Ultrasound and Ultrasound and Regional Regional

AnesthesiaAnesthesiaJim Sparrow, MDJim Sparrow, MD

UAB Anesthesia Grand UAB Anesthesia Grand RoundsRounds

February 9, 2009February 9, 2009

Topics We Will CoverTopics We Will Cover

Basic ScienceBasic Science: Ultrasound : Ultrasound Technology and TerminologyTechnology and Terminology

Clinical TechniquesClinical Techniques: Generalized : Generalized Ultrasound Techniques used in Ultrasound Techniques used in Regional AnesthesiaRegional Anesthesia

Literature ReviewLiterature Review: Ultrasound : Ultrasound Guidance Outcome DataGuidance Outcome Data

DiscussionDiscussion: Is Ultrasound the : Is Ultrasound the Future or Just a Fad Future or Just a Fad

Why This is ImportantWhy This is Important

New technology requires thorough New technology requires thorough investigation to determine safety, investigation to determine safety, efficacy, reliability and cost efficacy, reliability and cost effectiveness.effectiveness.

Ultrasound is already here and Ultrasound is already here and certain “experts” are proclaiming certain “experts” are proclaiming that its use should be standard of that its use should be standard of care.care.

Introduction to the Introduction to the Basic Physics and Basic Physics and

Terminology of Terminology of UltrasoundUltrasound

Ultrasound WavesUltrasound Waves Form of Acoustic EnergyForm of Acoustic Energy Generated by Piezoelectric Crystals Generated by Piezoelectric Crystals

in Specialized Transducer Probesin Specialized Transducer Probes Curved ArrayCurved Array Linear ArrayLinear Array

Specific Frequency RangesSpecific Frequency Ranges

Ultrasound Wave Ultrasound Wave PropagationPropagation

Longitudinally PropagatedLongitudinally Propagated Series of BriefSeries of Brief

Compressions (High Pressure)Compressions (High Pressure) Rarefactions (Low Pressure)Rarefactions (Low Pressure)

Velocity of Propagation Velocity of Propagation Depends on the MediumDepends on the Medium

Acoustic VelocityAcoustic Velocity

Propagation Velocity of a Sound WavePropagation Velocity of a Sound Wave Is Constant in the Human BodyIs Constant in the Human Body In Humans = 1540 meters/secondIn Humans = 1540 meters/second Represented by the EquationRepresented by the Equation

C = C = ƒ*ƒ*λλc= 1540 m/sc= 1540 m/sƒ= frequencyƒ= frequencyλλ= wavelength= wavelength

How is an Image How is an Image Created from Created from Soundwaves?Soundwaves?

Image CreationImage Creation Requires Return of Requires Return of

Soundwave to Probe Soundwave to Probe ((Like a BoomerangLike a Boomerang))

Probes rapidly cycle Probes rapidly cycle from Transmission to from Transmission to ReceptionReception

Cycles can be Cycles can be 7000/second7000/second

Returning waves are Returning waves are converted to Electrical converted to Electrical ImpulsesImpulses

Computer Processing Computer Processing creates a 2-creates a 2-Dimensional ImageDimensional Image

Two Determinates of Two Determinates of Ultrasound Image QualityUltrasound Image Quality

Ultrasound Probes: Ultrasound Probes: Transmits and Receives Ultrasound Transmits and Receives Ultrasound

WavesWaves

Computer Processing:Computer Processing: Creates Computer Image from Electrical Creates Computer Image from Electrical

Signals Received from the ProbeSignals Received from the Probe

Signal IntensitySignal Intensity

Determined by degree of reflected Determined by degree of reflected waves returning to the transducerwaves returning to the transducer

Larger intensities = Strongly reflected Larger intensities = Strongly reflected = Hyperechoic image (Whiter)= Hyperechoic image (Whiter)

Weaker intensities = Weakly Reflected Weaker intensities = Weakly Reflected = Hypoechoic (Darker)= Hypoechoic (Darker)

Image: (1) Sites et al

Ultrasound Wave Ultrasound Wave Interaction with TissuesInteraction with Tissues

ReflectionReflection SPECULARSPECULAR (large (large

smooth objects smooth objects like a needle) (d)like a needle) (d)

SCATTERINGSCATTERING (most (most neural images)neural images) (a) (a)

Refraction (c)Refraction (c) TransmissionTransmission

(b)(b)

