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.

It has been designed as a fast (<3 minute), three-point examination for severely dyspnoeic patients bound for the Intensive Care Unit. Pathophysiologic “profiles,” based on standardised patterns of artifacts ("A" or "B lines"), the presence or abolition of lung sliding, and the presence/absence of alveolar consolidation are considered for six diseases which account for 97% of patients in the emergency department.

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

• bat sign: used to find the pleural line, i.e. if one recognizes the ribs as the "wings" then the bat's ''belly'' is the pleural interface
• 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 oedema; 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: alveolar consolidation abutting the pleural line

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 middle of the upper BLUE hand demarcates one’s initial probe placement, the (lower BLUE) corresponds to the middle of the palm of the lower 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 oedema) 
• 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

• Patientspatients with COPD commonly show signs on ultrasound mimicking a pneumothorax^7,8 
• obesity
• subcutaneous emphysema
• lesions that do not reach the pleura.

False positives

• cardiogenic pulmonary oedema and antibiotic therapy may result in pneumonia false positives ¹

History and etymology

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