Assessment and management of the patient with impaired consciousness

Coma and impaired consciousness are frequent medical emergencies. Assessment of such patients requires a working knowledge of the neuro-anatomical basis of consciousness. Consciousness is dependent upon the integrity of two structures: the reticular activating system in the brainstem, which governs the level of arousal, and the cerebral cortex of both hemispheres, which determines the content of consciousness. Coma can result either from pathological processes in the brainstem or from diffuse pathology in the cerebral cortex. The Glasgow Coma Score (GCS) is invaluable for documenting the level of coma and monitoring for clinical change, but is of no diagnostic significance. A thorough neurological assessment should allow separation of patients into three separate groups: high likelihood of structural supra- or infratentorial pathology requiring urgent CT brain scans (e.g. cerebrovascular disease); coma with meningeal irritation where lumbar puncture and prompt antibiotic therapy may be life-saving (e.g. bacterial meningitis); and patients with no focal signs or meningeal irritation where metabolic and toxic causes are common (e.g. drug overdose, hypoglycaemia, hyponatraemia and liver failure). The prognosis of coma depends on aetiology, depth and duration of coma and presence of brainstem reflexes.