Altered mental status is a change in baseline level of awareness, cognition, attention, or consciousness.
Behavior ranges from subjective difficulty thinking clearly to abnormal thought content, states of depressed consciousness, and agitation.
Adjunctive complaints such as dyspnea, hypoxia, high fever, or acute focal neurologic deficits help prioritize the differential diagnosis.
Requirement for consciousness
Intact and functioning brainstem reticular activating system and its cortical projections.
Terminology for impaired levels of consciousness, in order of increasing severity
Confusion: Impairment of the capacity to think with normal speed and clarity, associated with inattentiveness and disorientation. Delirium is a special example of an acute confusional state in which impaired attention and reasoning are associated with agitation, hallucinations, and in some cases, tremor and convulsions.
Drowsiness: Inability to remain awake without external stimulation; often associated with some degree of confusion.
Stupor: State in which only vigorous external stimulation can arouse the patient; once aroused, responses remain markedly impaired.
Coma: Deep sleep-like state; patient cannot be aroused even with vigorous or repeated external stimulation.