Predicting the difficult airway

Difficult to Bag Ventilate

Difficult BVM (MOANS)

  • Mask seal
  • Obesity
  • Aged
  • No teeth
  • Stiffness (resistance to ventilation)

Difficult to Intubate

A grade 3 on the upper lip bite test (patient unable to bite upper lip with lower teeth) has LR+ 14 for predicting difficult intubation[1]


An airway assessment score based on criteria of the LEMON method is able to successfully stratify the risk of intubation difficulty in the emergency department.[2]


  • Look at the patient externally for characteristics that are known to cause difficult laryngoscopy, intubation or ventilation[3]
  • Trauma
  • Short neck
  • Micrognathia
  • Prior surgery
  • May also be difficult to bag
    • Body mass index
    • Advanced age
    • Beard
    • No teeth
    • Snoring
    • Dentures

Evaluate 3-3-2-1

3-3-2 ruleDistance between patient's incisor teeth of 3 finger breadths and distance between the thyroid notch and the floor of the mouth should be at least 2 finger widths
  • 3 - Ideally the distance between the patient's incisor teeth should be at least 3 finger breadths
  • 3 - Distance between the hyoid bone and the chin should be at least 3 finger breadths
  • 2 - Distance between the thyroid notch and the floor of the mouth should be at least 2 finger breadths
  • 1 - Lower jaw should not sublux more than 1cm


Mallampati Score
  • The patient sits upright, opens mouth and protrudes tongue
  • Grades are based on visibility of the uvula, posterior pharynx, hard, and soft palate


Neck Mobility

  • Patient places chin down onto their chest and extend their neck.
  • Remove the hard collar and provide manual stabilization in trauma patients.
  • Poor neck mobility impacts ability to have airway access alignment.

See Also

Airway Pages


  1. Detsky ME, Jivraj N, Adhikari NK, et al. Will This Patient Be Difficult to Intubate?: The Rational Clinical Examination Systematic Review. JAMA. 2019;321(5):493-503.
  2. Reed, M. et al. Can an airway assessment score predict difficulty at intubation in the emergency department? Emerg Med J. 2005 Feb; 22(2): 99–102. doi: 10.1136/emj.2003.008771
  3. Rennie LM, Dunn MJG, et al. Is the ‘LEMON’ method an easily applied emergency airway assessment tool? European Journal of Emergency Medicine 2004;11:154–7