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U-S.G.R.A-S.G.R.A

ByyD r. K ha ir y EhabD r. K ha ir y Eha

b

PhD O f A nes thes ia & IC

PhD O f A nes thes ia & IC

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ObjectivesObjectives1-1- Advantage of US over the traditional methods

2-2- Scopes of U-S.G.R.A & limitations

3-3- How an image is created from sound waves

4-4- Tissue interaction to Ultrasound5-5-Tissue echogenicity = signature

6-6- Spatial Resolution of US images

7-7- Basic techniques of U-S.G.R.A

8-8- TheART3 of Scanning

9-9-Golden rules during UGRA performance

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Limitations of P. N. S.Limitations of P. N. S.

1-1- PNS guidance is useful only when a motor

response is elicited.2-2- N.S. provides objective but indirect evidence

of nerve location.

3-3- Evidence of proper needle placement (i.e.motor response) disappears after injection of

1-2 mL of local anesthetic.4-4- Motor response achieved at < 0.5 mA does

not guarantee a successful or complete block.

5-5- PNS does not prevent intravascular,

intraneural or pleural puncture.

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Limitations Of MultipleLimitations Of Multiple

Radiologic ModalitiesRadiologic Modalities

Costs

Requirement of prohibitive space

No visualization of nerve structures

Static images i.e. no real time positionof needle and injections

The need for contrast dye

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USUS & Regional Anesthesia& Regional Anesthesia

The key for successful R.A. is toensure optimal distribution of L.A.

around nerve structures.

This goal is most effectively

achieved under sonographicvisualization.

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Advantages of U-S.G.R.A.Advantages of U-S.G.R.A.1-1- Direct visualization of nerves

2-2- Direct visualization of anatomicalstructures blood vessels, muscles,

bones, tendons facilitating identificationof nerves

3-3- Direct visualization of the spread of L.A.during injection, with possibility of

repositioning the needle in cases of mal-

distribution of L.A.

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4-4- Making more blocks feasible e.g.

sensory nerves, neuropathic nerves

5-5-Increases safety by avoidance of side-effects e.g. inadvertent intraneuronal,

IV injection of local anesthetic

6-6- Avoidance of painful muscle

contractions during nerve stimulation

Advantages of U-S.G.R.A.Advantages of U-S.G.R.A.

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Advantages of U-S.G.R.A.Advantages of U-S.G.R.A.

7-7-Reduction of the dose of localanesthetic

8-8- Faster onset time

9-9- Longer duration of blocks

10-10- Improved quality of block

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Other AdvantagesOther Advantages

of U-S.G.R.A.of U-S.G.R.A.Noninvasive.

No radiation exposure.

More affordable and portable.

Requires little preparation for

immediate use.

Easy taught and learned.

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Indications And Scope ofIndications And Scope of

PracticePracticeUS is used for anatomic evaluation and

to facilitate the performance of both

neuraxialneuraxial, peripheral nerve blocksperipheral nerve blocks,muscular-skeletal injection,muscular-skeletal injection, CVPCVP, and

ALAL insertion.

It is particularly useful in patients withobscure anatomic landmarks,coagulopathy, neural pathology, and

severe extremity trauma.

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ContraindicationsContraindications

There are no known absolute

contraindications to the use of US.

With respect to safety, F.D.A has stated,

Even though there are no known risks,

ultrasound energy heats the tissuesand may have other biologic effects.

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How an Image isHow an Image is

Created from Sound waves?Created from Sound waves?

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PhysicsPhysicsUltrasound is a mechanical vibrating energy

travels longitudinally though molecules ofsubstance producing an alternating compression

high pressure and rarefaction low pressure.

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Four Main Parts of SoundFour Main Parts of Sound

WaveWave

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Generation of US WaveGeneration of US Wave

Piezoelectric effectPiezoelectric effect is used to convert the energy of an electric field

applied to an array of piezoelectric crystals

into mechanical vibration that produce sound

waves.

The sum of wavessum of waves produced by all crystalsall crystals

forms the US beamUS beam.

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Character of US WaveCharacter of US Wave Waves are generated inpulsespulses i.e.

intermittent trains of pressure waves, eachpulse consists of 2 or 3 sound cycles of thesame frequency.

Pulse length PLPulse length PListhe distance traveledper pulse

Pulse RepetitionPulse RepetitionFrequency PRFFrequency PRFisthe rate of pulses emitted by the transducer

number of pulses per unit time.

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Phases of USPhases of US

Image GenerationImage Generation 1- Sound generator = Transmitter

##Pulsar: applies high amplitude voltage toenergize the piezoelectric crystals

##Transducer: converts electrical energy tomechanical US energy

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2-Waiting2-WaitingDuring which tissue interface occur i.e.

