lung normal
important: ultrasound cannot penetrate an air-filled lung, so we can not say a lung is normal.
we can exclude or suggest some pathologies with accuracy but cannot penetrate a lung enough to say it is normal.
limitations
- due to the physics of ultrasound, air filled structures cannot be penetrated by the ultrasound wave.
- therefore the internal architecture of a lung cannot be investigated with ultrasound if it is air-filled.
- however, the surface of the lung may give clues as to what lies beneath similarly to the surface of some water may be smooth, rippled, flowing or stationary and gives clues to the underlying material.
this image of a river is similar to a lung.
- if something reaches the surface (like the rock), you can examine it and assess it.
- there are turbulent areas showing that something beneath is irregular and ‘unhealthy’. you cannot tell what it is or how long it has been there without other information.
- the smooth surface hides anything that isnt coming close to the surface so we can’t examine what is in those depths.
- we can see if it is flowing (sliding) or not – which is important to know.
basic anatomy
pleura
- the lungs are surrounded by a pleural sac (membrane).
- this contains a tiny amount of pleural fluid (not visible).
- visceral pleura: the pleural surface closest to the lung.
- parietal pleura: the pleural surface closest to the ribs and chest wall.
- the lung should slide freely under the pleura.
lung
- right lung has 3 lobes
- left lung has 2 lobes
- the lobes are divided by fissures.
airways
from trachea to periphery-
- primary bronchi
- bronchi
- alveoli (the terminal sacs where gas exchange occurs)
basic lung and pleura anatomy.
ref: openstax college, cc by 3.0 <https://creativecommons.org/licenses/by/3.0>, via wikimedia commons
ultrasound lung at costal cartilage
m-mode for documenting pneumothorax
- a pneumothorax is diagnosed by abscence of the sliding pleura in a breathing patient.
- using m-mode simply is a way to document the finding.
- you will see on the images below that a stationary image looks the same regardless of prescence of a pneumothorax or not.
important: if the patient is not taking a reasonable breath, the lung will not slide giving a false positive for pneumothorax.
scan setup
role of ultrasound
- ultrasound can be used to evaluate the lung in a variety of clinical presentations. importantly the ultrasound findings should be put into context with the patient’s clinical
limitations
- shallow breathing
- poor probe/skin contact due to dressings, clothing, wounds.
patient preparation
- nil
equipment setup
preset
- lung preset if available.
otherwise
- curvilinear probe – abdominal preset
- linear probe – vascular preset
harmonics – off
compounding – off
depth – show at least 8cm of lung
far gain – higher than normal to be able to observe the lung artefacts
common pathology
- pneumothorax
- pleural effusion
- haemothorax
- collapse
- consolidation
- peripheral lung and pleural masses
ultrasound of the lung will also assist with diagnosis of:
- atelectasis
- pulmonary oedema
- pneumonia
pitfalls
- not being perpendicular to the pleura will cause loss of a smooth sliding lung surface and loss of a-lines. this may mimick pathology.
scanning technique
the scanning technique will vary based on the clinical question.
pneumothorax
scan sagittally across the rib spaces at the highest point on the chest realtive to the patient’s postition.
- supine – scan anteriorly.
- erect or semi erect – scan superiorly towards the apices.
- lateral decubitus – scan laterally (basal).
pleural fluid or basal consolidation
- scan the dependant most area in a sagittal or coronal plane.
generally this is posterolaterally.
generalised lung condition (oedema, atelectasis etc)
- follow a systematic protocol of examining both lungs thoroughly.
scanning protocols
- there have been many scanning protocols proposed in the literature.
- these are based on the clinical question.
- these are always evolving and are not used in isolation, but form part of the clinical assessment.
the more commonly used are below:
blue protocol
bedside lung ultrasound in emergency
- use of ultrasound in acute respitratory distress.
article on the blue protocol
falls protocol
fluid administration limited by lung sonography
- lung ultrasound in hemodynamic assessment of shock
ultrasound flow chart for the fals protocol
ref: falls-protocol: lung ultrasound in hemodynamic assessment of shock. dr daniel lichtenstein
article on the falls protocol
basic hardcopy imaging
- departmental policies should be followed.
- “informal ultrasound” does not preclude or over-rule policy and procedure,
- there are increasing requirements for documentation of bedside ultrasound findings with connection of equipment to pacs or cloud storage.
resources
dyspnoea
lung ultrasound in the critically ill – dr daniel lichtenstein
acute dyspnea in adults
acute dyspnea in pediatrics
references
web resources (not necesarily peer reviewed – but well recognised experienced educators)