Coma: Types, Causes, Treatments, Prognosis

Medically Reviewed by Christopher Melinosky, MD on September 11, 2022
5 min read

A coma is a prolonged state of unconsciousness. During a coma, a person is unresponsive to their environment. The person is alive and looks like they are sleeping. However, unlike in a deep sleep, the person cannot be awakened by any stimulation, including pain.

Comas are caused by an injury to the brain. Brain injury can be due to increased pressure, bleeding, loss of oxygen, or buildup of toxins. The injury can be temporary and reversible. It also can be permanent.

More than 50% of comas are related to head trauma or disturbances in the brain's circulatory system. Problems that can lead to coma include:

  • Anoxic brain injury. This is a brain condition caused by total lack of oxygen to the brain. Lack of oxygen for a few minutes causes cell death to brain tissues. Anoxic brain injury may result from heart attack (cardiac arrest), head injury or trauma, drowning, drug overdose, or poisoning.
  • Trauma: Head injuries can cause the brain to swell and/or bleed. When the brain swells as a result of trauma, the fluid pushes up against the skull. The swelling may eventually cause the brain to push down on the brain stem, which can damage the RAS (Reticular Activating System) -- a part of the brain that's responsible for arousal and awareness.
  • Swelling: Swelling of brain tissue can occur even without distress. Sometimes a lack of oxygen, electrolyte imbalance, or hormones can cause swelling.
  • Bleeding: Bleeding in the layers of the brain may cause coma due to swelling and compression on the injured side of the brain. This compression causes the brain to shift, causing damage to the brainstem and the RAS (mentioned above). High blood pressure, ruptured cerebral aneurysms, and tumors are non-traumatic causes of bleeding in the brain.
  • Stroke: When there is no blood flow to a major part of the brain or loss of blood accompanied with swelling, coma can occur.
  • Blood sugar: In people with diabetes, coma can occur when blood sugar levels stay very high. That's a condition known as hyperglycemia. Hypoglycemia, or blood sugar that's too low, can also lead to a coma. This type of coma is usually reversible once the blood sugar is corrected. However, prolonged hypoglycemia can lead to permanent brain damage and persistent coma.
  • Oxygen deprivation: Oxygen is essential for brain function. Cardiac arrest causes a sudden cutoff of blood flow and oxygen to the brain, called hypoxia or anoxia. After cardiopulmonary resuscitation (CPR), survivors of cardiac arrest are often in comas. Oxygen deprivation can also occur with drowning or choking.
  • Infection: Infections of the central nervous system, such as meningitis or encephalitis, can also cause coma.
  • Toxins: Substances that are normally found in the body can accumulate to toxic levels if the body fails to dispose of them correctly. As an example, ammonia due to liver disease, carbon dioxide from a severe asthma attack, or urea from kidney failure can accumulate to toxic levels in the body. Drugs and alcohol in large quantities can also disrupt neuron functioning in the brain.
  • Seizures: A single seizure rarely produces coma. But continuous seizures -- called status epilepticus -- can. Repeated seizures can prevent the brain from recovering in between seizures. This will cause prolonged unconsciousness and coma.

Types of coma can include:

  • Toxic-metabolic encephalopathy. This is an acute condition of brain dysfunction with symptoms of confusion and/or delirium. The condition is usually reversible. The causes of toxic-metabolic encephalopathy are varied. They include systemic illness, infection, organ failure, and other conditions.
  • Persistent vegetative state. This is a state of severe unconsciousness. The person is unaware of their surroundings and incapable of voluntary movement. With a persistent vegetative state, someone may progress to wakefulness but with no higher brain function. With persistent vegetative state, there is breathing, circulation, and sleep-wake cycles.
  • Medically induced: This type of temporary coma, or deep state of unconsciousness, is used to protect the brain from swelling after an injury - and allow the body to heal. The patient receives a controlled dose of an anesthetic, which causes lack of feeling or awareness. Doctors then closely watch the person’s vitals. This happens only in hospital intensive care units.


Treatment for a coma depends on the cause. People close to the comatose patient should give doctors as much information as possible to help the doctors determine the cause of coma. Prompt medical attention is vital to treat potentially reversible conditions. For example, if there is an infection that's affecting the brain, antibiotics may be needed. Glucose may be required in the event of a diabetic shock. Surgery may also be necessary to relieve the pressure on the brain due to swelling or to remove a tumor.

Certain drugs may also help relieve the swelling. Medication may also be given to stop seizures if necessary.

In general, treatment for a coma is supportive. People in comas are looked after in an intensive care unit and may often require full life support until their situation improves.

The prognosis for a coma varies with each situation. The chances of a person's recovery depend on the cause of the coma, whether the problem can be corrected, and the duration of the coma. If the problem can be resolved, the person can often return to their original level of functioning. Sometimes, though, if the brain damage is severe, a person may be permanently disabled or never regain consciousness.

Comas that result from drug poisonings have a high rate of recovery if prompt medical attention is received. Comas that result from head injuries tend to have a higher rate of recovery than comas related to lack of oxygen.

It can be very difficult to predict recovery when a person is a coma. Every person is different and it is best to consult with your doctor. As we would expect, the longer a person is in a coma, the worse the prognosis. Even so, many patients can wake up after many weeks in a coma. However, they may have significant disabilities.

Show Sources


Brain Injury Association of America: "What is a Brain Injury?"

National Institute of Neurological Diseases and Stroke: "Coma and Persistent Vegetative State;" "Traumatic Brain Injury;" and "Locked In Syndrome Information Page."

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