Absorption,Reflection, &

Refraction.

3-Receiving3-ReceivingReceiverReceiver = detects and amplifies weak signals.

The same transducer converts mechanical US

energy to electrical

energy

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4-Display4-DisplayDisplays ultrasound signals in a variety ofmodes

1- Amplitude AA mode 2- BBrightness BB mode

3- MMotion MMmode

BB mode is most commonly used formode is most commonly used for

ultrasound guided regional anesthesiaultrasound guided regional anesthesia

5- Memory5- Memory

Store video display

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USUS-Tissue Interaction-Tissue Interaction

The amplitude of the original US beambecomes attenuated as the depth ofpenetration increases.

Attenuation energy loss depends on: Tissue interfaceTissue interface1-1-Absorption

2-2- Reflection & Refraction

AAt interfacet interfacess

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1- Absorption1- Absorption Represent 80% of sound wave

attenuation It is determined byIt is determined by1-1-Distance waves have to travel

A direct relation shipA direct relation ship2-2- Specific tissue type

Attenuation coefficientAttenuation coefficient A measurement of sound wave attenuation

in decibels per centimeter of specific tissue. Lowest in water & highest in boneLowest in water & highest in bone

-3- The selected fre uenc of US

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Frequency, & AttenuationFrequency, & Attenuation

The degree of attenuation varies directly withthe frequency of the ultrasound wave andthe distance traveled.

Frequency = Attenuation; Attenuation=

Penetration

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2- Reflection2- Reflection

Attenuation results from reflection of USwave.

The extent of reflection is determined byThe extent of reflection is determined by

Acoustic impedanceAcoustic impedanceThe angle of the incidenceThe angle of the incidence

The reflecting surfaceThe reflecting surfaceThe speed of sound in different tissuesThe speed of sound in different tissues

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1- Acoustic Impedance1- Acoustic Impedance

The resistance of a tissue to the passage of US.

Impedance mismatch between two tissues atthe interface Reflection.

It is highest in bone, & lowest in airIt is highest in bone, & lowest in air

Thats whyThats why Sufficient conducting gel should be applied

on the transducer surface Otherwise much ofthe ultrasound waves will be reflected limiting

tissue penetration.

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2- The Angle of the Incidence2- The Angle of the Incidence

US waves hitting a smoothsmooth interface at rightangle 9090 results in a perpendicularreflection.

Angle of reflectionAngle of reflection

If the angle of incidence is < 90< 90, wavesare deflected with equal angle in the oppositedirection.

ThatThats whys why

it is difficult toit is difficult tovisualize a needlevisualize a needle

inserted at a steepinserted at a steep

angle >angle >

4545

to the skinto the skin

surface.surface.

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3- Reflecting Surfaces3- Reflecting Surfaces

SPECULARSPECULARREFLECTIONREFLECTION

SCATTERING=SCATTERING=diffuse reflectiondiffuse reflection

Smooth interfaces

e.g., sheaths, BV,&Blocking needles

USUS wavelengthwavelengthmust be

reflective structuree.g., RBCs.

Determines types of waves reflection

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RefractionRefractionThe change in the direction of US beam when

the speeds of sound are different on eachside of the tissue interface

Tissues like bones>>

fatcause considerablerefraction and imagedistortion.

This contributesThis contributestoto some of thedifficulties encounteredin obese patients.

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TISSUE EchogenicityTISSUE EchogenicityEchogenicityEchogenicityis the degree of brightness of

dots on the display that combine to formsthe final image.

It is determined byIt is determined by the amplitude of echo

returns to the transducer.

HyperechoicHyperechoicis brightdots result from astrong specular reflections.

HypoechoicHypoechoicisgreydots result fromWeaker diffuse reflections.

AnechoicAnechoic is darkdots result from no

reflection.

TISSUETISSUE US IMAGE FOR R AUS IMAGE FOR R A Signature

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TISSUETISSUE US IMAGE FOR R.A.US IMAGE FOR R.A. Signature

Veins anechoicanechoic (compressible)

rteries anechoicanechoic (pulsatile)

Fat hypoechoichypoechoic with irregular hyperechoic lines

Muscles heterogeneousheterogeneous (mixture of hyperechoic lines

within a hypoechoic tissue background)

Tendons predominantly hyperechoicpredominantly hyperechoic technical artifact(hypoechoic)

Bone ++ hyperechoic++ hyperechoic lines with a hypoechoichypoechoic shadow

Nerves hyperechoic / hypoechoichyperechoic / hypoechoic technical artifact(hypoechoic)

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Tissue SignatureTissue Signature

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- ArteryArteryAA roundanechoicanechoic- VeinVeinVV ovalanechoicanechoic- Vein is collapsible while an artery is not.

