20. Demo: Thoracic ultrasound Flashcards
Ultrasound
High frequency sound waves bounced off internal organs and tissues via array of transducers to produce 2D images
Most commonly used ultrasound
B-mode (2D mode)
3.5 MHz ultrasound probe
Lower resolution images but increased depth of view
Curved array
Good for looking at organs deeper in body
7-12 MHz ultrasound probe
High resolution images but limited depth of view
Linear array
Examining surface of body e.g. identifying veins or surface of lung
Echogenic line
layers of visceral and parietal pleura at lung edge
Describe the movement of lung pleura on an ultrasound
Visceral pleura slides over stationary parietal pleura as patient breathes
What does “gliding pleura” or “sliding lung” show?
That we are looking at a normal lung
There is nothing between the lung edge and chest wall
Describe ‘A’ lines
‘A’ lines run parallel to the lung edge, apparently within the lung but are reverberation artefacts
Move back and forth with ventilation (like an echo of the echogenic line)
What may scanning the ribs aid?
Recognition of lung edge
What are ‘comet tails’ or B line artefacts perpendicular to the lung edge?
Interlobular septa (boundaries between secondary pulmonary lobules)
Describe interlobular septa in a patient with pulmonary oedema
Interlobular septa become enlarged and get distended
You would see many more comet tails than that of a person with a normal lung
M-Mode ultrasound
1 dimensional display of motion (M) of echo-producing interfaces displayed against time (T) along the 2nd axis
M-mode ultrasound of a normal lung
“Sea shore” sign
At lung edge (echogenic line), striking granular white line with sandy appearance behind (movement of lung artefact)
Which plane is very useful for thoracic ultrasound as it eliminates the rib artefact?
Parasagittal plane/ Paracoronal plane
List 6 uses of ultrasound of the thorax
Detect pleural effusion and guide drainage
Differentiate sub-pulmonary from sub-phrenic fluid
Assess tumour invasion of chest wall and pleura
Guide pleural and lung biopsy
Identification of pneumothorax
Assessment of respiratory muscle function
How much fluid outside the lung wall is normal?
A tiny amount because it provides lubrication; allows visceral pleura to slide over parietal pleura.
How much fluid outside the lung is abnormal?
Lots of pleural fluid e.g. 2cm on an ultrasound
Describe muscular work in inspiration
Diaphragm contracts, moves down Scalenes and SCM contract: elevate ribs and move sternum anteriorly- increases volume of hemithorax External intercostals (and interchondral portions of internal intercostals) contract, elevate ribs
Describe muscular work in 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 important nerve innervates the diaphragm?
Phrenic nerve
Nerve roots of phrenic nerve
C3
C4
C5
Positioning of phrenic nerve
Runs down anterior mediastinum, draped over front of heart to supply diaphragm
What does damage to the phrenic nerve cause?
Diaphragmatic paralysis
What do forced inspiration (sniff) tests asses?
Function of phrenic nerve
Describe abnormal and normal sniff tests
Normal: rapid caudal movement (contracts and moves sharply downwards towards the feet)
Abnormal: paradoxical cranial movement
What is the difference in scanning the diaphragm on a CT and an ultrasound?
CT: Diaphragm indistinguishable from liver
Ultrasound: Diaphragm seen well by echogenic stripe
How is the diaphragm viewed? Why?
Diaphragm is obscured by aerated lung so must be looked at from below (sideways scan) (see diaphragm as it moves downwards)
