Demo: Thoracic ultrasound

Question 1

What is meant by ultrasound

Answer 1

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

Question 2

What is the role of the transducer

Answer 2

Calculates how deep the structure is in the body, based on how quickly they reach the transducer

Question 3

Describe the use of the 3.5MHz probe

Answer 3

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

Question 4

Describe the use of a 7-12MHz probe

Answer 4

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)

Question 5

How do the visceral and parietal pleura on ultrasound

Answer 5

Very bright echogenic line

As the patient breathes- the parietal moves over the stationary visceral pleura- echogenic line slides in breathing

Question 6

What may be present below the echogenic line

Answer 6

‘A’ lines run parallel to the lung edge, apparently within the lung but are artefacts

Question 7

What causes these artefacts

Answer 7

A lines are echoes of the echogenic line- some aren’t reflected backwards- causing a reverberation artefact

Question 8

What may aid recognition of the lung edge

Answer 8

Scanning across the ribs may aid recognition of lung edge

Question 9

Why is there are shadow behind the ribs

Answer 9

All the sound is reflected by the cortical bone- none passes through

Question 10

What is a consequence of the lungs being full of air

Answer 10

All the sound is reflected back

Question 11

What are ‘comet tails’

Answer 11

Comet tail’or B line artefacts perpendicular to lung edge = interlobular septa
where the interlobular septa comes to the lung surface

Question 12

What are the interlobular septa

Answer 12

boundaries between secondary pulmonary lobules

Question 13

What happens in pulmonary oedema

Answer 13

interlobular septa become enlarged (filled with fluid)- see more of them- should expect to see only one or two.

Question 14

Describe M-mode ultrasound

Answer 14

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)

Question 15

Describe the sea shore line seen in M-mode

Answer 15

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

Question 16

Which planes can ultrasound use

Answer 16

all of them

Question 17

Describe ultrasound in the transverse or axial plane

Answer 17

right of patient on left of image (like CT)

Question 18

Describe ultrasound in the longitudinal or coronal plane

Answer 18

cranial left, caudal right- but lots of rib artefacts

Question 19

Describe the use of ultrasound in the paracoronal or parasaggital plane

Answer 19

very useful for thoracic US (eliminates rib artefact)

taken at an oblique angle to coronal plane

Question 20

Describe the use of longitudinal, saggital plane

Answer 20

cranial left, caudal right

Question 21

What are the uses of thoracic ultrasound

Answer 21

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)

Question 22

How does fluid appear on ultrasound

Answer 22

Completely black

Question 23

How much pleural fluid is normal

Answer 23

a trace (to allow pleura to slide over each other easily)

Question 24

How do we determine the volume of pleural fluid

Answer 24

200 x depth of black line = volume of fluid in chest (ml)

Question 25

List the respiratory muscles

Answer 25

Diaphragm
Internal intercostals
External intercostals

Accessory muscles (attached to sternum, clavicles and scapulae)
sternocleidomastoid, scalenes, serratus, pectorals
abdominal wall muscles

Question 26

What is a consequence of a large pleural effusion

Answer 26

Compresses the alveoli- reducing gas exchange

Question 27

How does a paralysed diaphragm appear

Answer 27

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

Question 28

Summarise inspiration

Answer 28

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

Question 29

Summarise expiration

Answer 29

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

Question 30

What are the muscles of inspiration

Answer 30

Diaphragm 
External intercostals
Interchondral part of intercostals 
Scalenes 
Sternocleidomastoid

Question 31

What are the muscles of expiration

Answer 31

Internal intercostals
(excluding interchondral part) 
External oblique
Internal oblique 
Transversus abdominus

Rectus abdominus

Question 32

What is the use of the sniff test

Answer 32

tests function of phrenic nerve
Assess movement of diaphragm

Normal: rapid caudal movement

Abnormal: paradoxical cranial movement

Question 33

How did we assess diaphragm function in the past

Answer 33

Fluoroscopy- real time X-ray

Question 34

What is the issue with CT

Answer 34

Diaphragm indistinguishable from Liver

Question 35

How does the diaphragm appear on US

Answer 35

Diaphragm on US: echogenic line below liver - must be examined from below as lung will block view of diaphragm

Question 36

Why do we need to look at the diaphragm from below

Answer 36

Diaphragm is obscured by aerated lung so must be looked at from below

Question 37

What should happen in the sniff test

Answer 37

On sniffing the normally innervated diaphragm contracts and moves sharply downwards (towards the feet, caudally)