Assessing Difficult Airways

The maintenance of a patient's airway can be made more difficult by a variety of factors. The most important is the anatomy of the oropharynx and neck. Luckily there is a creative acronym to remember these factors, LEMON. 

The LEMON Acronym

The LEMON acronym stands for Look, Evaluate, Mallampati, Obstruction, and Neck.

Look – Look externally. There may be some physical clue or foreign object that would indicate obvious difficulty.

Evaluate – Evaluate using the 3-3-2 rule. If the airway is larger or smaller than these measurements, it may indicate a difficult airway.

1.  Can the patient fit 3 fingers between their incisors?
2.  Is the mandible 3 fingers long from the chin to the hyoid?
3.  Is the distance from the hyoid to the thyroid 2 fingers wide?

Mallampati – This is a simple scoring system that compares how much the mouth can open and the size of the tongue; it indicates an estimate of space available for oral intubation by direct laryngoscopy. The Mallampati classification ranges from I – IV (easiest → most difficult) depending on what you see when opening the patient's mouth.

1. Class I: you can see the lateral tonsillar pillars, uvula, and soft palate.
2. Class II: the top of the uvula is still visible, but the bottom is occluded by the arching horizontal posterior tongue. The soft palate is still visible.
3. Class III: only the soft palate is visible.
4. Class IV: only the hard palate is visible. The horizontal arching of the tongue is in front of all else (uvula, soft palate, tonsillar pillars).

Obstruction – Look for anything that might get in your way, like soft-tissue swelling, burns, fractured necks, trauma to the face or neck, foreign bodies, and excessive soft tissue from obesity. The redundant tissues in the upper airway of obese patients make visualization of the glottis by direct laryngoscopy difficult, so a larger (oversized) laryngoscope blade may be necessary.

Neck – Neck mobility is desirable. Unfortunately, many patients who need resuscitation need, or are already wearing, C-collars, and you may not be able to manipulate the neck. Without spinal precautions, the sniffing position is best for visibility.