Functional: impairment of consciousness or neurological disease in a patient with an essentially normal airway. Patients with existing obstructive sleep apnoea are at particularly high risk. This is commonly encountered by acute physicians. Simple interventions may be sufficient whilst the underlying problem is identified and treated.

Mechanical: physical obstruction of the airway by a foreign body, tumour or oedema, for example. Anaesthetic or ENT expertise is often required, though temporizing measures are important whilst help is awaited.

Due to a combination of functional and mechanical factors: any functional cause of airway compromise may be complicated by mechanical obstruction, for example aspiration of vomitus in a patient intoxicated with alcohol. Likewise, uncorrected mechanical obstruction eventually results in exhaustion, asphyxia and loss of consciousness.

Obstruction tends to occur at sites of anatomical narrowing and the causes and clinical features differ according the level, though no sign or symptom is pathognomonic. The time course and degree of obstruction are also important. Common mechanical causes of airway obstruction are given in Table 59.1.