Coma is defined as a state in which the patient appears to be asleep, shows no awareness of his or her surroundings, and cannot be aroused. Coma frequently is only a transient state, whereby patients recover, die, or progress to a permanent state of impairment. Often a medical emergency, immediate intervention may be required to preserve life and brain function.

  • Coma is at the far end of a spectrum of acute impaired consciousness, which also includes the following:
    • Lethargy or stupor: patient arousable but does not stay awake; impaired responses to commands
    • Delirium: a confused, agitated or hypoactive patient with fragmented attention, concentration, and memory
  • Coma may progress to
    • Persistent vegetative state: chronic state of unconsciousness with no awareness or cognition, no voluntary responses, and no language abilities; preserved autonomic functions and sleep–wake cycles
    • Brain death: lack of cortical and brainstem responses


Incidence varies by age, season (infection), and ethnicity (inborn errors of metabolism [IEM]).


Dysfunction of the reticular activating system in the brainstem or bilateral cerebral dysfunction causes impaired arousal and consciousness.


Coma etiology can be traumatic or nontraumatic. Infection is a common cause of nontraumatic coma.

There's more to see -- the rest of this topic is available only to subscribers.