Reflection of Ultrasound Reflection of Ultrasound WavesWaves

Proportional to the difference in Proportional to the difference in acoustic impedanceacoustic impedance between adjacent between adjacent tissuestissues

Greater difference = better distinction Greater difference = better distinction = better = better resolutionresolution

Explains the varying appearances of Explains the varying appearances of nervous tissue on U/S imagingnervous tissue on U/S imaging

Interscalene vs PoplitealInterscalene vs Popliteal

Hyper vs. Hypoechoic Hyper vs. Hypoechoic NervesNerves

RefractionRefraction Occurs at tissue interfaces (unreflected)Occurs at tissue interfaces (unreflected) Refraction can diminish image qualityRefraction can diminish image quality Increases with angle of incidenceIncreases with angle of incidence

Optimal angle of incidence is 90°Optimal angle of incidence is 90° Perpendicular probe minimizes effectPerpendicular probe minimizes effect

Optimal Image Resolution Optimal Image Resolution is a Balanceis a Balance

AttenuationAttenuation

Progressive loss of energy with signal Progressive loss of energy with signal propagationpropagation

Results in progressive decrease in returning Results in progressive decrease in returning signalsignal

Major source is conversion of acoustic energy to Major source is conversion of acoustic energy to heatheat

Loss of signal is directly related to depthLoss of signal is directly related to depth Attenuation is medium dependentAttenuation is medium dependent Represented by the Attenuation Co-efficientRepresented by the Attenuation Co-efficient

Bone>>Air>>>Muscle>Brain>Fat>Blood>>>WaterBone>>Air>>>Muscle>Brain>Fat>Blood>>>Water

   

Body Tissue

Attenuation Coefficient

(dB/cm at 1MHz)

Water 0.002

Blood 0.18

Fat 0.63

Liver 0.5-0.94

Kidney 1.0

Muscle 1.3-3.3

Bone 5.0

   

Body Tissue Acoustic Impedance

(106 Rayls)

Air 0.0004

Lung 0.18

Fat 1.34

Liver 1.65

Blood 1.65

Kidney 1.63

Muscle 1.71

Bone 7.8

Attenuation and Attenuation and FrequencyFrequency

Higher Frequency results in greater Higher Frequency results in greater attenuationattenuation

Overcoming Loss of Signal Overcoming Loss of Signal from Attenuationfrom Attenuation

Artificial Enhancement Artificial Enhancement (Adjusting Gain)(Adjusting Gain)

Time Gain Time Gain CompensationCompensation

Adjusts gain Adjusts gain independently at independently at specified depth specified depth intervalsintervals

Most modern U/S Most modern U/S machines do this machines do this automatically automatically (autogain)(autogain)

Choosing lower Choosing lower frequencies for deeper frequencies for deeper tissues (posterior tissues (posterior sciatic)sciatic)

The Holy Grail: Better The Holy Grail: Better ResolutionResolution

Resolution refers to the ability to Resolution refers to the ability to distinguish one object from anotherdistinguish one object from another

Three important typesThree important typesAxialAxialLateralLateralTemporalTemporal

In General: Higher Frequency In General: Higher Frequency Ultrasound Yields Better Ultrasound Yields Better ResolutionResolution

Axial ResolutionAxial Resolution

Separating two Separating two structures at structures at Different DepthsDifferent Depths

Equal to ½ of Equal to ½ of pulse lengthpulse length Distance between Distance between

objects must be objects must be greater the ½ pulse greater the ½ pulse length to be seen as length to be seen as separateseparate

Lateral ResolutionLateral Resolution

Separating two Separating two structures beside structures beside one anotherone another

Always worse Always worse than axial than axial resolutionresolution

Close U/S beams Close U/S beams improve lateral improve lateral resolutionresolution

Temporal ResolutionTemporal Resolution Directly related to U/S Directly related to U/S

Frame Rate (FR)Frame Rate (FR) FR is the speed with FR is the speed with

which an imaging which an imaging device produces device produces unique consecutive unique consecutive imagesimages

FR is limited by sweep FR is limited by sweep speedspeed

Sweep speed is limited Sweep speed is limited by image depthby image depth

Image depth should be Image depth should be just below targetjust below target

Review of Ultrasound Review of Ultrasound TechnologyTechnology

Image quality depends on probe technology and Image quality depends on probe technology and computer processorcomputer processor

