Dr. Amr Abdulfatah Sayed (M.D.) Associate prof. of Anesthesia,
Chronic Pain Management Ain Shams Univ., Cairo, EGYPT Oct.
2012
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NO clicks No pops No paresthesia No trans-arterial Under vision
in real time How L.A. behaves How catheter lodge Reinjection with
inconsistent block
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Mechanical sound energy. Sinusoidal. Pulse longitudinal wave
alternating compression (high pressure) & rarefaction (low
pressure) P = pressure T = wave length F= frequency distance one
peak to other peak is a wavelength one peak to other peak is a
wavelength
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electric field is applied to a piezoelectric crystals.
mechanical distortion of the crystals sound waves (i.e. mechanical
energy)
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Elect. impulse Mech. sound Elect. image
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U/S beam travels through different tissues attenuation
Subjected to attenuation (Energy Loss). 1) absorption. 2)
reflection. 3) scattering. Factors affecting attenuation :
Frequency ( high high atten ) ( low low atten) Travel distance
Tissue nature
Lateral Resolution ( side-by-side) : to visualize two
structures @ same plane & perpendicular to U/S beam improved by
increasing F or transducer diameter Axial Resolution : ( above the
other) : @ different tissue depths Improved by higher
frequencies
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Lat. Axial
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The Ultrasound Transducer Source of Energy and Image Energy
progressively degraded (attenuate) as it enters deeper tissues
lateral & axial resolution improved with higher frequency
transducers, decrease with increasing tissue depth
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Structures typically seen as hyperechoic or echogenic include
bone, tendons, pleura, and nerves below the clavicles. In contrast,
blood, fluids, and nerves above the clavicles are hypoechoic.
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Generally speaking, a high frequency wave is subjected to high
attenuation thus limiting tissue penetration low frequency wave is
associated with low tissue attenuation and deep tissue
penetration.
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Frequency is expressed in MHz number of compressions peaks
/sec. ( Pr. Peaks ) High frequency = less tissue penetration = high
attenuation) Low frequency = high tissue penetration.
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receiver amplification is called the Gain. Gain increases
overall brightness of the entire image, including the background
noise. (TGC) selectively amplify the weak returning (attenuated)
signals from deeper structures. Gain TGC
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Tissue impedance resistance of a tissue to US passage Strong
wave reflection = hyperechoic (white) Weak reflection= hypoechoic
(greyish) No reflection = anechoic. (black) Body Tissue Acoustic
Impedance (10 6 Rayls) Air0.0004 Lung0.18 Fat1.34 Liver1.65
Blood1.65 Kidney1.63 Muscle1.71 Bone7.8
Fat hypoechoic with irregular hyperechoic lines Muscles
heterogeneous (mixture of hyperechoic lines within a hypoechoic
tissue background)
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Bone : High tissue impedance Strong reflection ++ hyperechoic
lines with a hypoechoic shadow underneath
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fascicular or honeycomb appearance
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Reflection is high for air Air has extremely low acoustic
impedance (0.0004) acoustic coupling medium on the transducer
surface to eliminate any air pockets Otherwise ultrasound waves
will be reflected limiting tissue penetration. large dropout
artifact.
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hyperechoic region, deep to a fluid filled structure (e.g., a
vessel beam passes from area of low attenuation to higher
attenuation coefficient.
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twice Reverberation artifacts U/S/waves striking a surface
twice that is close to perpendicular commonly seen with highly
attenuating wide-bore needles
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deep to hyperechoic bone outline is a beam attenuation
Ultrasound beams subjected to attenuation by bone, penetration is
severely impeded.
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Linear array probe High frequency( > 6MHz) Superficial
structures Depth max. 6 cm High clarity Curved probe Low frequency
(2-5 MHz) Deep structures > 6cm Less resolution Hokey stick
25mm
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Transducer marker
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Needle probe orientation Handling of probe resting hand on pt.
body Non dominant hand More steep angle of needle = difficult
visualization IN PLANE (IP)OUT OF PLANE (OOP)
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Large bore needles (e.g. 17 G) Better visualization easier to
direct. Preferred for deep blocks (e.g. infraclavicular block,
sciatic ) when needle insertion is steep (> 45 degrees) Smaller
bore needles (e.g. 22 G) easily visualized for more superficial
blocks e.g., the axillary block, when the angle of needle insertion
is shallow.