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FatFat has a hypoechoichypoechoic background With hyperechoichyperechoic irregular lines

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MuscleMuscle hypoechoichypoechoic background

with hyperhyperechoicechoic facial sheath lines

BoneBone hyperhyperechoicechoic outline underneath a hypoechoichypoechoic bony shadow Due to a lack of beam penetration

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NerveNerveis oval TendonTendon has an irregular shape merges into

a muscle proximally

A cross section of the forearm

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Longitudinal section of a NerveNerve shows

continuous hypoechoichypoechoic = fasciclefascicle

HyperechoicHyperechoic = perineural connectiveperineural connective

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Longitudinal section of a

TendonTendonlooks like alooks like a NerveNerve

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NervesNervesare generally hypoechoichypoechoic in the

interscalene and supraclavicular regions

interscalene regioninterscalene region

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NervesNervesbelow the clavicle and L.L.below the clavicle and L.L. arepredominantly hyperechoichyperechoic and have a honey comb

appearance.

The degree ofhyperhyperechogenicityechogenicity reflects thethe

amount ofamount ofconnective tissueconnective tissue within the nerve.within the nerve.

S ti lS ti l

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SpatialSpatial

Resolution of US ImageResolution of US Image ResolutionResolution is the ability of the US

machine to distinguish two structures that areclose together as separate. It depends onIt depends on

1-1- Machine factorsMachine factors # :l t r a s o u n d P r o be s &Determine Lateral Axial Resolutions # :o m p u t e r P r oc e s s i n g ,Adjusted to improve Temporal Resolution

while creating images from the receivedelectrical signals

2-2-The ARTThe ART33 of Scanningof Scanning

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Axial ResolutionAxial Resolution

The ability to distinguish two structures that liealong the axis i.e. paralleli.e. parallel of the ultrasoundbeam as separate and distinct.

Axial resolution is determined ByAxial resolution is determined By

The pulse length

A high frequency wave has shorter pulselength better axial resolution than a lowfrequency wave.

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Lateral ResolutionLateral ResolutionRefers to resolution of objects lying side by

side i.e., perpendicular to the beam axisi.e., perpendicular to the beam axis.

Determined By Beam widthBeam width

The narrower the beam the betterThe narrower the beam the better

ResolutionResolution

US frequency narrowing beam width

improving lateral resolution

But it is limited by tissue attenuation

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Processingrocessing--

Adjusting Focal ZoneAdjusting Focal Zone

Narrowest beam widthNarrowest beam width is at the focal zonefocal zoneafter which the beamdiverges as itgoes deeperinto the field

Thats whyThats whyAdjustment offocal zonefocal zone gives the bestbest

possible lateral resolutionpossible lateral resolution without the need to increase frequencywithout the need to increase frequency

22 I D thI D th

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2-2- Image DepthImage Depth Image depth should be just below theImage depth should be just below the

scanned targetscanned target Why?

Decreases the size of the imageproduced by the device increases itssweep speed, hence it increases thesweep speed, hence it increases the

US Frame Rate ,US Frame Rate , andand

Temporal ResolutionTemporal Resolution

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3- Adjusting Gain3- Adjusting Gain

Increasing gainIncreasing gain amplifies onlyonly the intensityof the returning echo signal, resulting in:

## IncreasesIncreases image brightness ## IncreasesIncreases background noise

Time gain compensationTime gain compensationTGC,Selectively amplifies the weaker signalsreturning from deeper structures resulting in:resulting in: ## IncreasesIncreases image brightness

## ReducesReduces background noise

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Review of US TechnologyReview of US TechnologyImage quality depends on ProbeProbe technology and Computer ProcessorComputer Processor

Signal intensity depends on the proportion ofreflected wavesreflected waves returning to

the transducer

Nerve appears hyper or hypoechoic dependingon density of its connective tissuedensity of its connective tissue

High frequencyHigh frequency improves ResolutionResolution but,but, increases AttenuationAttenuation

B i T h i fB i T h i f

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Basic Techniques ofBasic Techniques of

U-s. G. R AU-s. G. R A

F S ff U S G R A

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Four StepsFour Stepsof U-S.G.R.A.of U-S.G.R.A.

