2015 NCANA Annual Meeting

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. 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. 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. 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. Hertz (Hz)?
Hertz – “the standard unit of
frequency…equal to one cycle per
second” (4)

6. Ultrasound?
λ= the
wavelength
of 1 cycle
1 cycle =
compressio
n +
rarefaction

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. Linear Array
High
Frequency
SonoSite
M Turbo
(Hockey Stick
Transducer)
(Low Frequency Curved
Linear Array Transducer)

9. Application

10. Ultrasound
Guided
Interscalene
Depth: Brachial
Plexus is typically
visualized 1-3cm
below the skin

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. Practical Application
High frequency
(7mHz)…higher
resolution
Low frequency
(4mHz)…deeper
structures

13. Transducer Basics

14. Transducer Basics
A. Focal
Zone
A. Lateral
Resolution
A. Axial
Resolution

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. Propagation Velocities

17. Acoustic Impedance

18. Brachial Artery
anechoi
c circle
Image Creation
B-Mode (2-D) Image…

19. Image
Creation
Angle of :
- Reflection
- Refraction
- Scattering
- Attenuation

20. Image Creation

21. Reflection
Bone… Specular
Reflector (“mirror
like”)
Bright white…Strong
echo…
Acoustic
Impedance

22. Diffuse
Reflection
Refraction

23. 7
microns
300 microns
Rayleigh Scattering

24. Attenuation
(by first
rib)…specul
ar reflector
“shadowing
” below rib
Pleura
(Supraclavicular Image of the Brachial
Plexus)
Attenuation

25. Attenuation Coefficients

26. Nerves – appear as
round, dark
(anechoic) or
“honeycomb”
structures in cross
sectional view
Tissue Appearance

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. 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. 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. 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. 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. Doppler Effect
Clinical
Application:
RED
ARTERY
Christian
Doppler

33. Doppler Effect

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. 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. 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. 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. CAUSE:
Sound trapped
between two
highly
reflective
surfaces
Mirror Image
(recognize)

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. Ergonomics
Transducer
Selection
Orientation
Transducer
Handling
Gain & Depth
Scanning Principles
for Image
Optimization

41. Appropriate bed height
Ultrasound in line with
the provider and patient
Scanning arm
supported
Assistant (if available)
Proper transducer
handling
Ergonomics

42. Linear Array
High
Frequency
SonoSite
M Turbo
(Hockey Stick
Transducer)
(Low Frequency Curved
Linear Array Transducer)

43. Proper Orientation
Orientation
Notch to the
ANESTHETIST’s
LEFT

44. Transducer
Orientation
Orientation Notch to the ANESTHETIST’s
LEFT

45. Proper Orientation

46. Improper Orientation

47. In-Plane
Approach
Needle Visualization

48. Out-of-Plane
Needle Visualization

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. Transducer
Handling
CORRECT
“Low” Hand Position
Improper Hand
Position
(high on the
transducer)
…hand will easily

51. SLIDE
COMPRESS
TILT
ROTATE
ROCK
Transducer
Movements

52. Cross-Section or
Short-Axis View
Longitudinal or
Long-AxisView
B-mode Imaging (2-D)

53. Gain
“…Goldilocks
Principle”
Too Little Too Much
“Snowstorm”“Blackout”

54. Gain Adjustments
Near gain
Far gain
Total gain
“Autogain”

55. Gain “Just Right”
Gain
“…Goldilocks
Principle”

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. 6 cm
Too Much
Depth
1.3 cm (½ in)Brachial Artery
Depth

58. 1.3 cm (½ in)
2.7cm
“Just Right””
Depth

59. Color-Flow Doppler

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. 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. 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. 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. vaultrasound.com
Christian Falyar
CRNA, DNAP

65. QUESTIONS?

67. REFERENCES
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Falyar CR. Ultrasound in anesthesia: applying scientific principles to clinical practice. AANA J.
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Gray AT. Atlas of ultrasound-guided regional anesthesia. Philadelphia, PA. Saunders, Elsevier;
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Kremkau F W. Doppler Ultrasound: Principles and Instruments. Philadelphia, PA: W.B. Saunders
Company; 1990:5-51.

68. REFERENCES
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