Ultrasound Teaching Atlas
Draft — not yet peer-reviewedcoreThorax / PleuraBLUE

Lung — Anterior (BLUE Protocol)

Assess the anterior pleura for lung sliding, A-lines, and B-lines — and rule pneumothorax in or out.

This module is a content/teaching-structure draft. Images shown are illustrative schematics — real, de-identified, license-verified ultrasound clips replace them before peer review.

Learning objectives

  • Identify the pleural line using the 'bat sign'.
  • Distinguish lung sliding from its absence (seashore vs. barcode on M-mode).
  • Differentiate A-lines (normal/air) from B-lines (interstitial syndrome).
  • Recognize the lung point as specific for pneumothorax.

Maps to

  • Resident: ACEP Emergency Ultrasound — Thoracic: Image Acquisition
  • Resident: ACEP Emergency Ultrasound — Thoracic: Pneumothorax & B-lines
  • Tech: Critical care / POCUS lung assessment

Acquisition — getting the view

Probe
linear
Patient position
Supine; the most non-dependent point is the anterior chest.
Orientation convention
radiology
Probe placement
Anterior chest, ~2nd–3rd intercostal space, midclavicular line
Marker direction
Indicator cephalad (longitudinal, across two ribs)

Probe placement (3D)

Anterior chest, ~2nd–3rd intercostal space, midclavicular line

Structures in the imaging plane (near → far): Chest wall / soft tissue · Ribs (with shadows — 'bat sign') · Pleural line · Lung surface (A-lines / B-lines arise here)

Step by step

  1. Place the linear probe longitudinally over two ribs in the upper anterior chest, indicator cephalad.
    Why: Two rib shadows plus the pleural line between them form the 'bat sign'.
  2. Identify the bright pleural line and watch for shimmering lung sliding.
    Why: Sliding present at a spot rules out pneumothorax there.
  3. If sliding is uncertain, use M-mode: seashore sign (normal) vs. barcode sign (no sliding).
    Why: M-mode objectively captures the presence or absence of sliding.

Troubleshooting

Cannot tell if lung is sliding.
Use M-mode through the pleural line, or look for B-lines/lung pulse which also exclude pneumothorax at that spot.
Absent sliding but unsure of pneumothorax.
Search laterally for the lung point — the transition from sliding to no sliding — which is specific for pneumothorax.

Findings: normal

Normal aerated lung

Bat sign with a sliding pleural line and horizontal A-lines; M-mode shows the seashore sign.

Signs: Lung sliding present; A-lines (horizontal reverberation); Seashore sign on M-mode

Schematic of normal lung with bat sign and A-lines
Schematic: bat sign, pleural line, and A-lines.
Original schematic, dedicated to the public domain (CC0).

Findings: pathology

Pneumothorax

Absent lung sliding with A-lines and no B-lines; M-mode shows the barcode sign. The lung point confirms it.

Signs: Absent sliding; Barcode/stratosphere sign on M-mode; Lung point (specific)

Schematic M-mode barcode sign of pneumothorax
Schematic: barcode sign — absent lung sliding.
Original schematic, dedicated to the public domain (CC0).

Interstitial syndrome (B-lines)

Three or more vertical, laser-like B-lines in a field arising from the pleural line indicate interstitial fluid (e.g., pulmonary edema).

Signs: ≥ 3 B-lines per field; B-lines erase A-lines and move with sliding

Interpretation practice

On M-mode through the anterior pleura you see uniform horizontal lines with no granular 'sand' below the pleural line. What is this?

M-mode barcode pattern
Uniform horizontal lines on M-mode — interpret.
Original schematic, dedicated to the public domain (CC0).

Check your understanding

Which finding is the most specific for pneumothorax?

What do three or more B-lines in a field indicate?

References

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