the airway


All patients must have an assessment made of their airway, the aim being to try and predict those patients who may be difficult to intubate.


Observation of the patient’s anatomy

Look for:

  • limitation of mouth opening;
  • a receding mandible;
  • position, number and health of teeth;
  • size of the tongue;
  • soft tissue swelling at the front of the neck;
  • deviation of the larynx or trachea;
  • limitations in flexion and extension of the cervical spine.

Finding any of these suggests that intubation may be more difficult. However, it must be remembered that all of these are subjective.


Simple bedside tests

  • Mallampati criteria The patient, sitting upright, is asked to open their mouth and maximally protrude their tongue. The view of the pharyngeal structures is noted and graded I–IV. Grades III and IV suggest difficult intubation.
  • Thyromental distance With the head fully extended on the neck, the distance between the bony point of the chin and the prominence of the thyroid cartilage is measured. A distance of less than 7 cm suggests difficult intubation.
  • Wilson score Increasing weight, a reduction in head and neck movement, reduced mouth opening, and the presence of a receding mandible or buck-teeth all predispose to increased difficulty with intubation.
  • Calder test The patient is asked to protrude the mandible as far as possible. The lower incisors will lie either anterior to, aligned with or posterior to the upper incisors. The latter two suggest reduced view at laryngoscopy.

None of these tests, alone or in combination, predicts all difficult intubations. A Mallampati grade III or IV with a thyromental distance of <7cm predicts 80% of difficult intubations. If problems are anticipated, anaesthesia should be planned accordingly.


If intubation proves to be difficult, it must be recorded in a prominent place in the patient’s notes and the patient informed.