Bedside lung ultrasound in emergency (approach)

Bedside lung ultrasound in emergency (BLUE) is a basic point-of-care ultrasound (POCUS) examination performed for undifferentiated respiratory failure at the bedside, immediately after the physical examination, and before echocardiography.

The protocol is simple and dichotomous, and takes fewer than 3 minutes to complete. It analyzes three standardized points on each hemithorax in patients with acute respiratory failure, seeking to establish the presence or absence of:

• lung sliding
• anterior lung rockets
• posterior and/or lateral alveolar and/or pleural syndrome (PLAPS)
• a noncompressible deep vein

Pathophysiologic “profiles,” based on standardized patterns of artifacts are then built, and a tentative pathophysiologic basis for the acute respiratory failure proposed. The chief aim of the protocol is to suggest a diagnosis with a target overall accuracy just over 90% (90.5%) with a simple, easy-to-purchase machine and a single, universal probe, without Doppler or other amenities.

Terminology

• the bat sign
  • cortices and posterior acoustic shadowing of the ribs are the wings, the hyperechoic "belly" being the pleural line
• A-lines
  • horizontal artifacts arising from the pleural line at regular intervals which are equal to the skin-pleural interface distance - indicating physiologic air (but also free air)
• B-lines
  • correlated with interstitial edema; they are defined according to seven criteria
    • comet-tail artifacts
    • arising from the pleural line
    • hyperechoic
    • laser beam-like
    • long, without fading
    • erasing A-lines
    • moving with lung sliding
• C-lines
  • centimetric in size, concave or curvilnear in shape, alveolar consolidation

Profiles

• A-profile: anterior lung-sliding with A-lines
• A'-profile: A-profile with abolished lung sliding
• B-profile: anterior lung-sliding with lung rockets
• B'-profile: B-profile with abolished lung sliding
• A/B-profile: unilateral B lines, contralateral A-lines 
• C-profile: any anterior lung consolidation (a thick, irregular pleural line is an equivalent)

Technique

• patient in supine position
• 3.5-5.0 MHz microconvex probe
• manually define anatomy: the operator's left (upper BLUE) hand and right (lower BLUE) hands, the upper placed in apposition to and parallel with the patient's clavicle, the tips of the digits touching the midline
  • the upper BLUE point is defined between the third and fourth digits of the upper BLUE hand, at their palmar insertion
  • the lower BLUE point corresponds to the middle of the palm of the lower BLUE hand

Findings

• anterior lung sliding (at bilateral upper BLUE points) is checked first, as its presence effectively rules out pneumothorax; anterior B lines are simultaneously sought (the B profile suggests pulmonary edema) 
• B , A/B, and C profiles suggest pneumonia
• A profile prompts a search for venous thrombosis, if present, pulmonary embolism is considered.
• If absent, PLAPS is sought - its presence (A profile plus PLAPS) suggests pneumonia; its absence suggests COPD/asthma

False negatives

• patients with COPD commonly show signs on ultrasound mimicking a pneumothorax 
• obesity
• subcutaneous emphysema
• lesions that do not reach the pleura.

False positives

• cardiogenic pulmonary edema and antibiotic therapy may result in pneumonia false positives

History and etymology

Dr Daniel Lichtenstein, French intensivist, designed the BLUE protocol.