POCUS and critical care echo

Lung ultrasound and the BLUE protocol

Reviewed Nov 2026·2 references
New· views rounded down, updated weekly

Lung sliding, A-lines, B-lines, consolidation and effusion answer most bedside questions: pneumothorax, pulmonary oedema vs COPD/asthma, pneumonia, PE and pleural effusion.

At the bedside

Timed steps
  1. 1

    Probe and points

    Set up

    Linear (pleura) or curvilinear/phased (deeper). BLUE points: upper and lower anterior, and PLAPS point (posterolateral) on each side.

  2. 2

    Signs

    Pneumothorax

    Absent lung sliding + no B-lines + no lung pulse; lung point is specific (diagnostic). Presence of sliding or B-lines rules out pneumothorax at that point.

  3. 3

    B-lines

    Interstitial syndrome

    ≥ 3 B-lines per intercostal space; bilateral diffuse = pulmonary oedema or ARDS/interstitial disease; focal = pneumonia, contusion.

  4. 4

    Tissue pattern

    Consolidation

    Hepatisation, shred sign; dynamic air bronchograms suggest pneumonia rather than resorptive atelectasis.

  5. 5

    Anechoic space above diaphragm

    Effusion

    Spine sign, plankton sign; septations or echogenic fluid suggest exudate/empyema. Estimate volume and mark the site for drainage.

  6. 6

    Profiles

    BLUE

    A-profile + DVT = PE; A-profile + no DVT + PLAPS = pneumonia; A-profile without = COPD/asthma; B-profile = pulmonary oedema; A' profile + lung point = pneumothorax; B' / A/B / C profiles = pneumonia.

BLUE protocol profiles

ProfileFindingsLikely diagnosis
A-profileSliding + A-lines anteriorlyWith DVT: PE; with PLAPS: pneumonia; neither: COPD/asthma
B-profileSliding + bilateral anterior B-linesHaemodynamic pulmonary oedema
B'-profileAbolished sliding + B-linesPneumonia
A/B-profileB-lines one side, A-lines otherPneumonia
C-profileAnterior consolidationPneumonia
A'-profileAbolished sliding + A-linesPneumothorax if lung point present
Red flag · call your senior now
Absent sliding + lung point in a hypotensive ventilated patient: decompress.
Pitfall
Absent sliding also occurs with mainstem intubation, apnoea, pleurodesis and large bullae.
Pitfall
B-lines are not specific to pulmonary oedema (also ARDS, fibrosis, pneumonia).
Pearl
Lung ultrasound beats supine chest X-ray for pneumothorax, effusion and consolidation.

References

  1. 1

    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

  2. 2

    Lichtenstein DA, Mezière GA. Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE protocol. Chest. 2008;134(1):117-125

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