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Why is airway management needed in anaesthesia?

Patients undergoing anaesthesia or sedation are at risk of both airway obstruction (from relaxation of musculature supporting the upper airway) and apnoea (caused by respiratory depression and/or paralysis). As oxygen storage in the functional residual capacity in the lungs, even with preoxygenation, is very limited (at most 5 minutes), restoring airway patency is a critical role.


What are supraglottic devices?

The distal end of these devices stops above the vocal cords. There are a number of devices that come under this heading, including simple oral airway (Guedel airway), nasopharyngeal tube, and a laryngeal mask airway (LMA).


What is a Guedel airway? How does it work? How should it be measured?

This device is inserted upside down over the tongue to prevent it moving backwards and obstructing the airway. It is available in various sizes. It can be measured either from the incisors to the angle of the mandible or from the chin to the tragus. The cuffed oropharyngeal airway is a modification of the Guedel. This has a distal cuff, which pushes the tongue forwards and creates an airtight seal. The proximal end can be connected to an aneesthetic unit.


What is a nasopharyngeal airway?

This is lubricated and inserted through the nares and horizontally into the nasopharynx. It is useful when you do not wish to, or are unable to use the patients mouth. It is tolerated at lighter levels of anaesthesia and also allows suction of the pharynx. Haemorrhage may occur during insertion which is a drawback.


What is an LMA?

There are many variants of this device available, but the principle is the same for each. When correctly placed it sits over the glottis, however, it does not protect against airway soiling like an ET tube does. Also, it will not allow ventilation with high airway pressure (high resistance/ low compliance).


What are infraglottic devices?

The tip of these devices is positioned below the level of the vocal cords. Unlike supraglottic devices, they need much more skill at positioning, usually with a laryngoscope but sometimes they are positioned "blind" or fibre optically. Again there are many variants of the ET tube and some are more suitable for specific surgical approaches. The gold standard is still the endotracheal tube.


What is meant by an emergency airway?

These devices are used in order to allow a patent airway when intubation is not possible and especially in the most serious airway of all - can't intubate, can't ventilate (CVCI). The final step in this pathway (following failed mask oxygenation, and LMA insertion) is surgical access to the airway. This involves the use of a cannula or direct surgical access via the cricothyroid membrane into the airway.


What features should form part of the airway assessment?

Traditionally, the gold standard of airway management is tracheal intubation, and the majority of assessments relate to the ease or difficulty of this process.

1) History - past anaesthetic history, surgery radiotherapy to head/neck, OSA, conditions affecting tongue size (e.g. acromegaly, infections), conditions affecting neck mobility (e.g. AS), conditions affecting mouth opening (e.g. TMJ dysfunction)

2) General examination:
- look for external signs of surgery/ radiotherapy
- assess the airway from the from the front of the patient, including: receding jaw, protruding upper incisors, large tongue, large neck, obesity
- tumours, infection, trauma, swelling or burns and scarring of the tongue strongly suggest airway problems

3) Tests:
- mouth opening - 4-6cm
- Mallampati classification (scores of 3 and 4 are associated with a difficult airway)
- forward movement of the jaw - i.e. ability to protrude lower teeth in front of upper teetj
- thyromental distance (chin to thyroid notch): this should be >6cm
- atlanto-occipital mobility
- radiology/ imaging


What options are available for airway management in a patient with a known or suspected difficult airway?

1) Do you need to give a GA - what about a regional technique?
2) Do you need tracheal intubation - what about LMA?
3) If you do need intubation, is it safe/ appropriate to have a look?

Other adjuncts may be required to tracheal intubation, including:
- fibre optic intubation - larynx is visualised and then a tube railroaded over the top of the "scope". Can be performed with the patient awake or asleep. Airway needs prior preparation (local anaesthesia and vasoconstriction)
- intubating LMA - tracheal tube is inserted down the inside of an LMA
- other equipment such as bougies


What pathologies may make the neck unstable for airway management?

Downs syndrome