An abnormal state of profound unconsciousness accompanied by the absence of all voluntary behavior and most reflexes.
A coma may be induced by a severe neurological injury—either temporary or permanent—or by other physical trauma. A comatose individual cannot be aroused by even the most intense stimuli, although he or she may show some automatic movements in response to pain. Comas often occur just before death in the course of many diseases. The affected brain cells may be either near the surface (cerebral cortex) or deeper in the brain (diencephalon or brainstem). Specific conditions that produce comas include cerebral hemorrhage; blood clots in the brain; failure of oxygen supply to the brain; tumors; intracranial infections that cause meningitis or encephalitis; poisoning, especially by carbon monoxide or sedatives; concussion; and disorders involving electrolytes. Comas may also be caused by metabolic abnormalities that impair the functioning of the brain through a sharp drop in the blood sugar level, such as diabetes.
The passage from wakefulness to coma can be rapid and/or gradual. Often, it is preceded by lethargy and then a state resembling light sleep. In general, treatment of a coma involves avoiding further damage to the brain by maintaining the patient's respiratory and cardiac functions, and by an intravenous (usually glucose) nutritional supply to the brain.