Lung POCUS

Characteristics of the Normal or Fully Aerated Lung

• Lung sliding: The visible, respiration-dependent movement of the pleural line
• Smooth pleural line
• A-lines: Horizontal artifacts caused by the reflection of air at the tissue boundary. They appear at perfectly equal distances from one another. The distance between the pleural line and the first A line is exactly equal to the distance between the pleura and the transducer

Figure 2. A-lines demonstrated here. This represents an ideal image where the rib shadows are black, the pleural line is white and the soft tissue is grey.

- Set depth to 10cm and the focal point at the pleural line

Ultrasound Features of Lung Pathologies

Condition	Common Ultrasound Findings	Distribution / Behavior
Community-Acquired Pneumonia	Focal pleural-line abnormalities, multiple/confluent B lines (white lung), subpleural or lobular/segmental consolidations, air or fluid bronchograms.	Asymmetric and initially localized to specific lung areas.
Interstitial Pneumonia	Focal pleural-line abnormalities, multifocal B lines, white lung, multifocal subpleural consolidations.	Typically bilateral and inhomogeneous. Inflamed areas are often separated by fully aerated “spared areas”.
Pulmonary Edema	B lines that can progress to a white lung pattern.	Symmetric distribution, typically localized at the lowest points of the lungs due to gravity. Symmetric involvement of the 4 lower chest quadrants is pathognomonic for cardiogenic edema.
Pleural Effusion	Fluid collection in the pleural cavity. Relies on identifying the pleural cavity, diaphragm, and an abdominal organ (liver/spleen). The “spine sign” (visualizing the thoracic spine) indirectly indicates fluid.	Located at the lowest points due to gravity. Best assessed in a semirecumbent position. Can detect as little as 20 ml of fluid. Volume Estimation: $(\text{Diaphragm to lung base distance in cm}+\text{Chest wall to lung distance in cm})\times 70=\text{Volume in mL}$.
Pneumothorax	Absence of lung sliding, absence of B lines/subpleural lesions, and absence of the lung pulse. • Seashore sign: Normal M-mode (resembles sea and sand). • Stratosphere / Barcode sign: M-mode signature of absent lung sliding.	”Lung Point” is the only pathognomonic sign. It is the exact transient boundary where a healthy lung (with sliding) meets the pneumothorax (no sliding).
COPD & Asthma	Typically presents with completely normal lung ultrasound findings, acting as a diagnosis of exclusion.	Airway obstruction is diagnosed using M-mode to observe diaphragmatic kinetics (hyperechoic line rising on inspiration, falling on expiration). M-Mode Index of Obstruction: Ratio of excursion in the 1st second of forced expiration vs. total expiration. A value $<0.77$ indicates an obstructive pattern.
Pulmonary Embolism	Limited diagnostic value; primarily a diagnosis of exclusion. May occasionally reveal oval, round, or wedge-shaped consolidations.	The Vascular Sign: Characterized by blood flow that cuts off proximally within the consolidation on Doppler. (Distinguishes it from inflammatory consolidations where blood flow spans the entire structure) .

B-lines (interstitial Oedema)

• B-lines are thickening of the interlobular septum
• Appearance: Hyperechoic, laser-like vertical artifacts arising directly from the pleural line. They move in unison with lung sliding, travel all the way to the bottom of the screen, and erase A lines
• Clinical Significance: Healthy lungs may have 1–2 B lines per field. An increasing number signifies worsening edema. In severe cases, they merge to create a “white lung” pattern
  • Increase depth to differentiate true B lines from Z lines (short, ill-defined, clinically irrelevant artifacts)

• Artefacts that do not extend from the pleural line may be as a result of subpleural consolidation

Sea Shore Sign

• Shows that lung sliding is present

Barcode Sign

• Absence of lung sliding

Community Acquired Pneumonia Findings

• Focal pleural line abnormalities
• Multiple B-lines
• Multifocal confluent B-lines
• Subpleural consolidations
• Lobular or segmental consolidation
• Air or fluid consolidations

Interstitial Pneumonia Findings

• Focal pleural line abnormalities
• Multifocal B-lines
• Multifocal confluent B lines
• Subpleural consolidations

Pulmonary Oedema Findings

• B lines across lower 4 quadrants

Pleural Effusion Findings

• Observe at lowest point

Pneumothorax Findings

• Absence of lung sliding
• Absence of B lines or subpleural lesions
• Absence of lung pulse
• Presence of the lung point

RADiUS Exam

Figure 1. A fully aerated lung (Panel A) has a smooth and hyperechoic pleural line (down arrow) and horizontal artifacts called A lines (up arrows). Acoustic shadowing from the ribs can be seen (left- and right-facing arrows). A lung with edema (Panel B) has multiple vertical artifacts called B lines (left-facing arrows) and a normal pleural line (down arrow). A lung with consolidations (Panel C) has hypoechoic structures, which are formed by collapsed and airless alveoli (left-facing arrow) that are surrounded by aerated alveoli; the consolidations move together with lung sliding, which is movement of the pleural line (down arrow) in accordance with respiration. A lung with complete loss of aeration (Panel D) has lobular consolidation (left-facing arrow) and pleural effusion (down arrow)

# Sources - Buda, N., Mendrala, K., Skoczyński, S., Pasquier, M., Mazur, P., Garcia, E., Darocha, T., 2023. Basics of Point-of-Care Lung Ultrasonography. New England Journal of Medicine 389, e44. [https://doi.org/10.1056/NEJMvcm2108203](https://doi.org/10.1056/NEJMvcm2108203) - [Lung Ultrasound Explained (Point of Care, Bedside, Clinical) - YouTube](https://www.youtube.com/watch?v=_Q0cTG3ZlHk&list=TLPQMjMwNTIwMjbrZc6llVmp8A&index=3)