A difficult airway may present as difficult ventilation, difficult laryngoscopy, difficult intubation or a combination of these. 30 - 40% of anaesthetic related deaths are due to the inability to manage the airway, resulting in hypoxia. The definition of difficult intubation is greater than 3 attempts at intubation, or greater than 10 minutes of attempted intubation. The incidence of difficult intubation is about 0.5 - 16.6% (the rate varies depending on the definition). 15% of difficult intubations were also associated with difficult mask ventilation.
Successful airway management ensure adequate tissue oxygenation. Most airway related deaths and morbidity result from a failure to ventilate and oxygenate rather than a failure to intubate. It is important for the anaesthetist to be skilled at airway management without tracheal intubation.
Anaesthetic facemasks are designed to fit the contours of the face with minimal pressure. They are cushioned to minimize the leakage of gases and come in different sizes. The correct size for the patient will minimize dead space and provide a good seal. Paediatric masks can be cushioned circular masks or the Rendell-Baker mask, which is designed to minimize dead space.
Once the patient loses consciousness in the supine position, the tongue and epiglottis fall towards the posterior pharyngeal wall tending to obstruct the upper airway. The anaesthetist can perform chin lift and jaw thrust manoeuvres to open the airway. The facemask is held onto the face using the thumb at the bridge of the nose, fifth finger behind the angle of the mandible and the rest of the fingers pull the mandible into the mask. The mask should not be pushed onto the face. Edentulous patients and beards will make it difficult to achieve an adequate seal with a facemask for positive pressure ventilation.
Pharyngeal airways relieve upper airway obstruction caused by soft tissue relaxation during unconsciousness. They are able to separate the soft tissues from the posterior pharyngeal wall. Insertion will require attenuation of the upper airway reflexes to prevent regurgitation, gagging and laryngospasm. Measuring the distance from the tragus of the ear to the corner of the mouth allow the anaesthetist to choose the correct size of an oral airway.
Laryngeal mask airway
The LMA consists of an elliptical bowl-shaped mask that sits over the laryngeal inlet surrounded by a cuffed rim. There is a tubular portion that sits in the oropharynx and mouth. It can be connected to the breathing circuit. It is available in adult and paediatric sizes and there is now a version with a gastric lumen that sits in the upper oesophagus to reduce the risk of regurgitation into the larynx (ProSeal). A reinforced version is also available.