Signal intensity is dependent on the proportion of Signal intensity is dependent on the proportion of reflected waves returning to the transducerreflected waves returning to the transducer

Nerves appears hyper or hypoechoic depending on Nerves appears hyper or hypoechoic depending on surrounding tissuesurrounding tissue

Resolution is Resolution is improvedimproved with high frequency with high frequency ultrasound but Attenuation is ultrasound but Attenuation is greatergreater for higher for higher frequency ultrasound: Must find the right balance frequency ultrasound: Must find the right balance for image optimizationfor image optimization

Basic Techniques of Basic Techniques of Ultrasound Ultrasound Guidance in Guidance in

Regional AnesthesiaRegional Anesthesia

All Ultrasound Guided All Ultrasound Guided Blocks Involve Three Blocks Involve Three

StepsSteps22:: Choosing One of Two Imaging ViewsChoosing One of Two Imaging Views

Short Axis ViewShort Axis View Long Axis ViewLong Axis View

Scanning the Nerve Track for Image Scanning the Nerve Track for Image OptimizationOptimization

Choosing a Needle Approach Choosing a Needle Approach TechniqueTechnique In PlaneIn Plane Out of PlaneOut of Plane

Imaging Plane OptionsImaging Plane Options Long Axis View or Longitudinal ViewLong Axis View or Longitudinal View

Rarely UsedRarely Used Short Axis View or Transverse ViewShort Axis View or Transverse View

Most Commonly UsedMost Commonly Used Relatively EasyRelatively Easy Better Resolution of Fascial Barriers that Better Resolution of Fascial Barriers that

Surrond NervesSurrond Nerves Dynamic Assessment of Circumferential Local Dynamic Assessment of Circumferential Local

Anesthetic SpreadAnesthetic Spread Workable Image Even with Slight Movement of Workable Image Even with Slight Movement of

Transducer ProbeTransducer Probe

The ARTThe ART33 of Scanning of Scanning AAlignmentlignment

Sliding Movement of Trandsducer Along the Course of the Sliding Movement of Trandsducer Along the Course of the Nerve Lengthwise (Used in Short Axis View)Nerve Lengthwise (Used in Short Axis View)

RRotationotationClockwise/Counterclockwise Transducer Movement Clockwise/Counterclockwise Transducer Movement

(Particularly important when attempting a long axis view)(Particularly important when attempting a long axis view) TTiltingilting

Angling Movement of Transducer to Optimize the Angle of Angling Movement of Transducer to Optimize the Angle of Incidence (90º)Incidence (90º)

Where is The Needle Where is The Needle Coming From?Coming From?

Out of Plane TechniqueOut of Plane TechniqueInserting the needle so that it crosses the Inserting the needle so that it crosses the

plane of imaging near the target.plane of imaging near the target.

In Plane TechniqueIn Plane TechniqueInserted within the plane of imaging to Inserted within the plane of imaging to

visualize the entire shaft and tip.visualize the entire shaft and tip.

Out of Plane ApproachOut of Plane Approach

In Plane ApproachIn Plane Approach

AdvantagesAdvantages

Out of Plane TechniqueOut of Plane Technique Shorter Needle Insertion PathsShorter Needle Insertion Paths Less Patient DiscomfortLess Patient Discomfort Easier to PerformEasier to Perform

In Plane TechniqueIn Plane Technique Ability to Track the Needle TipAbility to Track the Needle Tip Theoretically SaferTheoretically Safer

DisadvantagesDisadvantages Out of Plane TechniqueOut of Plane Technique

Unable to accurately track needle tipUnable to accurately track needle tip Difficulty finding the echogenic “dot” as the Difficulty finding the echogenic “dot” as the

needle crosses the US beamneedle crosses the US beam In Plane TechniqueIn Plane Technique

More Time ConsumingMore Time Consuming More difficult to performMore difficult to perform False security when partial needle lineups give False security when partial needle lineups give

appearance of a needle tipappearance of a needle tip Can be more painful secondary to longer Can be more painful secondary to longer

insertion pathsinsertion paths

(Gray 2007)

Reviewing the Basic Reviewing the Basic Ultrasound TechniquesUltrasound Techniques

Literature Review: Literature Review: Ultrasound Use in Ultrasound Use in

Regional AnesthesiaRegional Anesthesia

Just In Time!Just In Time!

