Coma and Persistent Vegetative State


What Is It?

Coma is a deep and prolonged state of unconsciousness resulting from disease, injury or poisoning. The word coma usually refers to the state in which a person appears to be asleep, but cannot be awakened. There also is another type of coma, called persistent vegetative state or awake coma, in which the person appears to be awake, but does not respond to the outside world. In this type of coma, the person’s eyes may be open and there may be some yawning, grunting or other vocalizations. In both cases, the patient is alive, but the brain does not function fully.

Some causes of coma include:

  • Head trauma, such as may be sustained in a car accident, sports injury or falling injury

  • Complication of an underlying disease, such as seizure disorder, diabetes or liver or kidney failure

  • Poisoning, usually involving an overdose of drugs that depress the nervous system, such as tranquilizers or alcohol

  • Stroke


A person in a coma will be unconscious and unable to communicate, but still breathing and alive. The person cannot be aroused from this state.


Coma is usually a straightforward diagnosis because the signs of unconsciousness and unresponsiveness are clear. The cause of the coma can be more difficult to determine.

When coma results from traumatic Head injury, the cause usually is clear from the injuries. Other clues to the cause of coma may be available from the people who called for help. For example, observers can tell health care providers whether the person took a large quantity of medication, what symptoms occurred immediately before the coma, and how quickly the person lost consciousness. Doctors also will want to know about the patient’s medical history, because some disorders can lead to coma, including diabetes, seizure disorder and a history of heart, lung, liver, kidney or other disease. A physical examination can give other clues. For example, very small (pinpoint) pupils that do not react to bright light are seen in narcotic overdose.

Specific tests that may be used to diagnose coma include:

  • Blood and urine tests to check for disease, metabolic disorders or toxins

  • magnetic resonance imaging or Computed tomography scans to look for bleeding in the brain, tumors, infection or stroke from decreased blood flow

  • Electroencephalogram , a graph of the electrical output of the brain that may indicate a metabolic imbalance or persistent seizure activity

  • Lumbar puncture (spinal tap) to examine the cerebrospinal fluid for signs of meningitis and encephalitis

Expected Duration

How long a coma lasts depends on the cause, location, extent and severity of the damage to the brain. Coma can last hours or years, and can end with recovery or death. Some people who recover from a coma will have permanent physical or psychological disabilities. Some face years of rehabilitation, and others recover fully relatively quickly.


Although coma sometimes cannot be prevented, most cases of coma can be prevented by using safety precautions. For example, many cases of head trauma could be prevented if more people drove safely, wore seat belts when riding in an automobile, and wore helmets when riding on a motorcycle or bicycle. Also, do not drive when drinking alcohol or taking sedating drugs. People with diabetes need to monitor their blood sugar levels often to avoid hypoglycemia. Many medications interact to decrease levels of consciousness, especially when mixed with any alcohol.


Treatment starts with reducing further damage to the brain. Physicians will assure that the patient’s airways are clear and that he or she is able to breathe. In some cases, the person will have to be put on a ventilator (a mechanical breathing machine).

Specific treatment will depend on the cause of the coma. For example, if the coma was caused by head trauma, efforts will be made to stop any bleeding or swelling in the brain. If the coma was caused by a metabolic imbalance, physicians will try to reverse it by treating the underlying condition. If poisoning caused the coma, physicians may give medications to counteract the depressive effects of the substance that caused the coma.

Once the person is treated appropriately for the immediate cause of coma, treatment will focus on supportive care. This usually includes making sure the person does not suffocate, making sure the person’s muscles and ligaments stay flexible, providing adequate nutrition, and preventing infections, such as pneumonia. Because a person in a coma cannot move on his or her own, it’s important that his or her body be rotated periodically to prevent bedsores.

When To Call A Professional

Seek emergency care if a person appears to be unconscious, is unable to respond, or cannot be awakened from a sleep.


Some people make a full recovery, others recover with some remaining physical or intellectual effects, and others die of their injuries or condition. It is not always possible to predict who will recover and who will not. Recovery is more likely from a coma resulting from a metabolic disorder, such as diabetes, than from a coma caused by trauma. People in a persistent vegetative state rarely recover. In general, the longer the coma, the less likely the person is to recover.

People who awaken from a coma often do so slowly, over days. Although comas rarely last longer than four weeks, some people can remain in a coma or persistent vegetative state for months or years.

Johns Hopkins patient information

Last revised:

Diseases and Conditions Center

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.