Coma

A coma is a prolonged state of deep unconsciousness in which a person cannot be awakened and fails to respond normally to stimuli such as pain, light, or sound, with no conscious feeling, speech, voluntary movement, or normal sleep-wake cycle. It results from injury to either the cerebral cortex or the reticular activating system in the brainstem, the two structures the brain needs to sustain consciousness, and it has many possible causes: drug poisoning accounts for an estimated forty percent of cases, oxygen deprivation such as from cardiac arrest for about twenty-five percent, and stroke, brain hemorrhage, or brain tumors for roughly twenty percent, with traumatic brain injury, blood loss, malnutrition, hypothermia, abnormal blood sugar, seizures, kidney or liver failure, and brain infection among the other recognized causes. Comas can last from several days to, in extreme cases, years, and the chance of even partial recovery falls below fifteen percent after four months of coma caused by brain damage, with full recovery unlikely beyond that point.