No single airway test can provide a high index of sensitivity and specificity for prediction of difficult airway.

 

Therefore it has to be a combination of multiple tests.

 

It must be recognized, however, that some patients with a difficult airway will remain undetected despite the most careful preoperative airway evaluation.

 

Thus, anaesthesiologists must always be prepared with a variety of preformulated and practiced plans for airway management in the event of an unanticipated difficult airway.

 

Studies from the anesthesiology literature suggest that 1 in 10,000 patients has an unpredicted difficult airway and data from emergency departments indicate that 1% of patients will have a failed airway; that is, the patient cannot be intubated within three attempts by a skilled operator.

 

The mnemonic "LEMON" can be an invaluable tool used to evaluate patient's for a potentially difficult airway.

L = Look.  For every patient who may require intubation, the physician should always look for readily apparent, even cosmetic, characteristics that may predict a potentially difficult airway.

 

E = Evaluate the 3-3-2 rule.  The 3-3-2 rule holds that in patients with normal relative anatomy the following apply: normal mouth opening is three fingerbreadths; a normal mandible dimension will likewise allow three fingerbreadths between the mentum and the hyoid bone; and the notch of the thyroid cartilage should be two fingerbreadths below the hyoid bone.

 

M = Mallampati score.  The Mallampati rule states that there is a relationship between what is seen on direct peroral pharyngeal visualization and that seen with laryngoscopy.  The exam can be approximated in supine and comatose patients using a tongue blade.

 

O = Obstruction.  Evaluation for stridor, foreign bodies, and other forms of sub/supraglottic obstruction should be performed in every patient prior to laryngoscopy.

 

N = Neck mobility.  Patients with degenerative or rheumatoid arthritis may have limited neck motion, and this SHOULD be assessed to assure the ability to adequately extend the neck during laryngoscopy.  Patients in whom traumatic c-spine injury is suspected, and in whom the c-spine has been immobilized by a cervical collar have limited neck mobility by definition. However this factor in isolation is typically not a significant hindrance to peroral direct laryngoscopy and intubation.