Difficult airway algorithm

LEMON Mnemonic

  • 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.[1]


  • Look at the patient externally for characteristics that are known to cause difficult laryngoscopy, intubation or ventilation[2]
  • 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 - 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


  • 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.
Mallampati Score
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

ASA Difficult Airway Algorithm

  • Does not necessary apply to the ED since the patient can always be awakened and case cancelled
    • Cricothyrotomy should always be the last step in patients with failure to oxygen and ventilate with BVM and inability to intubate
    • Straight blade- Miller- may offer better manipulation of a large epiglottis in children or for micrognathia or "buck teeth"

Airway Adjuncts

Endotracheal tube introducer (ETI)/Gum Elastic Bougie

  • Higher first pass success when used with direct laryngscope vs. styletted ET tube regardless of whether difficult airway was expected or not [3]
  • Blind orotracheal intubation

Blind Naso Trach Intubation

  • Not as successful but still an option
  • Higher complication rate - bleeding, emesis, and airway trauma

Lighted Optical Stylets

  • High success rate - especially good for trauma, c-spine precautions
  • Use for both reg and nasotrach
  • Lower complication rate
  • Limited by fogging, secretion, recognition of anatomy, cost, and rare provider experience


  • Can use without muscle relaxants
  • Better than face mask
  • Can be used as bridge to fiberoptic intubation
  • Limited by unreliable seal at peak insp pressure
  • Aspiration risk
  • Mucosal trauma
  • LMA better than endotracheal for paramedics, especially in pediatric patients[4][5]
  • Intubating LMA (LMA-Fastrach) provides the opportunity to convert to a definitive airway after rescue with the supraglottic device

Combitube- esoph obturator

  • Good for nurses and paramedics with limited intubation skill
  • Indicated if difficult airway predicted: cannot see glottis with laryngoscope
  • Reduced risk for aspiration compared to face mask or LMA
  • Can maintain spinal immobilization
  • Large size predisposes to esophogeal dilatation and laceration as a complication

Percutaneous Transtracheal Ventilation

  • PTV
  • Prefered over crithyrotomy in children up to age 10-12
  • Needle, 16-18ga through cricoid membrane, connected to 50 psi 02[6]
    • Oxygenates well
    • Ventilate through glottis and upper airway - can retain CO2
  • Need adequate oxygen pressure
  • 1 sec insp and 2- 3 sec exp to avoid breath stacking
  • Can use for 30-45 min
  • May cause pneumothorax or barotrauma
  • Contraindications
    • Distorted anatomy
    • Bleeding diathesis
    • Complete airway obstruction

Retrograde Intubation

  • Percutaneous guide wire through cricoid and retrograde intubation over wire
  • Use guide catheter over wire and then ett
  • Need time to set up
  • Risk hematoma, pneumothorax
  • Contraindicated
    • Bleeding
    • Distorted anatomy

Fiberoptic Bronchoscopic Intubation

  • Takes time to set up
  • Good for c-spine injury or awake patient with diff airway
  • Go through nose
  • Use for all ages, can give 02 during procedure thru fiberscope, immediate confirmation of position
  • Limited by secretions, bleeding, poor suction,

Rigid Fiberoptic Laryngoscopes

  • Use for diff airway or spinal immobolization
  • Not as good and longer time to intubate than flex scope

Improving Passive Oxygenation

  • Use in overweight, poor O2 reserve, hypoxia at baseline, concerns for rapid progression to hypoxia once apnea
  • Pre-oxygenate while sitting upright, only lay back once RSI drugs pushed.
  • 30 degrees reverse trendelenburg position for intubation
  • Nasal O2 while pre oxygenating and DURING intubation (after induction increase to 15L)

Surgical Airway

  • Can get subglottic stenosis
  • Rapid 4 step procedure faster but higher complication rate - cric cart fx
  • Can also do wire guided
  • Long term morbid, mortality similar to tracheostomy

See Also



  1. 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
  2. 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
  3. Driver, B. E., Prekker, M. E., Klein, L. R., Reardon, R. F., Miner, J. R., Fagerstrom, E. T., … Cole, J. B. (2018). Effect of Use of a Bougie vs Endotracheal Tube and Stylet on First-Attempt Intubation Success Among Patients With Difficult Airways Undergoing Emergency Intubation: A Randomized Clinical Trial. JAMA: The Journal of the American Medical Association, 319(21), 2179–2189.
  4. Zhu X-Y, Lin B-C, Zhang Q-S, Ye H-M, Yu R-J. A prospective evaluation of the efficacy of the laryngeal mask airway during neonatal resuscitation. Resuscitation. 2011;82(11):1405–1409. doi:10.1016/j.resuscitation.2011.06.010
  5. Calkins MD, Robinson TD. Combat trauma airway management: endotracheal intubation versus laryngeal mask airway versus combitube use by Navy SEAL and Reconnaissance combat corpsmen. J Trauma. 1999;46(5):927–932
  6. Beck, E., Kharasch, M., Casey, J., Ochoa, P., Menon, S., Calabrese, N. and Wang, E. (2011) ‘Percutaneous Transtracheal jet ventilation’, Academic Emergency Medicine, 18(5), pp. e38–e38.