Ultrasound

Ultrasound

to the armamentarium:The addition ofL. Harold Barnwell III, DNAP, CRNAStaff Anesthetist & Clinical InstructorVCU Health System Dept. Nurse Anesthesiaan introduction to ultrasound physics and image optimization.

ObjectivesReview basic physics of soundDescribe sound & tissue interactionDiscuss anatomical imaging with ultrasoundExplain causes for clinically relevant artifactName basic components and functions of an ultrasound apparatus (knobology)Review safety, complications, and strategies to reduce error

1880: Pierre and Jacques Curie discovered the piezoelectric effect in crystals. 1915: Ultrasound was used by the navy for detecting submarines.

1942: Karl and Dussik described ultrasound use as a diagnostic tool.

1978: P. La Grange published the first case-series of ultrasound application for placement of needles for nerve blocks. (doppler)

1989: P. Ting and V. Sivagnanaratnam used ultrasonography to demonstrate the anatomy of the axilla and to observe the spread of local anesthetics during axillary block.

1994: Steven Kapral and colleagues explored brachial plexus blockade using B-mode ultrasound.

History

Ultrasound?Sound the sensation produced by stimulation of the organs of hearing by vibrations transmitted through the air or other medium Ultrasound sound with a frequency greater than 20,000 hertz, approximately the upper limit of human hearing Bats & Dolphins can produce sounds 20100 kHz for navigation and spatial orientation

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Hertz (Hz)?Hertz the standard unit of frequencyequal to one cycle per second (4)

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Ultrasound?

= the wavelength of 1 cycle1 cycle = compression + rarefaction

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Piezoelectric Effect

phenomenon exhibited by the generation of an electric charge in response to a mechanical force (squeeze or stretch) applied on certain materials.

E > M

E < M

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Linear Array High Frequency Transducer

SonoSite M Turbo

(Hockey Stick Transducer)(Low Frequency Curved Linear Array Transducer)

Application

Ultrasound Guided InterscaleneDepth: Brachial Plexus is typically visualized 1-3cm below the skin

Practical Application*High frequency*More cycles per secondImages are higher resolution Increased attenuationImaging limited to shallow depths

Low frequencyFewer cycles per secondGreater tissue penetration but lower resolutionLess attenuation allows for imaging of deeper structures*Neuraxial Imaging

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Practical ApplicationHigh frequency (7mHz)higher resolution

Low frequency (4mHz)deeper structures

Transducer Basics

Transducer Basics

Focal Zone

Lateral Resolution

Axial Resolution

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DEPTHdetermined by time (from when the ultrasound wave (pulse) was sent to when echo received)BRIGHTNESSecho strength(results from differences in acoustic impedance between adjacent tissues)

Image Creation

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Propagation Velocities

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Acoustic Impedance

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Brachial Arteryanechoic circleImage Creation

B-Mode (2-D) Image

Image CreationAngle of :

- Reflection

- Refraction

- Scattering

- Attenuation

Image Creation

Reflection

Bone Specular Reflector (mirror like) Bright whiteStrong echoAcoustic Impedance

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Diffuse Reflection

Refraction

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7 microns300 microns

Rayleigh Scattering

Attenuation (by first rib)specular reflector

shadowing below ribPleura

(Supraclavicular Image of the Brachial Plexus)Attenuation

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Attenuation Coefficients

Nerves appear as round, dark (anechoic) or honeycomb structures in cross sectional viewTissue Appearance

Nerves appear as round, dark (anechoic) or honeycomb structures in cross sectional viewTissue Appearance

Vasculature appear as round, dark (anechoic) structures in cross sectional view; tubular in longitudinal view*color/doppler

Round (short-axis) & tubular (long-axis)Pulsatile in natureDifficult to compressColor/Doppler Signal

Tissue Appearance

Ovoid in short-axis and tube-like in long-axisEasily compressibleValves may be visible Color/Doppler Signal

Artery or Vein?Artery or Vein?

