Kevin's Ultrasound Lecture (SIUE Nurse Anesthesia)
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| What are uses for ultrasound in anesthesia? | 1) regional blocks
2) blood vessel cannulation
3) echocardiograms
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| Is US use better than using landmarks for invasive procedures? | Yes.
Allows for better visualization of complex anatomical structures.
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| 1 Hz | 1 cycle per second
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| 1 MHz | 1,000,000 cycle per second
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| What is the frequency range for ultrasound? | 1 MHz to 20 MHz (usually less than 10 MHz)
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| What do sound waves need to travel? | a medium
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| How will the density of different media affect sound? | Will travel at different rate.
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| What is the term for the speed at which sound travels through specific media? | propagation speed
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| Which state of matter has the lowest propagation speed? | gas (least dense)
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| Which state of matter has the highest propagation speed? | solid (most dense)
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| What is the average propagation speed for sound in body tissues? | 1540 m/s
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| What is the unit of measure for US wavelength? | meters and millimeters
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| Why is wavelength important in US? | determines image resolution
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| What is the definition of wavelength? | distance needed for one cycle to occur
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| What is the definition of frequency? | amount of time needed for one cycle to occur
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| Selected velocities for sound in different media. | Air 331
Fat 1450
Water 1540
Soft tissue 1540
Brain 1541
Liver 1549
Kidney 1561
Blood 1570
Muscle 1585
Lens of eye 1620
Skull-bone 4080
Brass 4490
Aluminum 6400
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| What substance does the body share propagation speed with? | water
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| What is the formula for wavelength? | Distance = rate x time
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| Which two factors are measured by the US probe to determine the depth and density of the media? | 1) timing of sound reflection
2) energy of sound reflection
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| What does anechoic mean? How do anechoic materials appear on US? | do not reflect sound.
appear all black on US
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| What does hypoechoic mean? How do hypoechoic materials appear on US? | grey to black.
do not reflect sound well.
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| What does hyperechoic mean? How do hyperechoic materials appear on US? | reflect sound well.
light grey to white.
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| Name the 6 components of a US machine. | 1) Master synchronizer
2) Pulser
3) Transducer
4) Processor
5) Display device
6) Storage device
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| What is the trade off with increasing frequency? | Increasing wave frequency allows higher resolution but limits tissue penetration
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| How does contrast adjustment improve US image? | produces better view of edges of structures
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| How should gain be adjusted? | most of background should be black
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| What is the only thing that needs to be adjusted when 1st using ultrasound machine? | depth
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| What is the purpose of doppler? | 1) assess presence of flow
2) assesses direction and speed of flow
3) distinguishes between nerves/tendons and blood vessels.
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| What property of sound wave changes when objects are moving? | frequency of sound (doppler effect)
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| What does the pulser do? | controls firing pattern in transducer
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| What does transducer do? | converts electrical signal from pulser into sound waves
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| Tips for getting best image. | Depth suitable for structure being imaged
Center image on screen
May need to compress skin for deeper structures
Angle of probe to skin is best at 90 degrees
Subtle pressure, angulation, movement can make improvements
Have directions lined up right
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| What are 2 other terms for long-axis view? | 1) longitudinal
2) in-plane
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| What are 2 other terms for short-axis view? | 1) cross-sectional
2) out-of-plane
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| Describe how nerves and tendons appear on US. | appear dark or bright depending on nerve size, frequency, & beam angle.
Round, oval, or triangular.
Not compressible.
Hypoechoic areas encircled by a relatively hyper echoic area.
Honeycomb pattern.
Nerves and tendons have similar appearance.
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| Describe how muscles appear on US. | Featherlike appearance in long axis
Uniform darker pattern on short-axis
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| Describe how tumors appear on US. | hyperechoic
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| Describe how bone appear on US. | Linear, white structure, with darker shadow underneath
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| Describe how fat appear on US. | Lumen appears dark to black on short-axis
Arteries have more defined circular structure, are pulsatile, and cannot be easily compressed
Veins are nonpulsatile and can be easily compressed
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| Describe how fascia appear on US. | Normal fatty tissue is dark
Tumor appears lighter
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| Describe how pleura appear on US. | Appears light with darker cavities
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| Describe how needles appear on US. | Appears light, adjust gain to give darker background
Larger needle easier to see, bevel toward or away from beam
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| Describe how artifacts appear on US. | Echoes without anatomical correlation
Lack of ultrasonic beam reflection may occur with loss of 90-degree incidence angle b/t probe and structure (needle must be perpendicular with probe)
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| What is the best technique for single-injection nerve blocks? | in-plane technique
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| What is the best technique for vascular cannulation and continuous nerve caths? | out-of-plane technique (then can switch to in-plane view to view cannula in vessel)
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| How can US be used for ETT placement? | assessing subglotic diameter (for tube size selection)
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| How can US be used for trach placement? | Used to locating trachea for percutaneous dilatational tracheostomy
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| What are the advantages of US for nerve block? | 1) Ability to repeat block at same site when it begins to dissipate.
2) Use when nerve stimulation is not practical.
3) less time.
4) less anesthetic.
5) no radiation exposure.
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