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Addition of ultrasound

  1. 1. Ultrasound to the armamentarium: The addition of L. Harold Barnwell III, DNAP, CRNA Staff Anesthetist & Clinical Instructor VCU Health System Dept. Nurse Anesthesia an introduction to ultrasound physics and image optimization.
  2. 2. Objectives Review basic physics of sound Describe sound & tissue interaction Discuss anatomical imaging with ultrasound Explain causes for clinically relevant artifact Name basic components and functions of an ultrasound apparatus (“knobology”) Review safety, complications, and strategies to reduce error
  3. 3. 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 History
  4. 4. 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 20–100 kHz for navigation and spatial orientation”
  5. 5. Hertz (Hz)? Hertz – “the standard unit of frequency…equal to one cycle per second” (4)
  6. 6. Ultrasound? λ= the wavelength of 1 cycle 1 cycle = compressio n + rarefaction
  7. 7. 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
  8. 8. Linear Array High Frequency SonoSite M Turbo (Hockey Stick Transducer) (Low Frequency Curved Linear Array Transducer)
  9. 9. Application
  10. 10. Ultrasound Guided Interscalene Depth: Brachial Plexus is typically visualized 1-3cm below the skin
  11. 11. Practical Application *High frequency* More cycles per second Images are higher resolution Increased attenuation Imaging limited to shallow depths Low frequency Fewer cycles per second Greater tissue penetration but lower resolution Less attenuation allows for imaging of deeper structures
  12. 12. Practical Application High frequency (7mHz)…higher resolution Low frequency (4mHz)…deeper structures
  13. 13. Transducer Basics
  14. 14. Transducer Basics A. Focal Zone A. Lateral Resolution A. Axial Resolution
  15. 15. DEPTH…determined by time (from when the ultrasound wave (“pulse”) was sent to when echo received) BRIGHTNESS…echo strength (results from differences in acoustic impedance between adjacent tissues) Image Creation
  16. 16. Propagation Velocities
  17. 17. Acoustic Impedance
  18. 18. Brachial Artery anechoi c circle Image Creation B-Mode (2-D) Image…
  19. 19. Image Creation Angle of : - Reflection - Refraction - Scattering - Attenuation
  20. 20. Image Creation
  21. 21. Reflection Bone… Specular Reflector (“mirror like”) Bright white…Strong echo… Acoustic Impedance
  22. 22. Diffuse Reflection Refraction
  23. 23. 7 microns 300 microns Rayleigh Scattering
  24. 24. Attenuation (by first rib)…specul ar reflector “shadowing ” below rib Pleura (Supraclavicular Image of the Brachial Plexus) Attenuation
  25. 25. Attenuation Coefficients
  26. 26. Nerves – appear as round, dark (anechoic) or “honeycomb” structures in cross sectional view Tissue Appearance
  27. 27. Nerves – appear as round, dark (anechoic) or “honeycomb” structures in cross sectional view Tissue Appearance Vasculature – appear as round, dark (anechoic) structures in cross sectional view; tubular in longitudinal view…*color/doppl
  28. 28. Round (short-axis) & tubular (long-axis) Pulsatile in nature Difficult to compress Color/Doppler Signal Tissue Appearance Ovoid in short-axis and tube-like in long-axis Easily compressible Valves may be visible Color/Doppler Signal Artery or Vein? Artery or Vein?