Fat hypoechoic areas with streaks of irregular hyperechoic lines Muscle feather-like in longitudinal view; starry night in cross-sectionFascia thin linear hyperechoic structures marking tissue boundaries

Tissue Appearance

FatMuscleFascia

Fat most superficial layer imagedMuscle heterogeneous due to different acoustic impedances between cell structures, the water content within the cells, and the fascia Fascia creates tissue planes, felt as pops as needle passes throughTissue Appearance

FatMuscleFascia

Tendons appear similar to nerves at the joint, but become flat and disappear when followed toward the muscle bellyCysts similar vascular structures, however appear as hypoechoic circles in longitudinal view Bone hyperechoic linear structures with shadowing underneath

TendonMedian Nerve

BoneTissue Appearance

Doppler Effect

Clinical Application: RED ARTERY

BLUE VEIN

Christian Doppler

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Doppler Effect

Phenomenon that affects the acquisition or interpretation of an ultrasound imageCan result from:Properties of sound (recognize)Tissue / sound interaction (recognize)*Created by the provider (AVOID)The most common artifacts are air artifact, shadow artifact, acoustic enhancement, mirror image and reverberation

Artifacts

CAUSE: Transducer does not fully contact the skinTIP: Commonly occurs when imaging smaller structuresCORRECTION: Add gel and apply even pressure to the trasducer

Air Artifact (avoid)

CAUSE: Ultrasound pulse contacts strong reflector, amplitude of the beam distal to structure is diminishedhypoechoic distal image Tip: shadowing below the first rib is good imaging for supraclavicular block

Shadow (recognize)

CAUSE: Sound passes through tissue with low acoustic impedance (blood vessel) then contacts tissue with higher impedancecreates the appearance of a more echogenic tissue below

Acoustic Enhancement(recognize)

CAUSE: Sound trapped between two highly reflective surfaces

Mirror Image(recognize)

CAUSE: sound reflects off two strong specular reflectors separated by a thin layer of air (i.e. needle) or fluidan illusion of multiple structures are displayed below the actual oneTIP: Occurs with good in-plane imaging of the needle

Reverberation (recognize)

ErgonomicsTransducer SelectionOrientationTransducer HandlingGain & DepthColor /Doppler

Scanning Principles for Image Optimization

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Appropriate bed heightUltrasound in line with the provider and patientScanning arm supportedAssistant (if available)Proper transducer handling

Ergonomics

Linear Array High Frequency Transducer

SonoSite M Turbo

(Hockey Stick Transducer)(Low Frequency Curved Linear Array Transducer)

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Proper OrientationOrientation Notch to the ANESTHETISTs LEFT

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Transducer Orientation

Orientation Notch to the ANESTHETISTs LEFT

Proper Orientation

Improper Orientation

In-Plane Approach

needle

Needle Visualization

Out-of-Plane

Needle Visualization

Flat against the skin for maximal contactHold low on the transducer (like a pencil)Support the scanning arm; rest it on a firm surface (i.e. the patient)Apply firm, but gentle pressure

Transducer Handling

Transducer Handling

CORRECT Low Hand PositionImproper Hand Position (high on the transducer)hand will easily fatigue

SLIDECOMPRESSTILTROTATEROCKTransducer Movements

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Cross-Section orShort-Axis ViewLongitudinal orLong-AxisView

B-mode Imaging (2-D)

GainGoldilocks Principle

Too LittleToo MuchSnowstormBlackout

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Gain Adjustments

Near gainFar gainTotal gainAutogain

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Gain Just Right

GainGoldilocks Principle

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Depth determines how far into tissues echoes are interpretedIncreased depthdecreased resolution Structure of interest is kept in the center of the screen

Depth

6 cmToo MuchDepth1.3 cm ( in)Brachial Artery

Depth

1.3 cm ( in)2.7cmJust Right

Depth

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Color-Flow Doppler

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WHAT NOW?You have the right patient, discussed the proposed anesthetic technique, obtained consent, verified the site, and gathered your suppliesSelect the appropriate frequency transducerImagine how the image should appear on the monitorUse good ergonomicsApply sufficient gel to the transducerJump in!

