MPa) followed by a
tensile phase (negative
pressure)-10mpa
• 150–800 kHz
4
Dept of Urology, GRH and KMC,
Chennai.

5. • Goal of SWL is to pulverize kidney stones into
gravels for spontaneous discharge in urine
without inflicting adverse effects to
surrounding tissues
5
Dept of Urology, GRH and KMC,
Chennai.

6. LITHOTRIPTOR
• shock‐wave generator
• focusing device
• coupling medium
• stone localization system.
6
Dept of Urology, GRH and KMC,
Chennai.

7. SHOCK WAVE GENERATOR
• Electrohydraulic (spark gap)
• Electromagnetic
• Piezoelectric
7
Dept of Urology, GRH and KMC,
Chennai.

8. • ELECTROHYDRAULIC (SPARK GAP)
GENERATOR
• shockwave is generated by an underwater
spark discharge
• generate a strong converging acoustic wave
• shockwave focused onto a calculus - ellipsoid
reflector
8
Dept of Urology, GRH and KMC,
Chennai.

9. 9
Dept of Urology, GRH and KMC,
Chennai.

10. • Advantage
• Very effective in breaking kidney stones
• Disadvantages
• Pressure fluctuations from shock to shock
• Short electrode life
10
Dept of Urology, GRH and KMC,
Chennai.

11. ELECTROMAGNETIC GENERATOR
• Two conducting cylindrical plates separated by a
thin insulating sheet
• plane or cylindrical shockwave
• Cylindrical waves - Focused by acoustic
lens/parabolic reflector
11
Dept of Urology, GRH and KMC,
Chennai.

12. Electromagnetic shockwave generator 12
Dept of Urology, GRH and KMC,
Chennai.

13. • ADVANTAGES
• more controllable and reproducible than electrohydraulic
generators
• Less pain (introduction of energy over a large skin area)
• Small focal point with high-energy densities (very effective
in breaking stones)
• No need for frequent electrode replacement
• DISSADVANTAGE
• Increased rate of subcapsular hematoma
• (small focal point of high energy)
13
Dept of Urology, GRH and KMC,
Chennai.

14. PIEZOELECTRIC GENERATOR
• small, polarized, polycrystalline, ceramic
elements (barium titanate) - induced by
application of high‐voltage (1–10 kV) –
generate a strong converging acoustic wave
• Focused by center of the spherical dish
14
Dept of Urology, GRH and KMC,
Chennai.

15. Piezoelectric shockwave generator - polarized
polycrystalline ceramic elements in spherical dish 15
Dept of Urology, GRH and KMC,
Chennai.

16. • Advantages
• High focusing accuracy
• Long service life
• No need for anesthesia- low energy density at the
skin entry point
• Disadvantage
• low energy density, reduces effectiveness of
breaking stones
16
Dept of Urology, GRH and KMC,
Chennai.

17. FOCUSSING SYSTEMS
• Electrohydraulic – Ellipsoid
• Piezo-electric – Hemispherical dish
• Electromagnetic – acoustic lens (Siemens)
• Parabolic (Storz)
17
Dept of Urology, GRH and KMC,
Chennai.

18. 18
Dept of Urology, GRH and KMC,
Chennai.

19. OTHER GENERATORS
• Microexplosive generators
• explosion of tiny lead azide pellets within a parabolic
reflector generates –shockwave
• storage , handling of the volatile lead azide pellets-
difficult
• Laser beam
• Multistage light gas gun
• Not successful commercialy
19
Dept of Urology, GRH and KMC,
Chennai.

20. CHARACTERISTICS OF A LITHOTRIPTOR
SHOCK WAVE
 wave is a short pulse of about 5--10 μs duration
 consists of positive pressure shock (compressive wave) with
pressures of about 40 MPa ,lasting about 1-2 μs
 followed by a longer, lower amplitude (tensile wave) negative
pressure of 10 MPa,lasts about 3-5 μs
• focal point is Ellipsoidal/cigar in shape, with its longest dimension
along the central axis of lithotripter
• Length and diameter of the focal zone depends on
– diameter of the source
– focal length
20
Dept of Urology, GRH and KMC,
Chennai.

