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Lung Ultrasound

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


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 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
    


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  • Home
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  • D-loads & Guides
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    • Intern Rotation
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  • Modules
    • Pulmonary >
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      • Early Pregnancy
    • DRAUP
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      • PIV's
  • Wash U Blog
  • Wash U Qpath
    • GO TO QPATH
    • QPATH Workflow