OPTIMIZE THE IMAGEUse PLENTY of gel. Gel acts as a coupler between the transducer and the skin, and improves the image qualityEnsure your transducer is initially perpendicular and flat against the skin Optimize your depth so the structures you wish to image are in the center of the screenAdjust your gain to make picture look uniform

ANATOMYKnow it. Most nerves blocked using regional anesthesia are in close proximity to arteries, veins, or other vital organs (i.e. the lungs)Anticipate what you will be seeing before you start scanning.Proper orientation of the picture make your picture appear correctly

SAFETY STRATEGIESUltrasound itself is non-invasiveUltrasound-guided procedures introduce a needle and/or local anesthetic into the patient increasing the potential for complicationsNeedle insertion should first be practiced using a phantom numerous times, with emphasis placed viewing the entire needle as it passes through the tissueStrategies such as wiggling, or hydro-location can be used to verify the location of the needle tip

vaultrasound.com

Christian Falyar CRNA, DNAP

QUESTIONS?

REFERENCESAANA News & Journal: http://www.aana.com/newsandjournal/News/Pages/072015-AANA-Commends-Senate-Veterans-Affairs-Committee-for-Working-to-Improve-Veterans-Access-to-Quality-Healthcare.aspxAldrich J E. Basic physics of ultrasound imaging. Crit Care Med. 2007;35(5 Suppl):S131-S137.Bigeleisen PE, ed, Orebaugh SL, Moayeri N, et al. Ultrasound-guided regional anesthesia ad pain medicine. Baltimore, MD. Lippincott Williams & Wilkins; 2010:26-33.Falyar CR. Ultrasound in anesthesia: applying scientific principles to clinical practice. AANA J. 2010 Aug; 78(4):332-40.Gray AT. Atlas of ultrasound-guided regional anesthesia. Philadelphia, PA. Saunders, Elsevier; 2010:45-67.Kossoff G. Basic physics and imaging characteristics of ultrasound. World J Surg. 2000; 24:134-142.Kremkau F W. Doppler Ultrasound: Principles and Instruments. Philadelphia, PA: W.B. Saunders Company; 1990:5-51.

REFERENCESMarhofer P, Frickey N. Ultrasonographic guidance in pediatric regional anesthesia part 1: Theoretical background. Paed Anaesth. 2006;16(10):1008-1018.Pollard BA, Chan VW. An introductory curriculum for ultrasound-guided regional anesthesia: a learners guide. Toronto. University of Toronto Press Inc.; 2009:23-28.Sites B D, Brull R, Chan V W, et al. Artifacts and pitfall errors associated with ultrasound-guided regional anesthesia. part I: understanding the basic principles of ultrasound physics and machine operations. Reg Anesth Pain Med 2007;32(5):412-418.Taylor K J, Holland S. Doppler us. part i. basic principles, instrumentation, and pitfalls. Radiology. 1990; 174(2):297-307.www.vaultrasound.comXu D. Xu D Xu, Daquan.Chapter 26. Ultrasound Physics. In: Hadzic A. Hadzic A Ed. Admir Hadzic.eds. Hadzic's Peripheral Nerve Blocks and Anatomy for Ultrasound-Guided Regional Anesthesia, 2e. New York, NY: McGraw-Hill; 2012. http://accessanesthesiology.mhmedical.com.proxy.library.vcu.edu/content.aspx?bookid=518&Sectionid=41534315. Accessed September 02, 2015.Zagzebski JA. Physics and instrumentation in Doppler and B-mode ultrasonography. In: Zweibel WJ. Introduction to Vascular Ultrasonography. 4th ed. Philadelphia, PA: W.B. Saunders Company; 2000:17-43.