Indications

• Identify acute pneumothorax (highly sensitive)
• Identify abnormal collections of pleural fluid
  • Pulmonary edema
  • Consolidation
  • Pleural effusion
• Part of extended FAST exam in case of trauma

Contraindication

• Known tension pneumothorax requiring immediate intervention

Limitations/pitfalls

• Morbid obesity can limit adequacy of image
• Absence of pleural sliding is not 100% specific for pneumothorax, as prior pleurodesis, pleural scarring, lung contusions, bronchial obstruction, and advanced bullous emphysema, may result in absence of lung sliding
• Presence of lung sliding only excludes pneumothorax immediate under the transducer

Technique

• Linear probe for lung sliding
• Curvilinear probe for B-lines and effusion
• Set the ultrasound machine to “lung” preset
• Indicator always toward the head
• Obtain clips in multiple locations, especially for lung sliding
• Always label left or right

Pathology

Pneumothorax

• In a trauma patient on his/her back, the anterior chest will be the most sensitive area to identify a pneumothorax
• Using a linear probe, the transducer is placed in the mid-clavicular line, immediately inferior to the clavicles, and the orientation marker is directed cephalad in a sagittal plane
• Identify
  • Two ribs, with distal shadowing
  • The pleural line beneath the ribs 

 

• Findings that exclude pneumothorax
  • pleural sliding (lung slide) or shimmering as the patient breathes, indicating that the lung is expanded with the visceral and parietal pleura directly apposed. 
  • “lung pulse” (motion of visceral pleura and lung in time with cardiac motion)
  • presence of B-lines (see below)
• The absence of any of these findings is highly suggestive of the presence of a pneumothorax, although not 100% specific
• Each interspace in the mid-clavicular line should be systematically evaluated to the level of the diaphragm on both sides
• Repeat the above examination of the lateral chest by scanning down each interspace along the midaxillary line, and of the posterior thorax along each interspace on the patient’s back 
• In critical situations, the evaluation may be limited to a single location on each anterior hemothorax. This two-point exam may identify large pnemothoraces, but miss a smaller pneumothorax. 
• The presence of the “lung point” sign is pathognomonic of the presence of pneumothorax
  • the point where the visceral pleura (lung) begins to separate from the parietal pleural (chest wall) at the margin of a pneumothorax
  • Visualized as lung sliding coming in and out of the view with each breath on ultrasound

 

• M mode
  • The M-mode sampling bar is placed in the middle of the intercostal space and the resulting M-Mode tracing is evaluated over time. 

 

• In the normal patient a linear pattern superficial to the pleural line is in sharp distinction to the granular pattern deep to it (the “seashore sign”)

 

• With pneumothorax, there is a horizontal linear pattern above and below the pleural line (“stratosphere sign” or “barcode sign”) 

Pleural effusion


Right lung base effusion:

• Curvilinear probe is placed in an intercostal space around the mid-axillary line at the level of the nipple line, with the orientation marker directed cephalad. 
• Identify the kidney, liver, and diaphragm, then angle or rock the probe to evaluate above the diaphragm
• Free fluid in the hemithorax will be identified as an anechoic or black area above the diaphragm. 
• Presence of the “spine sign” highly indicative of pleural effusion
  • the visualization of the vertebral bodies  in the thoracic cavity above the diaphragm which are usually not seen unless there is a fluid collection

Left lung base effusion

• repeat the above steps following the identification of the spleen, kidney, and diaphragm 

Interstitial Lung Fluid

• using the curvilinear probe, scan along the anterior, posterior, lateral, superior, and inferior chest walls with the orientation marker directed cephalad
• the presence of widespread B-lines is indicative of accumulation of fluid within the pulmonary interstitium
  • these are fine reverberation artifacts that extend from the pleural line to the far field
  • more than 3 B-lines per rib space = interstitial fluid

 

• this needs to be differentiated from A-lines, which are normal reverb artifacts
  • a lines are horizontal, echogenic long path reverberation artifacts that occur beneath the pleural line at multiples of the distance between the ultrasound probe and pleura
  • results from sound reflecting between two parallel, closely apposed reflective surfaces

References
https://www.yale.edu/imaging/echo_atlas/contents/index.html
https://radiopaedia.org/articles/thoracic-spine-sign-ultrasound?lang=us
    

Author
Alek Rosenthal, MD