Airway Evaluation (details)
EXAMINATION & CLINICAL TESTS
This is not an exhaustive list of tests. Others not mentioned here have been described and used.
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Like any diagnostic test, an ideal method of preoperative airway assessment should have high sensitivity and specificity. No single test or score for airway assessment meets these requirements.
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Patient features
There are a number of anatomical features of the patients face and neck which predict difficult laryngoscopy, such as a small mouth (related to but not the same as 'poor mouth opening/ small interincisor gap'), an arched/ high palate, a short neck, or protruding/ 'buck' teeth. All these features are somewhat difficult to quantify.
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Mallampati score
As described in Mallampati's original paper from 1985, this is assessed by asking the patient (in a siting or upright position) to open his/ her mouth and protrude the tongue maximally. Visibility of faucial pillars, soft palate and uvula inside the patient's mouth will result in a score of one to three. A Mallampati score of four was later added.
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Mallampati 1
Faucial pillars, soft palate and entire uvula can be visualized.
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Mallampati 2
Faucial pillars and soft palate can be visualized. The uvula is masked by the base of the tongue.
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Mallampati 3
Only the soft palate is visible.
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Mallampati 4
The soft palate is not visible, i.e. only the hard palate can be visualized at the roof of the mouth.
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Mallampati in his original paper demonstrated the relationship between his scoring system and ease of laryngoscopy. Most patients with a score of one would have a grade 1 Cormack-Lehane view during laryngoscopy, most patients with a score of two would have a grade 2 view and most patients with a score of three would have a grade 3 view.
Mouth opening/ interincisor gap
Reduced mouth opening is associated with difficult laryngoscopy and intubation. But how do we differentiate between 'good' and 'poor' mouth opening without a tape measure? One helpful way to quantify mouth opening is to ask the patient whether he/ she can place three fingers between their upper and lower teeth (see picture below). Whereas three finger-breadths is ideal, anything less than two (around 3 cm) predicts an increased risk of difficult laryngoscopy.
Thyromental distance
This should ideally be greater than 6.5 cm, which is about three finger-breadths.
Mandibular protrusion
Asking patients to 'protrude their mandible' might just draw a blank. It might be easier to ask "can you bite your top lip?" or "can you show me your teeth and push your chin forward?".
Mandibular protrusion has been classified into three grades.