21. • Intensity transmission of acoustic wave water
to tissue is very high
• water-to-stone transmission is high (75 to 95%
energy transmitted into the stones)
• water-air - 99.9% reflected (shock wave
generators in lithotripsy are water-filled)
21
Dept of Urology, GRH and KMC,
Chennai.

22. The ideal lithotripter
• moderate positive peak pressure, p+
• sufficient disintegration power (effective
energy, E12mm) to disintegrate hard stones
and to compensate or shock‐wave attenuation
(obesity)
• minimal cavitation effects and hence minimal
risk of adverse tissue effects.
22
Dept of Urology, GRH and KMC,
Chennai.

23. SHOCK WAVE COUPLING MEDIUM
Dornier HM3 lithotripter
• Large water bath
• required general or spinal anesthesia
• Second generation lithotriptor
• water cushion or partial water bath
• Third‐generation lithotripters
• Allow anesthesia‐free treatments.
• both fluoroscopy and ultrasound,use possible
• both SWL and endourologic procedures are
possible(multifunctional system)
• Facilitates prone position
• (middle ureter, horseshoe kidneys, or pelvic kidneys)
23
Dept of Urology, GRH and KMC,
Chennai.

24. IMAGING FOR STONE LOCALIZATION
• Ultrasonography
• Isocentric Fluoroscopy
• Combination of ultrasonography and
fluoroscopy
24
Dept of Urology, GRH and KMC,
Chennai.

25. Choice of the ideal lithotripter for any given stone center
• A multifunctional workstation for SWL and
endourologic procedures is the best choice for
centers with an adequate patient load in both
treatment modalities.
• An integrated or hybrid design makes economic
sense in very active stone centers.
• In centers with a modest patient load a modular
system may probably be the better choice
25
Dept of Urology, GRH and KMC,
Chennai.

26. ESWL-HISTORY
• Dornier HM I -1980
• HM II- 1982
• Dornier HM III – 1984
• Portable Dornier – 1996
• Dornier HM IV - 1997
26
Dept of Urology, GRH and KMC,
Chennai.

27. MECHANISM
27
Dept of Urology, GRH and KMC,
Chennai.

28. Traditional theories of stone fragmentation
• stress gradient and tensile failure at stone/ fluid boundaries
• Acoustic cavitations
• Squeezing Compression fracture
• quasi‐static squeezing(wide focus with lower pressure to enhance)
• Hopkins effect (cavitation and shear forces)
• Spallation
• Dynamic fatigue
• dynamic squeezing
28
Dept of Urology, GRH and KMC,
Chennai.

29. 29
Dept of Urology, GRH and KMC,
Chennai.

30. 30
Dept of Urology, GRH and KMC,
Chennai.

31. Spallation
• Reflected tensile wave at distal surface of the
stone with maximum tension at the distal part
of the stone
• Spalling will gradually become less effective as
the size of fragments decreases or in stones
with curved boundaries or when wave
attenuation in the stone material is high
• Breaking the stone from the inside
31
Dept of Urology, GRH and KMC,
Chennai.

32. Tear and shear
• Pressure gradients
resulting from
impedance changes at
the stone front and
distal surface with
pressure inversion
• Stone made of layers
• Hammer-like action
resulting in a crater-like
fragmentation
32
Dept of Urology, GRH and KMC,
Chennai.

33. Quasi-static squeezing
• Pressure gradient
between
circumferential and
longitudinal waves
results in squeezing of
the stone
• Nutcracker-like action
33
Dept of Urology, GRH and KMC,
Chennai.

34. cavitation
• Cavitation is defined as the
formation and collapse of
bubbles
• Negative pressure waves
induce a collapsing cavitation
bubble at the stone surface
• Microexplosive erosion at the
proximal and distal ends of
the stone
34
Dept of Urology, GRH and KMC,
Chennai.

