Demo: Thoracic ultrasound Flashcards
What is meant by ultrasound
High frequency sound waves bounced off internal aging of organs and tissues via array of transducers to produce 2D images
Most commonly called B-mode or 2D mode
What is the role of the transducer
Calculates how deep the structure is in the body, based on how quickly they reach the transducer
Describe the use of the 3.5MHz probe
Lower resolution images but increased depth of view
Used to image deep organs (liver, kidney or diaphragm)
Has a curved array to produce a fan of ultrasound that can get around the curvature of the ribs
Describe the use of a 7-12MHz probe
High resolution images but limited depth of view
Used to image short distance entities at the surface of the body- used for inserting central lines- good for surface of lung (pneumothorax or pleural effusion)
How do the visceral and parietal pleura on ultrasound
Very bright echogenic line
As the patient breathes- the parietal moves over the stationary visceral pleura- echogenic line slides in breathing
What may be present below the echogenic line
‘A’ lines run parallel to the lung edge, apparently within the lung but are artefacts
What causes these artefacts
A lines are echoes of the echogenic line- some aren’t reflected backwards- causing a reverberation artefact
What may aid recognition of the lung edge
Scanning across the ribs may aid recognition of lung edge
Why is there are shadow behind the ribs
All the sound is reflected by the cortical bone- none passes through
What is a consequence of the lungs being full of air
All the sound is reflected back
What are ‘comet tails’
Comet tail’or B line artefacts perpendicular to lung edge = interlobular septa
where the interlobular septa comes to the lung surface
What are the interlobular septa
boundaries between secondary pulmonary lobules
What happens in pulmonary oedema
interlobular septa become enlarged (filled with fluid)- see more of them- should expect to see only one or two.
Describe M-mode ultrasound
One dimensional display of motion (M) of echo-producing interfaces displayed against time (T) along the second axis
motion towards or away from the transducer is observed with time and can be used to assess the function of the heart valves (Echocardiogram)
Describe the sea shore line seen in M-mode
Normal M-Mode: should be the sea shore sign; lung pleura should look striated and lung sandy while chest wall should be comprised of straight lines
Which planes can ultrasound use
all of them
Describe ultrasound in the transverse or axial plane
right of patient on left of image (like CT)
Describe ultrasound in the longitudinal or coronal plane
cranial left, caudal right- but lots of rib artefacts
Describe the use of ultrasound in the paracoronal or parasaggital plane
very useful for thoracic US (eliminates rib artefact)
taken at an oblique angle to coronal plane
Describe the use of longitudinal, saggital plane
cranial left, caudal right
What are the uses of thoracic ultrasound
Detect pleural effusion and guide drainage
Differentiate sub-pulmonary from sub-phrenic fluid
Assess tumour invasion of chest wall and pleura- echogenic line will disappear
Guide pleural and lung biopsy
Identification of pneumothorax
Assessment of respiratory muscle function- high diaphragm is weakened (can get fluid under the diaphragm)
How does fluid appear on ultrasound
Completely black
How much pleural fluid is normal
a trace (to allow pleura to slide over each other easily)
How do we determine the volume of pleural fluid
200 x depth of black line = volume of fluid in chest (ml)
List the respiratory muscles
Diaphragm
Internal intercostals
External intercostals
Accessory muscles (attached to sternum, clavicles and scapulae) sternocleidomastoid, scalenes, serratus, pectorals abdominal wall muscles
What is a consequence of a large pleural effusion
Compresses the alveoli- reducing gas exchange
How does a paralysed diaphragm appear
Constantly relaxed and so moves up higher than it would in expiration
due to phrenic nerve damage or liver enlargement on right
can also be caused by trapped air
Summarise inspiration
Diaphragm contracts, moves down Scalenes and SCM contract and elevate ribs and move sternum anteriorly External intercostals (and interchondral portions of internal intercostals) contract, elevate ribs
Summarise expiration
Diaphragm relaxes, moves up Scalenes and SCM relax, ribs move down and sternum drops posteriorly Internal intercostals (except interchondral portions) contract (aided by abdominal muscles), ribs move down
What are the muscles of inspiration
Diaphragm External intercostals Interchondral part of intercostals Scalenes Sternocleidomastoid
What are the muscles of expiration
Internal intercostals (excluding interchondral part) External oblique Internal oblique Transversus abdominus
Rectus abdominus
What is the use of the sniff test
tests function of phrenic nerve
Assess movement of diaphragm
Normal: rapid caudal movement
Abnormal: paradoxical cranial movement
How did we assess diaphragm function in the past
Fluoroscopy- real time X-ray
What is the issue with CT
Diaphragm indistinguishable from Liver
How does the diaphragm appear on US
Diaphragm on US: echogenic line below liver - must be examined from below as lung will block view of diaphragm
Why do we need to look at the diaphragm from below
Diaphragm is obscured by aerated lung so must be looked at from below
What should happen in the sniff test
On sniffing the normally innervated diaphragm contracts and moves sharply downwards (towards the feet, caudally)
