Coma is a profound state of unconsciousness.A person in a coma cannot be awakened, fails to respond normally to pain, lightor sound, does not have sleep-wake cycles, and does not take voluntaryactions. A person in a state of coma can be described as comatose.
Coma may result from a variety of conditions, including intoxication,metabolicabnormalities, central nervous system diseases, acute neurological injuriessuch as stroke,and hypoxia. A coma may also result from head traumacaused by mechanisms such as falls or caraccidents. It may also be deliberately inducedby pharmaceutical agents in order to preserve higher brain function followinganother form of brain trauma, or to save the patient from extreme pain duringhealing of injuries or diseases. The underlying cause of coma is bilateraldamage to the Reticular formation of the hindbrain,which is important in regulating sleep.
If the cause of coma is not clear, various investigations (blood tests,medicalimaging) may be performed to establish the cause and identify reversiblecauses. Coma usually necessitates admission to a hospital andoften the intensive care unit.
The severity and mode of onset of coma depends on the underlying cause. Forinstance, deepening hypoglycemia (low blood sugar) or hypercapnia(increased carbon dioxide levels in the blood) initially causemild agitation and confusion, then progress to obtundation,stupor and finally complete unconsciousness. In contrast, coma resulting from asevere traumatic brain injury or subarachnoid hemorrhage can beinstantaneous. The mode of onset may therefore be indicative of the underlyingcause.
In the initial assessment of coma, it is common to gauge the level of consciousness by spontaneouslyexhibited actions, response to vocal stimuli ("Can you hear me?"),and painful stimuli; this is known as the AVPU (alert, vocal stimuli, painfulstimuli, unconscious) scale. More elaborate scales, such as the Glasgow coma scale quantify individual reactionssuch as eye opening, movement and verbal response on a scale.
In those with deep unconsciousness, there is a risk of asphyxiationas the control over the muscles in the face and throat is diminished. As aresult, those presenting to a hospital with coma are typically assessed forthis risk ("airway management"). If the risk ofasphyxiation is deemed to be high, doctors may use various devices (such as an oropharyngeal airway, nasopharyngeal airway or endotrachealtube) to safeguard the airway.
Once a person in a coma is stable, investigations are performed to assessthe underlying cause. These may be simple; a computed tomography scan of the brain, forexample, is performed to identify specific causes of the coma, such as hemorrhage.
A diagnosis will direct the appropriate therapy; however it does not reducethe need for generic supportive care, such as that offered on intensive care.Sometimes, the diagnosis allows the withdrawal of care, if the cause of coma isuntreatable and the brain damage is irreversible.