35. Dynamic squeezing
• Shear waves initiated at the corners of the
stone and driven by squeezing waves along
the calculus lead to the greatest stress and
tension
• Nutcracker-like action in combination with
spalling
35
Dept of Urology, GRH and KMC,
Chennai.

36. • squeezing will be enhanced when the entire
stone falls within the diameter of the focal
zone
• If lithotripters have very small focal zones
this mechanism will be ineffective
36
Dept of Urology, GRH and KMC,
Chennai.

37. SUPERFOCUSING
Shockwave passed in to stone
get reflected at the distal surface of the stone
focused either by refraction or by diffraction from
the corners of the stone to interior of stone
fragmentation
37
Dept of Urology, GRH and KMC,
Chennai.

38. 38
Dept of Urology, GRH and KMC,
Chennai.

39. 39
Dept of Urology, GRH and KMC,
Chennai.

40. Unified mechanism
40
Dept of Urology, GRH and KMC,
Chennai.

41. A heuristic model of stone
comminution in SWL
1. P+(avg) (controlled by the output kV or energy
setting of the lithotripter) and
2 .dose of the shock waves delivered
• Effective treatment can be achieved by using
moderate P+(avg) in the range of 15–20 MPa
within 2000 shocks.
• progressive ramping of the lithotripter output
(and thus P+(avg)) that can achieve effective
stone comminution with minimal risk of tissue
injury
41
Dept of Urology, GRH and KMC,
Chennai.

42. 42
Dept of Urology, GRH and KMC,
Chennai.

43. AIM
• Fragment the stone to 1mm pieces- IDEAL
• <= 4 mm acceptable
• Clearance may take 3-4 weeks,varies among
patients
43
Dept of Urology, GRH and KMC,
Chennai.

44. CONTRAINDICATION
• Urinary Tract Infection
• Pregnancy
• Uncorrected Coagulopathy
• Arterial aneurysms in close proximity to target
stone
• Uncontrolled hypertension
• Distal obstruction
• Morbid Obesity
• Spinal Deformity or Limb Contractures
44
Dept of Urology, GRH and KMC,
Chennai.

45. SWL TREATMENT OF RENAL AND
URETERAL CALCULI
RENAL CALCULI
• To achieve maximal stone clearance with
minimal morbidity
45
Dept of Urology, GRH and KMC,
Chennai.

46. INDICATION
• Pain
• Infection
• Obstruction
46
Dept of Urology, GRH and KMC,
Chennai.

47. Stone size and location
• SWL stone‐free rates at 3 months are 86–89% for
renal pelvis, 71–83% for upper calyx, 73–84% for
middle calyx, and 37–68% lower calyx stones
• 10 mm or less - 74% ( 60 to 90%)
• 11 to 20 mm - 54% ( 50 to 83%)
• >20 mm - 33% ( 33 to 81%)
47
Dept of Urology, GRH and KMC,
Chennai.

48. 48
Dept of Urology, GRH and KMC,
Chennai.

49. SMALL, ASYMPTOMATIC CALYCEAL
STONES (<5mm)
Controversial
Most calyceal stones, in the absence of intervention, are likely
to increase in size, causing symptoms of pain or infection
prophylactic SWL - targeting may be difficult
Indication
pediatric patients
solitary kidney
High-risk professions ( pilots)
Women considering pregnancy
49
Dept of Urology, GRH and KMC,
Chennai.

50. TREATMENT DECISIONS BY STONE COMPOSITION
• Fragmentation by SWL is variable among stones
of different composition
• Cystine
• Brushite calculi
• Calcium oxalate monohydrate
• matrix
• most resistant to SWL, produce large pieces that
may be difficult to clear from the collecting
system
50
Dept of Urology, GRH and KMC,
Chennai.

51. • Brushite, cystine, calcium oxalate monohydrate
should be treated by SWL only when the stone burden
is small (<1.5 cm)
• Larger stones -- PNL or ureteroscopy
• Matrix calculi
• Radiolucent ,associated with urea-splitting bacteriuria
• SWL is not effective (gelatinous nature )
• PNL , ureteroscopy – choice
51
Dept of Urology, GRH and KMC,
Chennai.

