Ultrasound - Lung

Indications

To assess and exclude or confirm the presence of:

Pneumothorax

Pleural fluid

Interstitial lung fluid (heart failure)

Consolidation (pneumonia or atelectasis)

Consider in the following presentations:

Dyspnoea

Chest pain

Trauma

Contraindications (absolute in bold)

Tension pneumothorax requiring emergency decompression

Alternatives

Chest X-ray

CT scan

Informed consent

Medical emergency

Consent is not required if the patient lacks capacity or is unable to consent

Brief verbal discussion is recommended if the situation allows

or

Verbal consent

Less complex non-emergency procedure with low risk of complications

Potential complications

Failure to visualise structures (excess tissue, gas in tissue, pain)

Failure of image interpretation (false negative or positive)

Procedural hygiene

Standard precautions

PPE: non-sterile gloves

Area

Any bed

Staff

Procedural clinician

Equipment

Towel

Ultrasound machine and gel

Linear ultrasound probe (focused at pleural line)

Phased array ultrasound probe or curvilinear ultrasound probe (depth set to 15cm)

Positioning

Semi-recumbent or supine (trauma)

Scanning (pneumothorax)

Place linear probe longitudinally at the midclavicular just inferior to the clavicle

Identify the pleural line beneath the ribs

Evaluate for pleural sliding, shimmering (indicating pleural opposition)

Reassess proximally and distally

Consider using M-mode evaluation over time (seashore sign excludes pneumothorax)

Scanning (pleural effusion)

Select phased array ultrasound probe or curvilinear ultrasound probe (depth set to 15cm)

Oblique placement between ribs 8-11 at right mid-axillary line (marker to patient’s head)

Identify kidney, liver and diaphragm then rock probe to evaluate above the diaphragm

Oblique placement between ribs 6-9 at left posterior axillary line (marker to patient’s head)

Identify spleen, liver and diaphragm then rock probe to evaluate above the diaphragm

Free fluid in the hemithorax will be identified as an anechoic area above the diaphragm

If an effusion is seen, assess for consolidated lung visualised within a large effusion

If no fluid is seen, look for mirror image artefact and the spine sign to exclude pleural fluids (see below)

Scanning (interstitial lung fluid and pneumonia)

Select the phased array ultrasound probe with depth set to 15cm (or curvilinear ultrasound probe)

Using the anterior axillary line and the nipple line, divide each hemithorax into four zones

Orienting the transducer longitudinally in each zone identify two ribs and the pleural line beneath

Assess for multiple B lines indicating interstitial fluid (reverberation artefacts extending to the far field)

Assess for hepatisation of the lung indicating consolidation (lung appears similar to the liver)

Post-procedure care

Clean ultrasound gel from patient

Initiate further management if required

Document (indication, structures identified, interpretation)

Tips

Avoid confusing movement of the pericardium with pleural sliding in the left chest

Anterior two regions scan can exclude severe interstitial syndrome or pneumothorax in the critically ill

Subtle pathology requires multiple scanning positions (early pneumonia, apical pneumothorax or mild CCF)

Use lung pre-set (or turn off filter settings and image enhancing features) when looking for B lines

Discussion

Pleural opposition excludes pneumothorax and can be confirmed by observing sliding or shimmering of the visceral on parietal pleura. The absence of pleural sliding is not 100% specific for pneumothorax. Other causes include immobility of the pleural or lung in conditions such as pleurodesis, pleural scarring, lung contusions, bronchial obstruction, and advanced bullous emphysema. Comet tails (reverberation artefact similar to B lines) and B lines (see below) also help confirm the absence of pneumothorax.

When scanning for pleural effusions, free fluid in the hemithorax is confirmed by anechoic area above the diaphragm. If this is not present pleural fluid is excluded by confirming a mirror image artefact of the diaphragm and the loss of visualisation of the spine and vertebral bodies during inspiration (spine sign). Both features demonstrate that the thoracic cavity is full of air.

If there is fluid in the interstitial tissue the lung begins to reflect ultrasound waves which would normally be scattered. This is seen as vertical, bright, torch like white ‘B lines’ which originate at the pleura and are transmitted the full length of the screen. These B lines move back and forth with respiration as the pleura move. A normal lung may have occasional B lines (maximum three on screen in any window), but increased B lines indicates increased pleural fluid. As interstitial fluid increases to severe levels, these lines start to coalesce and become wedge-shaped. Bilateral extensive B lines suggest volume overload, heart failure or acute respiratory distress syndrome. Unilateral or localised B lines suggest focal pneumonitis which may progress to lung consolidation, demonstrated by increased lung density and the appearance of lung changing to that of liver (hepatisation).

Peer review

This guideline has been reviewed and approved by the following expert groups:

Emergency Care Institute

Please direct feedback for this procedure to ACI-ECIs@health.nsw.gov.au.

References

Roberts JR, Custalow CB, Thomsen TW. Roberts and Hedges’ clinical procedures in emergency medicine and acute care. 7th ed. Philadelphia, PA: Elsevier; 2019.

Dunn RJ, Borland M, O’Brien D (eds.). The emergency medicine manual. Online ed. Tennyson, SA: Venom Publishing; 2019.

Mayo P. Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax. In: UpToDate. Waltham (MA): UpToDate. 2020 Feb 5. Available from: https://www.uptodate.com/contents/bedside-pleural-ultrasonography-equipment-technique-and-the-identification-of-pleural-effusion-and-pneumothorax

Emergency ultrasound imaging criteria compendium. Ann Emerg Med. 2016;68(1):e11-e48. doi:10.1016/j.annemergmed.2016.04.028

Dawson M, Mallin M. Introduction to bedside ultrasound: volume 1. New York NY: Apple Books; 2013.

Dawson M, Mallin M. Introduction to bedside ultrasound: volume 2. New York NY: Apple Books; 2013.

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