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A ( Alignment ) R ( Rotation) T ( Tilting)
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Proper handling the transducer and the needle, to view the
screen, and to position the patient are essential for block success
and to avoid operator fatigue and body injury.
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PROPER BODY POSITION IMPROPER BODY POSITION
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IMPROPER OPERATOR AND SCREEN ORIENTATION PROPER OPERATOR AND
SCREEN ORIENTATION
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IMPROPER HAND AND ARM POSITIONS PROPER HAND AND ARM
POSITION
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Transverse View (short axis view) for nerves e.g. Brachial
plexus
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Aim to surround the neural structure Doughnut sign. Saline of
D5% ( if PNS) Prior to L.A Aspirate 1 st
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doughnut sign. Doughnut sign. F.A
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Glut. max Sc. N.
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PROPONENTSCRITICS improve success rates simplify the technical
challenges decrease performance times reduce complications lack of
controlled trials High expense equivocal nature of images Requires
sustained training.
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Adults USGRA can be performed in children Plan @ pre-op visit
Explain for partents ( legal guardian ) Ped. USGRA performed under
anesthetized light sedation ( esp. > 8 yrs, diff. airway,MH).
EMLA 1 hrs in advance f Small muscle bulk = high f probe (13-6 MHz,
hockey- stick, 26-mm footprint)
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Insulated needle Epidural 22G for catheter ( long term post
op). In-plane > out off plane Calculate full dose ( volume
0.30.5 mL/kg ) < 5 yrs Bupi. 0.25 %, Ropi. 0.2%, Lido 1% 5 yrs
Bupi. 0.375 %, Ropi. 0.5% +epi. ( Allison Ross et al., A & A
July 2000 vol. 91 no. 1 16-26)
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Any Questions ?
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Interscalene Supraclavicular Infraclavicular Axillary Median N.
Ulnar N. Radial N. 0.25 -0.5ml /kg 0.25% bupivacaine, 1% lidocaine,
0.25% ropivacaine
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Most cranial approach Not popular ( Phrenic N.) Indication :
shoulder, upper arm, lateral clavicle. Scanning : Medial to lateral
survey Trace Back Method Injectate Perfect Block = 0.15-0.3ml /kg
front, in the sheath & behind
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Colour Doppler : to identify vertebral vs & branches of
transverse cervical artery below C6 SCM Sc. a Sc. m medial
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Clinical tips The usual volume of L.A. 0.3-0.5ml/kg. (Corner
Pocket ) above the 1 st rib, next to subclavian a. to anesthetize
the lower trunk. In plane approach is a must All U.L ???? Shoulder
surgery 2/3 L.A. @ Corner
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Groove Coracoid lateral Pectoralis Maj medial Calvicle superior
Better catheter insertion
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Local anesthetic injected posterior to the axillary artery
resulting in a U shape spread around the artery is associated with
complete blockade of the arm, forearm and hand.
superficial to the Ilio-Psoas Muscle (IPM) Base touching CFA,
extending lateral to it. C
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Surgery on femur, knee
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L4 L3 Dermatomes and osteotomes of the lumbosacral plexus are
illustrated. (Courtesy of Mayo Foundation.) The American Society of
Regional Anesthesia and Pain Medicine. 2005
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6-8 cm Pect
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Plus femoral : whole LL block Single for ankle & foot
surgery
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TAP Thoracic Paravetebral Block Psoas Block
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TechniqueDose (mL/kg)Usual Volume (mL) Brachial plexus
blocks0.15-0.3 mL/kg10 mL Femoral nerve block0.2-0.3 mL/kg10 mL
Sciatic nerve0.3 -0.5 mL/kg10-15 ml Psoas (lumbar block )0.3 -0.5
mL/kg10-15 ml (David M. Polaner et al. Regional anesthesia, The
Practice of PediatricAnesthesia. 4 th ed. 2009) Suggested Dosing
for Local Anesthetic Volumes for Common Peripheral Nerve Blocks
(David M. Polaner et al. Regional anesthesia, The Practice of
PediatricAnesthesia. 4 th ed. 2009)
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Real time L.A. behaves Less L.A. Cath. Fixation Less vasc.
& pleural insults L.A. Re-deposition @ insufficient block All
benefits of R.As