52. PREDICTION OF STONE COMPOSITION
(STONE FRAGILITY)
• PLAIN X-RAY KUB - smooth-edged stones,
homogeneous, more dense than bone -- require
more shockwaves
• Round, radially reticulated stones with spiculated
edges or stones with irregular margin – good
fragmentation
• Accuracy - 39%
52
Dept of Urology, GRH and KMC,
Chennai.

53. • NON–CONTRAST-ENHANCED HELICAL CT
• basis of attenuation values
• success rate - lower for calculi with attenuation
values greater than 1000 Hounsfield units
• Distinguish stone types
• Uric acid from calcium stones
53
Dept of Urology, GRH and KMC,
Chennai.

54. Hounsfield density
• CT attenuation values are
greater than 900–1000 HU
• Skin‐SSD was measured by
averaging the distance
between the center of the
stone
54
Dept of Urology, GRH and KMC,
Chennai.

55. Predictive models of shock‐wave
lithotripsy success
55
Dept of Urology, GRH and KMC,
Chennai.

56. Preoperative considerations
• Antibiotic prophylaxis
• in the absence of urinary tract infections or other
risk factors ,antibiotic prophylaxis prior to SWL is
not indicated
56
Dept of Urology, GRH and KMC,
Chennai.

57. DJ STENTING
• stone‐free rate in those who were stented
preoperatively was 78.1 versus 83% in the
stentless group (P = 0.27).
• The presence of a stent also does not prevent
renal colic, steinstrasse, or additional
procedures
• Current guidelines no longer recommend
routine preoperative stenting
57
Dept of Urology, GRH and KMC,
Chennai.

58. INDICATIONS FOR STENTING
• Large stone burden >1.5 cm
• Obstructed system
• Pyonephrosis
• Poorly visualised stones
58
Dept of Urology, GRH and KMC,
Chennai.

59. INTRA-OPERATIVE DETAILS
• no conclusive data to recommend an optimum
number of shock waves(2000–3000 shock waves)
• 60-90 shocks / min
• Negative pressure phase of a shock wave becomes
dampened at a faster rate(responsible for
cavitation bubbles)
• benefits of a slower shockwave rate are most
notable for stones >10 mm
59
Dept of Urology, GRH and KMC,
Chennai.

60. Pretreatment
• application of low‐energy shock waves to the
targeted renal stone in order to “prime the
kidney” and reduce renal injury( associated
with renal vasoconstriction)
• 300 -500 shock waves applied at 12 kV proven
to significantly reduce the hemorrhagic lesion
size(20 times!)
• 3-4 min pause also decreases hemorrahge
60
Dept of Urology, GRH and KMC,
Chennai.

61. SHOCK WAVE ADMINISTRATION
• Voltage – 12 - 24kV
• Power – 100- 120 Hz
• Number of shock waves – 60-90/min
• Sequence of shock wave delivery
– Step wise power ramping – shock wave intensityis gradually increased
– Two -Step power ramping – (Low to High)
– 100 waves at 18kV followed by 2000 waves at 24kV
61
Dept of Urology, GRH and KMC,
Chennai.

62. Renal Stone
• non staghorn – ideal 6-10mm
• 10-20mm in the absence of other factors
• >20mm not recommended
62
Dept of Urology, GRH and KMC,
Chennai.

63. RENAL ANATOMIC FACTORS
• Ureteropelvic junction obstruction
• Horseshoe kidney
• Ectopic or fusion anomalies
• Calyceal diverticula
63
Dept of Urology, GRH and KMC,
Chennai.

64. Lower pole stones
• Less than 10mm ESWL
• 10-20mm –infundibulopelvic angle more than
70deg, infundibular width more than
4mm,infundibulum length less than 3cm are
favourable.
• More than 20mm PCNL
64
Dept of Urology, GRH and KMC,
Chennai.

