Thoracic ultrasound — pleural assessment and site marking
Both hemithoraces where the question is bilateral, otherwise the symptomatic side: costophrenic recess, the full craniocaudal extent of any collection, the diaphragm and the underlying lung and, where a drain is planned, the intended intercostal space with the patient in the position they will occupy for the procedure.
Typical, not policy
Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.
When to use it
- Characterisation of a pleural effusion seen on a chest radiograph or CT — anechoic and free-flowing versus complex septated versus echogenic.
- Site marking immediately before pleural aspiration or intercostal drain insertion.
- Distinguishing an effusion from consolidation, collapse or pleural thickening where the radiograph shows only a white hemithorax.
- Suspected pneumothorax at the bedside where the patient cannot be sat up for an erect film.
- Serial assessment of a known effusion, where repeated radiographs would otherwise be requested.
Technique
- A curvilinear probe surveys the collection and the diaphragm; a linear high-frequency probe interrogates the pleural line, septations and any pleural thickening or nodularity.
- Both the depth to the pleura and the depth to the underlying lung or diaphragm should be recorded, not just the presence of fluid — the safe needle depth is the deliverable.
- Colour Doppler and the "fluid colour sign" help confirm that an echogenic, apparently solid-looking collection is in fact drainable fluid.
- Septation is far better shown by ultrasound than by CT, and its presence changes management towards a larger drain and intrapleural agents rather than simple aspiration.
Where it goes wrong
- Marking a site with the patient in one position and then draining in another is the classic mechanism of injury — the mark must be made in the procedural position and used immediately.
- An X marked on the skin without a recorded depth invites a needle that is too long or too short; the depth measurement is part of the study.
- An echogenic empyema or a haemothorax can look solid and be mistaken for consolidation, leading to a drainable collection being left alone.
- Ultrasound does not exclude an underlying mass or malignancy — a unilateral effusion still needs cross-sectional imaging for the cause.
- A high-riding diaphragm, sub-diaphragmatic viscera and an elevated hemidiaphragm from phrenic palsy are all mistaken for pleural fluid if the diaphragm is not positively identified.
Contrast
None
Acquisition
- Breathing
- Quiet tidal breathing, with a dynamic sweep through the respiratory cycle so that diaphragmatic movement and lung sliding are seen.
- Preparation
- The patient must be able to sit forward for a posterior approach; state if they can only be scanned supine, because that changes the achievable drainage site. Where the study is to mark a site, it should be performed by, or immediately before, the operator who will do the procedure — a mark made hours earlier on a different posture is not a safe mark.