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Ultrasound

Kevin's Ultrasound Lecture (SIUE Nurse Anesthesia)

QuestionAnswer
What are uses for ultrasound in anesthesia? 1) regional blocks 2) blood vessel cannulation 3) echocardiograms
Is US use better than using landmarks for invasive procedures? Yes. Allows for better visualization of complex anatomical structures.
1 Hz 1 cycle per second
1 MHz 1,000,000 cycle per second
What is the frequency range for ultrasound? 1 MHz to 20 MHz (usually less than 10 MHz)
What do sound waves need to travel? a medium
How will the density of different media affect sound? Will travel at different rate.
What is the term for the speed at which sound travels through specific media? propagation speed
Which state of matter has the lowest propagation speed? gas (least dense)
Which state of matter has the highest propagation speed? solid (most dense)
What is the average propagation speed for sound in body tissues? 1540 m/s
What is the unit of measure for US wavelength? meters and millimeters
Why is wavelength important in US? determines image resolution
What is the definition of wavelength? distance needed for one cycle to occur
What is the definition of frequency? amount of time needed for one cycle to occur
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
What substance does the body share propagation speed with? water
What is the formula for wavelength? Distance = rate x time
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
What does anechoic mean? How do anechoic materials appear on US? do not reflect sound. appear all black on US
What does hypoechoic mean? How do hypoechoic materials appear on US? grey to black. do not reflect sound well.
What does hyperechoic mean? How do hyperechoic materials appear on US? reflect sound well. light grey to white.
Name the 6 components of a US machine. 1) Master synchronizer 2) Pulser 3) Transducer 4) Processor 5) Display device 6) Storage device
What is the trade off with increasing frequency? Increasing wave frequency allows higher resolution but limits tissue penetration
How does contrast adjustment improve US image? produces better view of edges of structures
How should gain be adjusted? most of background should be black
What is the only thing that needs to be adjusted when 1st using ultrasound machine? depth
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.
What property of sound wave changes when objects are moving? frequency of sound (doppler effect)
What does the pulser do? controls firing pattern in transducer
What does transducer do? converts electrical signal from pulser into sound waves
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
What are 2 other terms for long-axis view? 1) longitudinal 2) in-plane
What are 2 other terms for short-axis view? 1) cross-sectional 2) out-of-plane
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.
Describe how muscles appear on US. Featherlike appearance in long axis Uniform darker pattern on short-axis
Describe how tumors appear on US. hyperechoic
Describe how bone appear on US. Linear, white structure, with darker shadow underneath
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
Describe how fascia appear on US. Normal fatty tissue is dark Tumor appears lighter
Describe how pleura appear on US. Appears light with darker cavities
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
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)
What is the best technique for single-injection nerve blocks? in-plane technique
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)
How can US be used for ETT placement? assessing subglotic diameter (for tube size selection)
How can US be used for trach placement? Used to locating trachea for percutaneous dilatational tracheostomy
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.
Created by: toppu2020