65. PUJ obstruction,megaureter, duplicated ureter with
hydronephrosis
Renal scintigraphy should be considered to rule out clinically
significant obstruction.
Three month stone‐free rates for these anatomical variations in
those without obstruction range from 40–55%
CALICEAL DIVERTICULAM
SWL - Stone-free rates are low (0-25%)
May be useful for stones <1 cm in size only if there confirmed,
short and patent diverticular neck which could allow fragment
passage
URINARY DIVERSION
colon conduits is 3–4% and with ileal conduits is 10–20%
SWL monotherapy was found to have an 81.5% success 65
Dept of Urology, GRH and KMC,
Chennai.

66. 66
Dept of Urology, GRH and KMC,
Chennai.

67. CARDIAC PATIENTS
• Gated Lithotripsy(at R wave)
• Pace makers – guarded procedure
• rotating the patient 15–20°
67
Dept of Urology, GRH and KMC,
Chennai.

68. CHILDREN
• SWL for stones >2 cm in size, including staghorn
calculi, can be effective and is acceptable in
children
• Lung protection – Styrofoam paddings
• Low kV and No. of shocks
• Exit site shielding with wet towels –decreased
echymosis
68
Dept of Urology, GRH and KMC,
Chennai.

69. Adjunct therapy after shock‐wave lithotripsy
• to improve stone clearance after SWL, especially for lower
pole stones
• Involve drinking500 ml of water 30 minutes prior to
inversion in a proneTrendelenburg position at 45°
and continuous manual mechanical percussion
over the flank for 10 minute
69
Dept of Urology, GRH and KMC,
Chennai.

70. Medical therapy after shock‐wave
lithotripsy
• α‐adrenergic antagonists
• phyllanthus niruri, a Brazilian plant remedy
which prevents calcium oxalate crystal
• potassium citrate
70
Dept of Urology, GRH and KMC,
Chennai.

71. Follow‐up after SWL
• No consensus on follow‐up imaging after SWL.
• Obtaining plain Xray KUB 1–4 weeks after SWL
• Document SWL failure as being after three
sessions
• Offer endoscopic therapy as the next
treatment option in those who fail a single
session
71
Dept of Urology, GRH and KMC,
Chennai.

72. ESWL FAILURE
• PCNL
• RIRS
• SANDWICH
• OPEN STONE SURGERY
72
Dept of Urology, GRH and KMC,
Chennai.

73. Ureteric stone
• Proximal ureteric stones<1cm ESWL insitu
• SSD cutoff of 11–12 cm
• 70–97% for proximal stones, 58–97.8% for
mid‐ureteral stones, and 54–97.9% for distal
ureteral calculi
• Impacted stones are resistant
73
Dept of Urology, GRH and KMC,
Chennai.

74. ESWL & URETERIC CALCULI
• For fragmentation fluid medium around stone
necessary
• If stones impacted fragmentation may not
occur
• “PUSH & BANG”-success Marginally HIGHER
THAN “in situ ESWL”
74
Dept of Urology, GRH and KMC,
Chennai.

75. • rotating the patient toward the therapy head
increased the success rate significantly for
mid‐ and distal ureteral calculi (from 83.9 to
95% and from 89.1 to 98.0% respectively) and
a significant decrease in number of SWL
sessions for proximal stones
75
Dept of Urology, GRH and KMC,
Chennai.

76. Ureteric stone
76
Dept of Urology, GRH and KMC,
Chennai.

77. • Factor for spontaneous passage of stone
• Width of the stone
• Location
• Width of the stone
• Stones < 4 mm -- rates of spontaneous passage of 80%
• 4 to 6 mm -- 59%
• > 6 mm – 21%
• Location
• Proximal -- 22%
• Middle -- 46%
• Distal ureter -- 71%
• Stones of 5 mm or less, conservative management
77
Dept of Urology, GRH and KMC,
Chennai.

78. Complication of eswl
• Hematuria most common,resolves within a
few hours.
• effect in vessels can be differentiated by
measuring α2‐ macroglobulin enhancement
found immediately after and 1 day following
SWL
• Detoriation of renal function
• Renal colic
78
Dept of Urology, GRH and KMC,
Chennai.

