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Lung ultrasound answers, at the bedside and in minutes, the question that most often decides a respiratory treatment: is this consolidation, collapse, effusion or oedema? For several of those it is more accurate than both auscultation and the portable chest X-ray. It is operator-dependent, requires formal training, and in Australia sits behind credentialing for physiotherapists — but understanding the images is useful whether or not you hold the probe.
What you are actually looking at
Ultrasound cannot penetrate air, so normal lung produces no image at all — what is seen are artefacts generated at the pleural line, and those artefacts are the diagnostic information. As air is replaced by fluid or tissue, the lung becomes progressively more visible. That single principle explains every sign below.
The core signs
| Sign | Appearance | Means |
|---|---|---|
| Lung sliding | Shimmering movement of the pleural line with respiration | Visceral and parietal pleura in contact and moving — effectively excludes pneumothorax at that point1 |
| A-lines | Horizontal repeating echoes below the pleural line | Normal, aerated lung — or, if sliding is absent, pneumothorax |
| B-lines | Vertical “comet tail” artefacts to the bottom of the screen, moving with sliding | Interstitial syndrome. Three or more in one view is abnormal; bilateral and diffuse suggests cardiogenic pulmonary oedema1 |
| Consolidation | Tissue-like (“hepatised”) lung, often with air bronchograms | Alveolar filling — pneumonia, atelectasis or contusion, distinguished by the bronchogram behaviour below |
| Pleural effusion | Anechoic space above the diaphragm, spine visible beyond it | Fluid — quantifiable and directly markable for drainage |
| Lung point | The exact point where sliding starts and stops within one view | Specific for pneumothorax and marks its edge1 |
The distinction that changes physiotherapy
Consolidated lung looks similar whether it is infected or collapsed. The differentiator is the air bronchogram:
- Dynamic air bronchograms — bronchograms that move with respiration — indicate patent airways, and therefore pneumonia rather than resorptive collapse. Airway clearance will not re-expand it, and may be futile.
- Static air bronchograms, or their absence with volume loss and a shifted mediastinum, suggest obstructive atelectasis — the situation in which secretion clearance and recruitment are indicated.
This is precisely the question auscultation cannot answer, and the one on which a portable chest X-ray is often equivocal. A systematic review in Journal of Physiotherapy found lung ultrasound more accurate than conventional respiratory assessment for pleural effusion, consolidation and collapse.2
How it compares
| Finding | Lung ultrasound | Portable chest X-ray |
|---|---|---|
| Pneumothorax | High sensitivity, markedly better than supine radiography3 | Poor when supine — air collects anteriorly and is easily missed |
| Pleural effusion | Highly accurate; volume estimated and site marked1,2 | Insensitive to small effusions; supine films mislead |
| Consolidation / collapse | Accurate, and distinguishes the two2 | Frequently cannot separate them |
| Interstitial oedema | B-line pattern is sensitive and appears early1,4 | Later and less sensitive |
| Radiation | None — repeatable as often as needed | Cumulative dose, and a wait for the film |
The BLUE protocol
Lichtenstein's BLUE protocol applies a small number of standard points to acute respiratory failure and reaches a diagnosis in around three minutes with high accuracy.4 The value for physiotherapy is not the algorithm itself so much as its discipline: scan the same points, in the same order, every time, comparing left with right, so that serial scans are comparable and change is real rather than an artefact of where the probe was placed.
Diaphragm ultrasound
The same machine assesses the diaphragm directly, which is otherwise almost invisible to clinical examination.
- Thickness and thickening fraction at the zone of apposition — a measure of contractile effort, used to detect ventilator-induced diaphragm dysfunction and to inform weaning.5
- Excursion in the subcostal view — useful for suspected phrenic nerve injury after cardiac or thoracic surgery, and for unilateral paralysis.
Both give an objective number where the alternative is inference, and both can be repeated daily without dose.
Scope, training and governance
Practical limits worth knowing regardless: it is blind to anything surrounded by aerated lung, degraded by subcutaneous emphysema and surgical dressings, difficult over large body habitus, and unable to see the mediastinum. It complements the chest X-ray and CT rather than replacing either.
What this means for physiotherapy
- It answers “will clearance help this?” more reliably than any bedside test we have used historically.
- It gives an objective, repeatable measure for re-expansion — treatment effect rather than treatment delivered.
- Understanding the images is worthwhile even without credentialing: it changes how you read the radiologist's report and how you argue for or against an intervention on a ward round.
- If a service intends to use it, the governance conversation comes first, not after the probe arrives.
References & evidence base
- Volpicelli G, Elbarbary M, Blaivas M, et al. International evidence-based recommendations for point-of-care lung ultrasound. Intensive Care Med. 2012;38(4):577–591.
- Hansell L, Milross M, Delaney A, Tian DH, Ntoumenopoulos G. Lung ultrasound has greater accuracy than conventional respiratory assessment tools for the diagnosis of pleural effusion, lung consolidation and collapse: a systematic review. J Physiother. 2021;67(1):41–48.
- Alrajab S, Youssef AM, Akkus NI, Caldito G. Pleural ultrasonography versus chest radiography for the diagnosis of pneumothorax: review of the literature and meta-analysis. Crit Care. 2013;17(5):R208.
- Lichtenstein DA, Mezière GA. Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE protocol. Chest. 2008;134(1):117–125.
- Goligher EC, Laghi F, Detsky ME, et al. Measuring diaphragm thickness with ultrasound in mechanically ventilated patients: feasibility, reproducibility and validity. Intensive Care Med. 2015;41(4):642–649.
- Le Neindre A, Mongodi S, Philippart F, Bouhemad B. Thoracic ultrasound: potential new tool for physiotherapists in respiratory management. A narrative review. J Crit Care. 2016;31(1):101–109.
- Australasian Society for Ultrasound in Medicine. Standards of Practice. Sydney: ASUM; 2024.
References are numbered in citation order (Vancouver/BMJ style) and were current at the time of writing. Guidelines are living documents — verify against the latest version before clinical use.
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