Liu et al

MethodsMethods

Inclusion CriteriaInclusion Criteria RCT comparing ultrasound guided RCT comparing ultrasound guided

regional anesthesia with an alternative regional anesthesia with an alternative methodmethod

Large prospective case series to provide Large prospective case series to provide estimates of efficacy and safety (>100 estimates of efficacy and safety (>100 cases)cases)

Definition of EfficacyDefinition of Efficacy Not requiring conversion to an alternative Not requiring conversion to an alternative

anesthetic techniqueanesthetic technique

Liu et al

Basis of the Liu’s Review Basis of the Liu’s Review ArticleArticle

14 Randomized Control Trials (RTCs) for 14 Randomized Control Trials (RTCs) for Peripheral Nerve BlocksPeripheral Nerve Blocks

2 Case Series for Peripheral Nerve Blocks2 Case Series for Peripheral Nerve Blocks 6 RTCs fot Neuro-axial Anesthesia6 RTCs fot Neuro-axial Anesthesia 1 Case Series for Neuroaxial Anesthesia1 Case Series for Neuroaxial Anesthesia

Liu et al

Ultrasound Guided Upper Ultrasound Guided Upper Extremity AnesthesiaExtremity Anesthesia

Seven RTCs compared US Guided regional Seven RTCs compared US Guided regional block to alternative techniqueblock to alternative technique

All trials used regional blockade for All trials used regional blockade for surgical anesthesiasurgical anesthesia

No trial showed significant No trial showed significant differences in efficacy between US differences in efficacy between US guided and alternative techniqueguided and alternative technique (i.e. (i.e. conversion to general anesthesia)conversion to general anesthesia)

Six of the seven showed no difference in Six of the seven showed no difference in supplementation requirementssupplementation requirements

Two of the seven trials measured patient Two of the seven trials measured patient satisfaction and found no differences satisfaction and found no differences between techniquesbetween techniques

Liu et al

Ultrasound Guided Upper Extremity Ultrasound Guided Upper Extremity Anesthesia Continued: Any Advantages?Anesthesia Continued: Any Advantages?

Five Axillary Block StudiesFive Axillary Block Studies Four of Five reported fewer needle passes or Four of Five reported fewer needle passes or

faster time for block performancefaster time for block performance Four of Five reported faster or more complete Four of Five reported faster or more complete

early onset of sensory or motor block (none early onset of sensory or motor block (none reported a significant difference in onset of reported a significant difference in onset of surgical anesthesia)surgical anesthesia)

Soeding et alSoeding et al99 showed earlier sensory or motor showed earlier sensory or motor blockade for interscalene blocks but did not show blockade for interscalene blocks but did not show a difference in duration of analgesiaa difference in duration of analgesia

Williams et al.Williams et al.1010 showed faster block performance showed faster block performance with ultrasound but no difference in onset or with ultrasound but no difference in onset or success during supraclavicular blocksuccess during supraclavicular block

Bucking the Trend: Bucking the Trend: Infraclavicular BlocksInfraclavicular Blocks

Dingeman et alDingeman et al1111

Compared Ultrasound vs. US with Nerve StimulationCompared Ultrasound vs. US with Nerve Stimulation Found US alone resulted in faster block Found US alone resulted in faster block

performance, more complete early blockade and performance, more complete early blockade and less need for supplementationless need for supplementation

Marhofer et alMarhofer et al1212

Compared US with nerve stimulation in childrenCompared US with nerve stimulation in children Found US resulted in less pain during block, faster Found US resulted in less pain during block, faster

block onset and longer duration of sensory blockadeblock onset and longer duration of sensory blockade

Liu et al

Ultrasound Guided Lower Ultrasound Guided Lower Extremity AnesthesiaExtremity Anesthesia

Four RCTs compared US guidance versus Four RCTs compared US guidance versus alternate techniquealternate technique

No RCT found differences in failed blocksNo RCT found differences in failed blocks No RCT reported an persistent complicationsNo RCT reported an persistent complications Two RCTs showed shorter onset time with Two RCTs showed shorter onset time with

US guidanceUS guidance One RCT reported better turniquet tolerance One RCT reported better turniquet tolerance

in midfemoral sciatic block for foot and in midfemoral sciatic block for foot and ankle surgery with the use of ultrasound for ankle surgery with the use of ultrasound for the blockthe block

