A coma is commonly referred to as a persistent vegetative state and is defined as a deep or profound state of unconsciousness. Someone in a coma is not brain-dead - he/she is alive but not able to move or react to his/her surroundings. State of coma may occur as a result of pre-existing illness or condition, and may also be caused by head injuries. A person in persistent vegetative state has lost his/her ability to think and is not aware of his/her surroundings. Despite this, the person retains non-cognitive brain function and normal sleep patterns.

The main causes of a coma is bleeding or swelling that affects the brain, insufficient oxygen or blood sugar and assorted poisons that injure the brain.

The most important aspect of treating a coma patient is the prevention of secondary brain injury. Intracranial pressure and swelling can occur after head trauma and surgery may be needed to relieve pressure on the brain. This type of surgery is called a craniotomy and consists of creating holes in the skull to allow excess blood and fluid to drain. Antibiotics can be given to patients to treat infections. Glucose or insulin and anti-seizure medications are also prescribed to coma patients in some cases.

The outlook for coma patients can vary greatly and depends largely on the severity of the initial injury, as well as the amount of time spent in a comatose state. It is possible for some to regain their motor and cognitive skills through extensive rehabilitation.