A coma is a state of prolonged unconsciousness that can be caused by a variety of problems — traumatic head injury, stroke, brain tumor, drug or alcohol intoxication, or even an underlying illness, such as diabetes or an infection.

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.
  • 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.
  • Persistent vegetative state. This is a state of severe unconsciousness. The person is unaware of his or her 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.
  • Locked-in syndrome. This is a rare neurological condition. The person is totally paralyzed except for the eye muscles, but remains awake and alert and with a normal mind.
  • Brain death. This is an irreversible cessation of all brain function. Brain death may result from any lasting or widespread injury to the brain.
  • Medically induced: This type of temporary coma, or deep state of unconsciousness, is used to protect the brain from swelling after an injury. 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.


The signs and symptoms of a coma commonly include:

  • Closed eyes
  • Depressed brainstem reflexes, such as pupils not responding to light
  • No responses of limbs, except for reflex movements
  • No response to painful stimuli, except for reflex movements
  • Irregular breathing


People in a coma can’t speak or express themselves in other ways. Healthcare providers must rely on information from loved ones or witnesses. They also look for any physical signs that may give information about what caused the coma.

The healthcare provider will ask friends and family about any events or symptoms that led up to the coma. They’ll also ask details about recent changes in the patient’s life, medical history, and drug use. Drugs of concern include prescription drugs and over-the-counter drugs, as well as recreational drugs.

A physical exam will be conducted. This might include:

  • Checking reflexes
  • Observing breathing patterns
  • Checking for signs of bruises on the skin that may have been caused by trauma
  • Determining the patient’s response to painful stimuli
  • Observing pupil size

Blood tests and other laboratory tests will be used to test for the following:

  • Blood count
  • Thyroid and liver function
  • Electrolyte levels
  • Carbon monoxide poisoning
  • Drug overdose
  • Alcohol overdose
  • Infections of the nervous system

Tests may be used in order to create images of the brain (brain scans), to locate areas of brain injury, and to look for signs of brain hemorrhage, tumors, stroke or seizure activity. These tests include:

  • Computerized tomography (CT) scans, which use X-rays to create a detailed image of the brain
  • Magnetic resonance imaging (MRI), which uses radio waves and magnets to view the brain; and
  • Electroencephalography (EEG), which measures electrical activity inside the brain



A coma is a medical emergency. Doctors will first check the affected person’s airway and help maintain breathing (respiration) and circulation. Doctors may give breathing assistance, blood transfusions and other supportive care.

Other treatments may focus on medications or therapies to address an underlying disease, such as diabetes or liver disease.

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