What Causes Coma?

Conditions list medically reviewed by George Krucik, MD, MBA

A coma is a prolonged state of unconsciousness. A coma occurs when a part of the brain is damaged, either temporarily or permanently. This damage results in unconsciousness, an inability to awake, and unresponsiveness to stimuli such as pain,... Read More

A coma is a prolonged state of unconsciousness. A coma occurs when a part of the brain is damaged, either temporarily or permanently. This damage results in unconsciousness, an inability to awake, and unresponsiveness to stimuli such as pain, sound, and light. The word “coma” is derived from the Greek word “koma,” which means “deep sleep.”

Comas have a number of potential causes. These range from injury or illness to stroke, to tumors, to alcohol and drug abuse.

A person who is in a coma is alive but is unable to move at will. They can’t think, speak, or respond to their environment. Important functions, such as breathing and blood circulation, remain intact.

A coma is a medical emergency. Healthcare providers need to work quickly to preserve brain life and function. They also need to keep the patient healthy during the course of his or her coma.

A coma may be challenging to diagnose and treat. It usually doesn’t last for more than four weeks, and recovery occurs gradually. Some patients, however, have remained in comas for years or even decades.

What causes a coma?

Comas are caused by damage to the brain, specifically the diffused bilateral cerebral hemisphere cortex or the reticular activating system. This area of the brain controls arousal and awareness. Damage here can result from many potential factors. This includes head injuries, loss of oxygen, bleeding or pressure in the brain, infections, metabolic problems, and toxic factors. Some specific examples include:

  • traumatic brain injuries, such as those caused by traffic accidents or violent fights
  • stroke (reduced blood supply to the brain)
  • tumors in the brain or brainstem
  • lack of oxygen to the brain after being rescued from drowning or from a heart attack
  • diabetes, which causes blood sugar levels to become too high (hyperglycemia) or too low (hypoglycemia) and can lead to swelling in the brain
  • overdosing on drugs or alcohol
  • carbon monoxide poisoning
  • buildup of toxins in the body, such as ammonia, urea, or carbon dioxide
  • heavy metal poisoning like lead
  • infections such as meningitis or encephalitis
  • repeated seizures
  • electrolyte imbalance

What are the symptoms of a coma?

A coma is a medical emergency and requires immediate medical attention. Signs of a coma can include:

  • closed eyes
  • unresponsiveness
  • irregular breathing
  • no response of limbs, except for reflexes
  • no response to pain, except for reflexes
  • pupils not responding to light

How is a coma diagnosed?

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

How is a coma treated?

The first priority of treatment is to preserve brain life and function. Antibiotics may be given right away, in case there is an infection in the brain. Medications for treating the underlying condition will be administered if the cause of the coma is known, as in the case of a drug overdose. Surgery may be required to reduce swelling in the brain.

A team of medical professionals will work with the comatose patient once they are stabilized. They’ll work to prevent infections, bedsores, and contractures of the muscles. The team will also make sure to provide the patient with balanced nutrition during their coma.

What can be expected in the long term?

A coma usually does not last for more than four weeks. Some people may remain in a coma for much longer, however. Long-term outcomes depend on what caused the coma and the site and extent of damage to the brain. The prognosis may be good for people whose comas are caused by a drug overdose. The severity of the brain damage dictates the long-term outcome.

Some people emerge from a coma with physical, intellectual, or psychological problems. Patients who remain in a coma for more than a year are unlikely to come out of that state. Potential complications during a coma include infections, blood clots, and pressure sores.

Medically reviewed by Judith Marcin, MD on November 7, 2016Written by Jacquelyn Cafasso


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This feature is for informational purposes only and should not be used to diagnose. Please consult a healthcare professional if you have health concerns.