  29. 29. Fat – hypoechoic areas with streaks of irregular hyperechoic lines Muscle – feather- like in longitudinal view; “starry night in cross-section Fascia – thin linear hyperechoic structures marking tissue boundaries Tissue Appearance Fat Muscl e Fasci a
  30. 30. Fat – most superficial layer imaged Muscle – heterogeneous due to different acoustic impedances between cell structures, the water content within the cells, and the fascia Fascia – creates tissue planes, felt as Tissue Appearance Fat Muscl e Fasci a
  31. 31. Tendons – appear similar to nerves at the joint, but become flat and disappear when followed toward the muscle belly Cysts – similar vascular structures, however appear as hypoechoic circles in longitudinal view Bone – hyperechoic linear structures with shadowing underneath Tendon Median Nerve Bone Tissue Appearance
  32. 32. Doppler Effect Clinical Application: RED ARTERY Christian Doppler
  33. 33. Doppler Effect
  34. 34. Phenomenon that affects the acquisition or interpretation of an ultrasound image Can 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
  35. 35. CAUSE: Transducer does not fully contact the skin TIP: Commonly occurs when imaging smaller structures CORRECTION: Add gel and apply even pressure to the Air Artifact (avoid)
  36. 36. CAUSE: Ultrasound pulse contacts strong reflector, amplitude of the beam distal to structure is diminished…hypoec hoic distal image Tip: shadowing below the first rib is good imaging for supraclavicular block Shadow (recognize)
  37. 37. CAUSE: Sound passes through tissue with low acoustic impedance (blood vessel) …then contacts tissue with higher impedance…creat es the “appearance” of a more echogenic Acoustic Enhancement (recognize)
  38. 38. CAUSE: Sound trapped between two highly reflective surfaces Mirror Image (recognize)
  39. 39. CAUSE: sound reflects off two strong specular reflectors separated by a thin layer of air (i.e. needle) or fluid…an illusion of “multiple” structures are displayed below the actual one TIP: Occurs with good “in-plane” Reverberation (recognize)
  40. 40. Ergonomics Transducer Selection Orientation Transducer Handling Gain & Depth Scanning Principles for Image Optimization
  41. 41. Appropriate bed height Ultrasound in line with the provider and patient Scanning arm supported Assistant (if available) Proper transducer handling Ergonomics
  42. 42. Linear Array High Frequency SonoSite M Turbo (Hockey Stick Transducer) (Low Frequency Curved Linear Array Transducer)
  43. 43. Proper Orientation Orientation Notch to the ANESTHETIST’s LEFT
  44. 44. Transducer Orientation Orientation Notch to the ANESTHETIST’s LEFT
  45. 45. Proper Orientation
  46. 46. Improper Orientation
  47. 47. In-Plane Approach Needle Visualization
  48. 48. Out-of-Plane Needle Visualization
  49. 49. Flat against the skin for maximal contact Hold 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
  50. 50. Transducer Handling CORRECT “Low” Hand Position Improper Hand Position (high on the transducer) …hand will easily
  51. 51. SLIDE COMPRESS TILT ROTATE ROCK Transducer Movements
  52. 52. Cross-Section or Short-Axis View Longitudinal or Long-AxisView B-mode Imaging (2-D)
  53. 53. Gain “…Goldilocks Principle” Too Little Too Much “Snowstorm”“Blackout”
  54. 54. Gain Adjustments Near gain Far gain Total gain “Autogain”
  55. 55. Gain “Just Right” Gain “…Goldilocks Principle”
  56. 56. Depth determines how far into tissues echoes are interpreted Increased depth…decreased resolution Structure of interest is kept in the center of the screen Depth
  57. 57. 6 cm Too Much Depth 1.3 cm (½ in)Brachial Artery Depth
  58. 58. 1.3 cm (½ in) 2.7cm “Just Right”” Depth
  59. 59. Color-Flow Doppler
  60. 60. WHAT NOW? You have the right patient, discussed the proposed anesthetic technique, obtained consent, verified the site, and gathered your supplies Select the appropriate frequency transducer Imagine how the image should appear on the monitor Use good ergonomics Apply sufficient gel to the transducer
  61. 61. OPTIMIZE THE IMAGE Use PLENTY of gel. Gel acts as a coupler between the transducer and the skin, and improves the image quality Ensure 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 screen Adjust your gain to make picture look uniform
  62. 62. ANATOMY Know 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
  63. 63. SAFETY STRATEGIES Ultrasound itself is non-invasive Ultrasound-guided procedures introduce a needle and/or local anesthetic into the patient increasing the potential for complications Needle insertion should first be practiced using a phantom numerous times, with emphasis placed viewing the entire needle as it passes through the tissue Strategies such as wiggling, or hydro-location can be used to verify the location of the needle tip
  64. 64. Christian Falyar CRNA, DNAP
  65. 65. QUESTIONS?
  66. 66. REFERENCES AANA News & Journal: Commends-Senate-Veterans-Affairs-Committee-for-Working-to-Improve-Veterans-Access-to- Quality-Healthcare.aspx Aldrich 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.
  67. 67. REFERENCES Marhofer 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 learner’s 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. Xu 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. onid=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;