Coma may be defined as an abnormal state of profound unconsciousness, lasting for an indefinite, possibly prolonged, period. It is usually subsequent to head trauma, stroke, severe injury, substance intoxication, tumor, or underlying illness. A comatose individual exhibits no voluntary movement or behavior, reflexes may be absent, and, in deep coma states, there may be a lack of response to ordinarily painful stimuli.
A coma may occur by a variety of means and may be temporary or permanent. There are times when it is in a patient's best interest for future recovery to place the individual in a deeply sedated state, called a medication-induced coma, for a specific period of time. A comatose individual cannot be aroused by even the most intense stimuli, although the person may, depending on the depth of the coma, show some automatic movements in response to pain. Coma occurs shortly before death in the course of many diseases, as the body moves through the process of shutting down. The affected brain cells may be near the surface, in the cerebral cortex, or deeper in the brain, in the diencephalon or brainstem. Some specific conditions that may produce coma are cerebral hemorrhage; blood clots in the brain; loss of oxygen supply to the brain; tumors; intracranial infections causing meningitis or encephalitis; toxicity or poisoning, especially by carbon monoxide or sedatives; concussion or traumatic brain injury; and disorders involving electrolytes. Comas may also be caused by metabolic abnormalities that impair the brain's functioning, due to a sharp drop in the blood sugar level, as may sometimes happen with diabetes.
The Glasgow Coma Scale is one standard used to assess depth and severity of coma, by measuring motor response from no response to obeying commands fully; verbal response from no response to alert and oriented; and eye opening from no eye opening to spontaneous eye opening. Coma severity is ranked in the following order: mild, moderate disability, severe disability, vegetative state, persistent vegetative state, brain death.
The passage from wakefulness to coma may be rapid or gradual. It is sometimes preceded by lethargy and then a state resembling light sleep. In general, treatment of a coma involves supporting the integrity of the organism and maintaining homeostasis, avoiding further damage to the brain by keeping the patient's respiratory, cardiac and circulatory systems stable, and by supplying necessary nutrients either intravenously or through the use of a gastric tube.
See also Brain injuries ; Cognition ; Consciousness .
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