Lung PoCUS Basics: Key Ultrasound Signs to Recognize

The SonoRAY post introduces these foundational lung ultrasound signs.

Shortness of breath? Start with the pleural line.

Unlike many other ultrasound examinations, lung PoCUS does not usually produce a direct image of the healthy lung tissue. Because air reflects and scatters ultrasound waves, clinicians interpret the movement, artifacts, and patterns generated at the pleural surface.

The Bat Sign

The bat sign helps confirm that the probe is positioned over the correct intercostal space. On the image, two adjacent ribs create acoustic shadows on either side of a bright horizontal pleural line.

Together, these structures resemble the wings and body of a bat. Once the bat sign is identified, evaluate the pleural line and the artifacts arising beneath it.

Lung Sliding

Lung sliding is the shimmering, side-to-side movement of the visceral pleura against the parietal pleura during respiration.

Its presence indicates that the pleural layers are touching at the location being scanned and therefore excludes pneumothorax at that specific point. However, absent lung sliding is not diagnostic by itself and may also occur with apnea, pleural adhesions, severe atelectasis, mainstem intubation, or other conditions.

A-Lines

A-lines are horizontal, regularly spaced reverberation artifacts located beneath the pleural line.

They represent aerated lung and are commonly seen in a normal lung examination. However, A-lines may also appear with conditions such as asthma, COPD, or pneumothorax, so they must be interpreted alongside lung sliding and the patient’s clinical presentation.

B-Lines

B-lines are bright vertical artifacts that:

• Originate at the pleural line
• Extend to the bottom of the image
• Move with lung sliding
• Erase the horizontal A-lines

A small number may occur in dependent areas of a normal lung. Multiple or coalescent B-lines indicate increased lung density or fluid but are not specific to a single diagnosis. Diffuse bilateral B-lines may support pulmonary edema, while focal B-lines may occur with pneumonia, pulmonary contusion, infarction, or other localized abnormalities.

Seashore and Barcode Signs

M-mode can help evaluate pleural movement. With normal lung sliding, the stationary chest wall creates horizontal lines above the pleura while the moving lung produces a granular appearance below it. This is known as the seashore sign.

When sliding is absent, parallel horizontal lines may appear above and below the pleural line. This is called the barcode or stratosphere sign. It supports absent pleural movement but is not specific for pneumothorax.

The Lung Point

The lung point is the transition between an area without lung sliding and an area where normal sliding returns during respiration. When identified in the appropriate clinical setting, it is highly specific for pneumothorax. Its location may also help estimate the extent of the pneumothorax, although it may not be visible when the pneumothorax is very large.

Additional Patterns

Lung PoCUS can also identify:

• Pleural effusion: fluid appearing above the diaphragm
• Consolidation: tissue-like or liver-like lung appearance
• Air bronchograms: bright branching structures within consolidated lung
• Irregular pleural lines: which may accompany focal or diffuse lung disease

These findings should be assessed across multiple lung zones rather than relying on a single image.

Lung PoCUS is a focused examination. Its findings should be combined with the history, physical examination, vital signs, cardiac ultrasound, laboratory results, and additional imaging when needed. Current international recommendations emphasize both its clinical value and its limitations as a standalone test. These principles are also important for clinicians pursuing a Resuscitation Ultrasound Course in Canada, where understanding how to integrate point-of-care ultrasound findings with the overall clinical picture is essential.

Find the bat sign.

Follow the pleural line.

Interpret the pattern—not one finding in isolation.