Coma

Coma is a pathological state of unconsciousness from which a patient cannot be roused to wakefulness by stimuli, and reflects dysfunction of the brainstem reticular system and its thalamic projections (the neuronal basis of wakefulness), or diffuse injury of both cerebral hemispheres. A unilateral lesion of a cerebral hemisphere (e.g. haemorrhagic stroke) will not cause coma unless there is secondary compression of the contralateral hemisphere or brainstem. Coma is a medical emergency, because a comatose patient is at high risk of permanent brain injury or death, caused either by the underlying disorder or the secondary effects of coma. Stabilization of the airway, breathing, and circulation, and exclusion of hypoglycaemia are the first priorities, before diagnosis is explored further. Clinical assessment together with neuroimaging will usually identify the likely cause or causes. The clinical approach to diagnosis and management of the comatose patient is described in this chapter.