Question 3

Outline how you would assess a patient for potential difficulty with endotracheal intubation.

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College Answer

•    History: of previous difficulty with intubation, infections/swelling affecting mouth or neck, problems with mouth opening or neck movement (arthritis, cervical spine injury), problems with teeth (especially caps/crowns, law wiring etc.).
•    Examination (multiple components) consider:
o teeth (maxillary anterior to mandibular; length of upper incisors; ability to prognath mandible; inter-incisor distance [need > 3 cm])
o Pharynx (ability of visualise uvula and tonsillar pillars; height and narrowness of palate).
o Mandibular space (thyromental distance 2: 3 fingerbreadths [6 cm]; compliance and distensibility of submandibular space).
o Length of neck (qualitative: short neck more difficult eg. syndromes).
o Thickness of neck (qualitative: thick neck decreases ability to align planes).
o Range of motion (of head and neck: eg. sniffing position)
•    Consider also the ability to assess potential difficulties by actually having a look with a laryngoscope.


This question was recycled as Question 11 in the first paper of 2006. To simplify revision, the answer to that SAQ is reproduced below.

Anaesthetic history:

  • History of difficult intubation in previous attempts
  • History of airway-altering changes since the last anaesthetic, eg. significant weight gain, C-spine surgery, head and neck radiotherapy, etc.

Patient characteristics:

  • Obesity
  • Obstructive sleep apnea
  • History of snoring

Specific pathologies associated with difficult intubation:

  • Recent intubation (oedema, trauma, etc)
  • Angioedema
  • Airway trauma
  • Airway infection
  • Mediastinal mass, eg. retrosternal goitre
  • Ankylosing spondylitis
  • Acromegaly
  • Degenerative arthritis (i.e. of the C-spine or jaw)
  • Subglottic stenosis
  • Lingual hypertrophy (i.e. big fat tongue)
  • Syndromic appearance:
    •  Treacher-Collins syndrome: Auricular and ocular defects, malar and mandibular hypoplasia
    •  Pierre Robin syndrome: micrognathia, macroglossia,  cleft soft palate
    •  Down syndrome: small mouth; macroglossia
    • Goldenar’s syndrome: malar and mandibular hypoplasia
    • Kippel-Feil syndrome: congenital C-spine fusion

Physical examination: general features

  • Level of consciousness (i.e. is the patient cooperative enough for an awake intubation?)
  • Level of comfort (i.e. can the patient be positioned properly, or are they to short of breath?)
  • Pregnancy (makes everything difficult)
  • Syndromic appearance

Mouth, face and jaw examination

  • Long upper incisors (“buck teeth”)
  • No teeth (edentulous patients are easier to intubated, but harder to bag-mask ventilate)
  • Prominent overbite
  • Inability to “prognath”, i.e to voluntarily protrude the mandible
  • Small mouth opening (3cm is the minimum to comfortably admit a laryngoscope blade).
  • Mallampati score more than 2 (i.e. a barely visible uvula)
  • Arched or narrow palate
  • Compliance of the mandible and mandibular space (i.e. is it possible to manipulate it, or is it relatively fixed by some sort of disease process, eg. a submandibular abscess)
  • Beard
  • Patency of nares: polyps, deviated septum etc.

Neck and posture

  • Thyromental distance (“three ordinary finger breadths”, or 6cm)
  • Mandibulo-hyoid distance of less than 4cm
  • Sternomental distance of less than 12cm
  • Thick short neck
  • Restricted range of neck motion
  • Kyphosis

LEMON is a nice short way of remembering what to look for. It certainly seems to be reliable in predicting difficult intubation. 


  • Does the patient look like the stereotypical difficult intubation?

Evaluate: 3:3:2 rule

  • 3 fingers width of mouth opening
  • 3 fingers width of thyromental distance (from the thyroid cartilage to the mental process of the mandible, colloquially referred to as the chin)
  • 2 fingers width of distance from the hyoid to the thyroid

Mallamati score

  • amount of pharynx which can be seen by opening the mouth

Obesity and obstruction

  • Is the patient morbidly obese?
  • is there some sort of obstruction, eg abscess?

Neck mobility

  • this determines how easy it will be to align the planes


Arne, J., et al. "Preoperative assessment for difficult intubation in general and ENT surgery: predictive value of a clinical multivariate risk index." British journal of anaesthesia 80.2 (1998): 140-146.

Wilson, M. E., et al. "Predicting difficult intubation." British Journal of Anaesthesia 61.2 (1988): 211-216.

Cattano, D., et al. "Anticipation of the difficult airway: preoperative airway assessment, an educational and quality improvement tool." British journal of anaesthesia 111.2 (2013): 276-285.

Reed, M. J., M. J. G. Dunn, and D. W. McKeown. "Can an airway assessment score predict difficulty at intubation in the emergency department?." Emergency medicine journal 22.2 (2005): 99-102.

Apfelbaum, Jeffrey L., et al. "Practice Guidelines for Management of the Difficult AirwayAn Updated Report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway." The Journal of the American Society of Anesthesiologists 118.2 (2013): 251-270.

Nørskov, Anders Kehlet, et al. "Diagnostic accuracy of anaesthesiologists’ prediction of difficult airway management in daily clinical practice: a cohort study of 188 064 patients registered in the Danish Anaesthesia Database." Anaesthesia 70.3 (2015): 272-281.

Williamson, Dominic, and Jerry Nolan. "Airway assessment." Emergency Airway Management (2015): 41.

Huitink, J. M., and R. A. Bouwman. "The myth of the difficult airway: airway management revisited." Anaesthesia 70.3 (2015): 244-249.

Gupta, Sunanda, Rajesh Sharma, and Dimpel Jain. "Airway assessment: predictors of difficult airway." Indian J Anaesth 49.4 (2005): 257-262.