5. AIRWAY ASSESSMENT

One in a hundred tracheal intubations may be difficult. By taking a history and performing an examination, the anaesthetist may identify those patients that may be difficult to intubate.

Preoperative Assessment

Intubation may be difficult because the patient has reduced mouth opening (e.g. osteoarthitis, trauma, rheumatoid arthitis, infection), reduced neck flexion/extension (e.g. osteoarthitis, trauma, rheumatoid arthitis, ankylosing spondylitis), lesions in the oral cavity (e.g. swelling, infections or tumours of larynx, pharynx, tongue) or congenital facial abnormalities. Intubation may also be difficult in patients who are obese or have large breasts.

Anaesthetic History

The anaesthetist’s preoperative history should determine if the patient has had problems with an anaesthetic in the past. The anaesthetist must look at the patient’s old anaesthetic notes to see if there have been problems with intubation during previous anaesthetics. (If the anaesthetist has a problem with intubation or any part of the anaesthetic they must write a clear account of that problem to warn other anaesthetists). The anaesthetist should also ask about a history of arthitis in the neck, infections or tumours in the mouth, trauma to the neck or mouth, loose teeth and dentures and also ask about any symptoms of airway obstruction such as hoarse voice, stridor, wheezing and airway obstruction with changes in the patient’s position.

Physical Examination

The physical examination is very important. The anaesthetist should assess the patient’s mouth opening, cervical spine mobility, teeth, thyromental distance, and mouth cavity.

The anaesthetist must perform a complete airway assessment for every patient.

The patient should be able to open their mouth more than thee fingers breadth.

They should be able to touch their chin to their chest and also extend their neck backwards.

Large front teeth will make intubation more difficult and bad teeth may be damaged or lost during intubation.

If the thyromental distance (the distance between the lower border of the mandible to the thyroid notch) is less than four fingerbreadths, there may be difficulty seeing the glottis.

Mallampati Classification

The mouth cavity should be assessed by sitting the patient upright with the head in a normal position, mouth open as wide as possible and tongue poking out. The airway can then be given a Mallampati score depending on how much of the oral cavity can be seen.

 (Class 1:soft palate, uvula, fauces and pillars; class2: soft palate, uvula, fauces; class3: only soft palate and class 4: soft palate not visible).

If the patient has a Mallampati class 1 airway and no other airway problems, most intubations will be easy.

If the patient has a Mallampati class 4 airway then intubation may be difficult.

Patients with more than one airway abnormality are more likely to have a difficult intubation. For example, an obese patient with a short neck, reduced movement in the cervical spine and reduced thyromental distance, or a patient with large upper teeth, small mouth and small mandible.

Laboratory Investigations

In most patients a good history and examination will warn the anaesthetist of a difficult airway, and investigations are not required.

Chest and cervical spine neck X-rays can reveal tracheal deviation or narrowing. Cervical spine X-rays are very important in trauma patients.

Indirect laryngoscopy can show lesions of the pharynx and larynx.

Arterial blood gases can show the severity of the patient’s respiratory disease.

Conclusions

Anticipation of a difficult airway will help the anaesthetist to best manage the airway and avoid disasters. If the anaesthetist anticipates a difficult airway they must plan how to manage the airway. They should also plan what they would do if the first plan is not successful.

If the anaesthetist does not assess the patient’s airway, they will not be prepared to manage the patient who is difficult to intubate. If the patient’s airway is managed badly the patient may suffer severe complications or death.

A difficult airway cannot always be predicted. The anaesthetist must always be prepared to manage an unexpected difficult airway.