Local Anesthetic Volume in Local Anesthetic Volume in Lower Extremity Nerve Lower Extremity Nerve

BlockadeBlockade Casati et alCasati et al55 showed a significant reduction showed a significant reduction

in the Mean Effective Anesthetic Volume in the Mean Effective Anesthetic Volume (MEAV(MEAV5050) with the use of ultrasound ) with the use of ultrasound guidance for femoral nerve blockadeguidance for femoral nerve blockade

Oberndorfer et alOberndorfer et al1414 reports both a reports both a significant reduction in required local significant reduction in required local anesthetic for both femoral and sciatic anesthetic for both femoral and sciatic blocks as well as increased duration of blocks as well as increased duration of analgesia for ultrasound guided blocks analgesia for ultrasound guided blocks versus nerve stimulation aloneversus nerve stimulation alone

First Do No First Do No HarmHarm!!

No RCT has shown that other techniques No RCT has shown that other techniques are safer than Ultrasound Guidanceare safer than Ultrasound Guidance

No RCT has shown that other techniques No RCT has shown that other techniques are superior in terms of efficacyare superior in terms of efficacy

No RCT has shown that patient satisfaction No RCT has shown that patient satisfaction is greater with an alternative techniqueis greater with an alternative technique

Is There Evidence of Benefit Is There Evidence of Benefit in the Use of Ultrasound in the Use of Ultrasound

Guidance?Guidance? Faster Block PerformanceFaster Block Performance

Fewer Needle PassesFewer Needle Passes

Faster Initial Onset of BlockadeFaster Initial Onset of Blockade

PossiblePossible Reduced Local Anesthetic Reduced Local Anesthetic RequirementsRequirements

Is There a Safety Benefit in Is There a Safety Benefit in Using Ultrasound Using Ultrasound

Guidance?Guidance? Direct visualization of needle should reduce Direct visualization of needle should reduce

the rate of intraneural and intravascular the rate of intraneural and intravascular puncturespunctures

Reduced local anesthetic requirements Reduced local anesthetic requirements suggests less local anesthetic systemic suggests less local anesthetic systemic toxicity risktoxicity risk

Fewer needle passes suggests less damage to Fewer needle passes suggests less damage to surrounding tissuessurrounding tissues

BOTTOMLINEBOTTOMLINE: Current evidence is : Current evidence is INSUFFICIENTINSUFFICIENT to support these assumptions to support these assumptions given the rarity of significant nerve injury and given the rarity of significant nerve injury and systemic toxicity of local anestheticssystemic toxicity of local anesthetics

The Question RemainsThe Question Remains:: Given that there is no Given that there is no definitive evidence of definitive evidence of increased efficacy or increased efficacy or

safety benefit with the safety benefit with the use of Ultrasound use of Ultrasound Guidance, is this a Guidance, is this a

passing fad or is US passing fad or is US guidance here to stay?guidance here to stay?

Sparrow’s PredictionsSparrow’s Predictions I predict we will see large multi-center I predict we will see large multi-center

studies that show a safety and efficacy studies that show a safety and efficacy benefitbenefit

I predict that the volume of local anesthetic I predict that the volume of local anesthetic used in the future will be significantly used in the future will be significantly smaller than the accepted norms of todaysmaller than the accepted norms of today

I predict US technology will continue to I predict US technology will continue to improve and techniques will become easier improve and techniques will become easier as our collective experience growsas our collective experience grows

Sparrow’s BeliefsSparrow’s Beliefs I believe that Ultrasound guidance will be a I believe that Ultrasound guidance will be a

necessary skill in the future and resident education necessary skill in the future and resident education in the technique should be a top priorityin the technique should be a top priority

I believe that the current body of evidence does not I believe that the current body of evidence does not support the argument for Ultrasound Guidance as support the argument for Ultrasound Guidance as the new standard of care for regional anesthesiathe new standard of care for regional anesthesia

I believe that certification for ultrasound use is a I believe that certification for ultrasound use is a major mistake but there is already a growing major mistake but there is already a growing number of certification proponentsnumber of certification proponents

And finally….I believe the children are our futureAnd finally….I believe the children are our future -Whitney Houston-Whitney Houston

Questions, Questions, Comments…..Standing Comments…..Standing Ovation……Call for an Ovation……Call for an

Encore?Encore?

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