The airway

Published on 06/02/2015 by admin

Filed under Anesthesiology

Last modified 06/02/2015

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TOPIC 1 The airway

Topic Contents

Predicting difficult airway management 1

Test: Bedside tests 1
View at laryngoscopy 4

Test: Cormack and Lehane view 4
Other investigations of the airway 5

Test: Soft tissue imaging of the lower airway 5
Test: Flexible nasendoscopy 5
Test: Flow volume loops 5
Test: Plain radiography 6

Predicting difficult airway management

Test: Bedside tests

Indications

Used to predict difficult facemask ventilation and tracheal intubation. They should form part of the routine clinical examination of the patient during the anaesthetist’s preoperative assessment, and should be performed in conjunction with a full history and physical examination as appropriate. The latter will not be discussed further in this topic.

Failed intubation and ventilation leading to serious morbidity or death is generally accepted as having an incidence of 1 in 10 000 to 1 in 100 000 of the general surgical population.

The most commonly used tests are listed below.

Mallampati test

First described in 1984 as a three-point scoring system. A modification by Samsoon and Young into a four-point system has generally been accepted.

How it is done

Keeping the head in a neutral position the patient is asked to open the mouth fully and protrude the tongue as far as possible, without phonation. Looking from the patient’s eye level the pharyngeal structures are inspected (Fig. 1.1). It has been suggested that the specificity and positive predictive value of the modified Mallampati test is improved by slightly extending the neck.

image

Fig. 1.1 Modified Mallampati classification.

Interpretation

The following structures are visible:

Class I – soft palate, fauces, uvula, anterior and posterior pillars
Class 2 – soft palate, fauces and uvula
Class 3 – soft palate and the base of the uvula
Class 4 – soft palate is not visible at all.

Management principles

A prediction of a difficult airway may trigger an alternative management strategy, for example inhalational induction, fibre-optic intubation or awake percutaneous approach under local anaesthesia.

Limitations and complications

• There is no universally accepted definition of what constitutes difficult airway management, which is itself subject to the expertise of the anaesthetist. It can be defined according to time taken, attempts made, hypoxaemia or requirement for a second dose of muscle relaxant.
• Because true failed airway management is very rare (1 in 3000 of the general surgical population), none of the commonly used bedside tests are reliably able to identify those at risk of difficult airway management without a high false negative rate.
• Used alone, therefore, the Mallampati test has limited accuracy for predicting the difficult airway and its use as a screening tool has been called into question. It is undoubtedly valuable when used in conjunction with other bedside tests.

Protrusion of the mandible

This gives an indication of the mobility of the mandible. This can be graded as follows:

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