1-1- Checking for transducer orientation2-2- Choosing one of two imaging views

##ShortShort axis view ##LongLong axis view

3-3- Choosing needle approach technique

##InIn plane ##OutOut of plane

4-4- Optimization of image during scanning

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Orientation of The PropOrientation of The Prop1.1. Conventional methodConventional method Transducer markerTransducer marker

A-A-During transverse scan

Transducer marker is oriented to the R sideR side

of the examined subject.

B-B-During longitudinal scan

It is oriented in the cephalic directioncephalic direction.

2.2. Touching the transducer surface on one sideafter gel application will immediately show

transducer orientation.

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3.3. Moving the transducer to one sideMoving the transducer to one side of thebodye.g., medially

The side of the screen one sees more

anatomical structures is the medial side.

I i ViI i Vi

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Imaging ViewsImaging ViewsLong Axis ViewLong Axis View or Longitudinal ViewLongitudinal View

--Rarely used except for IV, & ALinsertion

Short Axis ViewShort Axis View or Transverse ViewTransverse View -- Most commonly used -- Relatively easy -- Better resolution of facial barriers

(CT) surrounding the nerves -- Dynamic assessment of

circumferential L.A. spread -- Workable image even with slight

Where is TheWhere is The

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Where is TheWhere is The

Needle Coming From?Needle Coming From?

1- Out of Plane Technique1- Out of Plane Technique

Inserting the needleneedle so that it crosses

the plane of imaging near the targetnear the target.

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Advantages ofAdvantages of

Out of Plane TechniqueOut of Plane Technique

1-1- Shorter needle insertion paths

2-2-Less patient discomfort

3-3- Easier to perform

f

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Disadvantages ofDisadvantages of

Out of Plane TechniqueOut of Plane Technique

1-1- Unable to visualize the needle shaft

2-2- Difficulty in finding the needle tip, as

it crosses the US beam

2 l h i

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NeedleNeedle is inserted within the plane of imaging to

visualize the entire shaft andvisualize the entire shaft and

2- In Plane Technique2- In Plane Technique


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In Plane TechniqueIn Plane Technique

1-1- Ability to track the Needle shaft &

tip

2-2- Seems to be more safe

fDi d f

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Disadvantages ofDisadvantages of

In Plane TechniqueIn Plane Technique

1-1- More time consuming

2-2- More difficult to perform 3-3- Can be more painful secondary to

longer insertion paths

Th ARTThe ART33 f S iof Scanning

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The ARTThe ART33 of Scanningof Scanning

RRotationotation

AAlignmentlignment

TTiltingilting

1- Alignment1- Alignment

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1- Alignment1- Alignment

Sliding the transducer longitudinally along the Short AxisShort Axis to

trace a course of a target .nerves or a needle

2 R t ti2 Rotation

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2- Rotation2- Rotation

Clockwise/counter- clockwise

movement of theprop

Used to alignprop,prop,

needle, & nerveneedle, & nerve in

one plane.

Helpful during LongLong

Axis scanAxis scanof the

nerve and in plane

A Sonogram in the PoplitealRegion show Visualization of both

needle & sciatic in the Long Axis

3 Tilting3- Tilting

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3- Tilting3- Tilting Angling movement of prop to optimize the

angle of incidence 90

At 75 the nerve less clearly visible

90 the nerve is clearly visible

Golden RulesGolden Rules

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DuringDuring

U-S.G.R.A. PerformanceU-S.G.R.A. Performance

G ld R l D iG ld R l D i

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Golden Rules DuringGolden Rules During

U-S.G.R.A. PerformanceU-S.G.R.A. Performance1-1- Visualize key landmark structure including blood vessels, muscles, fascia,

and bone.

2.2. Identify the nerves or plexus on short

axis imaging.

3.3. Confirm normal anatomy and recognize

anatomic variationss.

G ld R l D iGolde R le D i

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U-S.G.R.A. PerformanceU-S.G.R.A. Performance4.4. Plan for a needle approach that avoids

unnecessary tissue trauma.

5.5. Maintain an aseptic technique with

respect to the ultrasound equipment.

6.6. Follow the needle under real-time

visualization as it advances toward the

target.


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U-S.G.R.A. PerformanceU-S.G.R.A. Performance7.7. Consider nerve locator as a secondaryconfirmation technique.

8.8. Use small volume of a test solution toconfirm the correct needle tip position.

9.9. Readjustment of the needle if anundesired pattern of L.A. spread isvisualized.

G ld R l D iGolden Rules During

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U-S.G.R.A. PerformanceU-S.G.R.A. Performance10.10. Maintain traditional safetytraditional safety guidelines

## Patient response

## Standard monitoring

## Resuscitation equipment

## Emergency drugs

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USGRA-7

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