79. Complications
• Steinstrasse
• (Coptcoat’s classification of steinstrasse exists (Type I,
fragments <2 mm in diameter; Type II, leading
fragment 4–5 mm tailed by 2 mm particles; and Type
III,consisting of large fragments),
• Infectious complications: 5.1% in spite of preoperative
sterile urine. MC Escherichia coli
79
Dept of Urology, GRH and KMC,
Chennai.

80. COMPLICATION
Extrarenal Injury
Renal Injury
Acute
Chronic
80
Dept of Urology, GRH and KMC,
Chennai.

81. EXTRARENAL INJURY
• Liver
• skeletal muscle – pain at site of entry
• Gastric and duodenal erosion
• Lung parenchyma
• Acute pancreatitis
• Hematochezia - mucosal damage of the colon
• Myocardial infarctions, cerebral vascular accidents
• cardiac arrhythmia 11and 59% during ungated SWL
• Sperm count
81
Dept of Urology, GRH and KMC,
Chennai.

82. • ACUTE RENAL INJURY
• Structural
• Functional
• Hemorrhage and edema within or around the
kidney
• Intrarenal edema ,Subcapsular hematoma (3% -
12%)
• 6 weeks - 24 months to resolve
82
Dept of Urology, GRH and KMC,
Chennai.

83. 2,000 shocks at 12 (A), 18 (B), 24 (C)
Kv
subcapsular hematona increases
with increasing kV level
83
Dept of Urology, GRH and KMC,
Chennai.

84. Bilateral perinephric hematomas
following bilateral simultaneous
ESWL
84
Dept of Urology, GRH and KMC,
Chennai.

85. • CHRONIC RENAL INJURY
• Structural
• Functional
• chronic renal changes - due to scar formation
• Accelerated rise in systemic blood pressure
• Decrease in renal function
• Increase in the rate of stone recurrence (residual stone
debris)
85
Dept of Urology, GRH and KMC,
Chennai.

86. • CHRONIC HISTOLOGIC CHANGES
• Nephron loss
• Dilated veins
• Diffuse interstitial fibrosis
• Calcium and hemosiderin deposits
• Hyalinized and acellular scars from cortex to
medulla
86
Dept of Urology, GRH and KMC,
Chennai.

87. Steinstrasse ( or Stone Street) – Post
ESWL
87
Dept of Urology, GRH and KMC,
Chennai.

88. Factors influencing renal trauma
• No of shocks 500-8000
• Period of shock wave, decreased period increased
damage
• Kidney size
• Children
• Preexisting RD
• Scarring 2% in adults &7% in children
• Lithotripter output settings such as output energy and
energy flux density, total number of shocks,
• pre‐existing hypertension in older
88
Dept of Urology, GRH and KMC,
Chennai.

89. Damage control
• Use of low power.12-15 kv
• Priming of kidney
• Treat at slow shock wave rate- 1 S W per sec.
• Sedation.
• Number of shock waves to be less
• Maximum session 3-5.interval bt session 10-
14 days.
89
Dept of Urology, GRH and KMC,
Chennai.

90. Dornier HM-3 90
Dept of Urology, GRH and KMC,
Chennai.

91. Siemens Lithostar lithotriptor 91
Dept of Urology, GRH and KMC,
Chennai.

92. LithoDiamond with portable C-arm (modular designs)
92
Dept of Urology, GRH and KMC,
Chennai.

93. • TANDEM-PULSE LITHOTRIPTER
• Lithotripter with auxiliary piezoelectric head to generate a second
shock wave along the same acoustic axis
• Two shock waves are used in rapid succession to drive forceful
collapse of bubbles against stone
• DUAL PULSE LITHOTRIPSY
• Two lithotriptor generate pulses,released simultaneously, both
focused at the same F2 - minimize cavitation
•
93
Dept of Urology, GRH and KMC,
Chennai.

94. Dual pulse lithotripsy.
Coaxially aligned electrohydraulic shock
wave sources with a common F2
94
Dept of Urology, GRH and KMC,
Chennai.

95. 95
Dept of Urology, GRH and KMC,
Chennai.