Lung Ultrasound: The Signs, the BLUE Protocol and the Right Machine
Air blocks ultrasound, so a lung scan reads artefacts as much as anatomy. The signs every lung scan is built on, how the BLUE protocol puts them together, and what to look for in the probe and settings.
The signs lung ultrasound reads
Start with the probe across two ribs in a longitudinal view: the rib shadows and the bright pleural line between them — the “bat sign” — orientate every view.
| Sign | What you see | What it suggests |
|---|---|---|
| Lung sliding | A shimmer along the pleural line with each breath | The two pleural layers are in contact; its absence raises the question of pneumothorax |
| Seashore and barcode signs | In M-mode, granular “sand” below the pleural line (seashore) or flat lines all the way down (barcode) | Sliding present, or absent, at that spot |
| Lung point | The place where sliding and no sliding alternate with breathing | A specific sign of pneumothorax |
| A-lines | Horizontal repeats of the pleural line at equal spacing | Air beneath the pleura — normal lung, or pneumothorax if sliding is absent |
| B-lines | Bright vertical lines from the pleural line to the bottom of the screen, moving with sliding | Three or more between two ribs is a B-pattern: fluid or thickening in the lung interstitium, as in pulmonary oedema, pneumonia or interstitial lung disease |
| Consolidation | Lung that looks like solid tissue, often with bright air bronchograms | Pneumonia or atelectasis; air bronchograms that move with breathing favour pneumonia |
| Pleural effusion | A dark space above the diaphragm, with the spine visible above it | Fluid; septations or debris suggest a complex effusion |
Read next Reverberation and other artefacts
The BLUE protocol in brief
The BLUE protocol (Bedside Lung Ultrasound in Emergency), published by Lichtenstein and Mezière in 2008, is a fast sequence for adults with acute respiratory failure. It checks set points on each side of the chest — the upper and lower BLUE points and the posterolateral PLAPS point — and adds a leg-vein scan, then sorts the findings into profiles. In the original ICU study the profiles matched the final diagnosis in about 90% of patients. It supports clinical judgement; it does not replace it.
| Profile | Findings | Points towards |
|---|---|---|
| A-profile with DVT | A-lines with sliding, plus a deep vein thrombosis | Pulmonary embolism |
| A-profile with PLAPS | A-lines with sliding, no DVT, consolidation or effusion at the PLAPS point | Pneumonia |
| Nude profile | A-lines with sliding, no DVT, no PLAPS | COPD or asthma |
| B-profile | B-lines on both sides of the anterior chest, with sliding | Cardiogenic pulmonary oedema |
| B′, A/B and C profiles | B-lines without sliding, B-lines on one side only, or anterior consolidation | Pneumonia |
| A′-profile with lung point | A-lines, no sliding and a lung point | Pneumothorax |
Read next Leg-vein compression scanningPOCUS equipment and training
Choosing a probe
Convex
A good all-round lung probe: deep enough for effusions, consolidation and the posterior points, with a usable view of the pleural line.
Phased array
Its small footprint fits between the ribs, and it is often already on the machine for cardiac POCUS, so one probe covers heart and lungs. The pleural line shows in less detail.
Linear
High frequency shows the pleural line and sliding in fine detail — useful for pneumothorax, pleural irregularities and children — but it does not see deep.
Micro-convex
A small curved footprint that fits between ribs with reasonable depth. Some lung ultrasound teachers use one probe of this type for everything, and it is common on neonatal and veterinary systems.
Read next Probe types and frequencies
Settings that help or hurt
- Use the lung preset if the system has one.
- Tissue harmonic imaging, compound imaging and speckle reduction are designed to suppress artefacts and can make B-lines look fewer or fainter. Many lung protocols scan with them off, or at least with the same settings every time.
- Put the focus at the pleural line when assessing sliding and B-lines.
- Use a short depth for the pleural line and more depth to look for effusion and consolidation.
- Use M-mode to document sliding as a seashore or barcode pattern.
- Save cine clips rather than still frames — sliding and B-lines are judged in motion.
- On a handheld, check that the frame rate shows sliding clearly and that the probe stays cool through a full multi-zone exam.
Read next Handhelds for lung and FASTHarmonics, focus and depth
Training, documentation and cleaning
Basic lung ultrasound is quick to learn but easy to over-read. The international evidence-based recommendations for point-of-care lung ultrasound (Volpicelli and colleagues, 2012) and their 2022 update set out the signs and their uses. Some units also grade each chest zone from 0 to 3 — from A-lines to consolidation — into a lung ultrasound score to follow a patient over time.
- Supervised scans and a log until each user is signed off for the questions they answer.
- Records of which zones were scanned and what was found in each, with clips saved to the patient record.
- A clear rule on which findings need formal imaging or a specialist review.
- Probe cleaning between every patient — lung scans move from bed to bed in emergency and ICU.
Read next Probe cleaning and disinfection
Related guides
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Frequently asked questions
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