A coma is a deep state of unconsciousness. It can happen as a result of a traumatic accident, such as a blow to the head, or a medical condition, for example, some types of infection.

Coma is different from sleep because the person is unable to wake up.

It is not the same as brain death. The person is alive, but they cannot respond in the normal way to their environment.

Whether or not they are conscious, or how many people are conscious during a coma, or the level of consciousness, is a question that scientists are currently investigating.

Levels of consciousness and responsiveness will depend on how much of the brain is functioning. A coma often lasts for a few days or weeks. Rarely, it can last for several years.

If a person enters a coma, this is a medical emergency. Rapid action may be needed to preserve life and brain function.

Fact facts on coma

  • During a coma, a person does not react to external stimuli and they will not show normal reflex responses.
  • Comatose patients do not have sleep-wake cycles.
  • Reasons for a coma include intoxication, nervous system disease, metabolic disease, infections, or a stroke.
  • Depending on the cause and the extent of damage, a coma can occur rapidly or gradually, and it can last from several days to several years, though most last from days to weeks.

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A coma is a state of deep unconsciousness.

A person who is experiencing a coma cannot be awakened, and they do not react to the surrounding environment. They do not respond to pain, light, or sound in the usual way, and they do not make voluntary actions.

Although they do not wake up, their body follows normal sleep patterns. Automatic functions, such as breathing and circulation, normally continue to function, but the person's thinking ability is suppressed.

According to the National Institutes of Neurological Disorders and Stroke (NINDS), the person may sometimes grimace, laugh, or cry as a reflex.

Coma may occur for various reasons, such as intoxication, a disease or infection that affects the central nervous system (CNS), a serious injury, and hypoxia, or oxygen deprivation.

Sometimes, a doctor will induce a coma using medications, for example, to protect the patient from intense pain during a healing process, or to preserve higher brain function following another form of brain trauma.

A coma does not usually last for more than a few weeks. If the patient's condition does not change after an extended period, it may be reclassified as a persistent vegetative state.

If a persistent vegetative state lasts for months, the person is unlikely to wake up.

During a coma, a person cannot communicate, so diagnosis is through the outward signs.

These include:

  • closed eyes
  • limbs that do not respond or voluntarily move, except for reflex movements
  • lack of response to painful stimuli, except for reflex movements

How long these will take to develop, and how long they will continue, depend on the underlying cause.

Before entering a coma, a person with worsening hypoglycemia (low blood sugar), or hypercapnia (higher blood CO2 levels), for example, will first experience mild agitation. Without treatment, their ability to think clearly will gradually decrease. Finally, they will lose consciousness.

If a coma results from a severe injury to the brain or a subarachnoid hemorrhage, symptoms may appear suddenly.

Anyone who is with the person should try to remember what occurred just before the coma started, because this information will help determine the underlying cause and give a better idea of what treatment to apply.

Recognizing symptoms

A first responder may start by using the AVPU scale, try to gauge the level of consciousness.

The AVPU scale looks at the following areas:

Alertness: How alert is the person?

Vocal stimuli: Do they respond to another person's voice?

Painful stimuli: Do they respond to pain?

Unconscious: Are they conscious?

Alert is the most conscious state, and unconscious is the least. This helps the health professional assess whether this is likely to be an emergency. If the person is alert, there is no risk of coma.

In the hospital, doctors may apply the Glasgow coma scale (GCS) to assess the person's condition in more detail.

Patients with deep unconsciousness may be at risk of asphyxiation. They may need medical help to secure the airways and ensure they continue to breathe. This could be a tube that passes through the nose or mouth, into the lungs.

Can a person hear and think when they are in a coma?

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A person in a coma may benefit from sensory stimulation, such as holding a hand.

There is some evidence that people can hear and understand spoken instructions during a coma.

In 2011, neuroscientists using fMRI scanning technology observed brain activity in a man who had been in a coma for 12 years after a road traffic accident.

For example, when they asked the man to imagine he was playing tennis or walking round his house, his brain activity reflected that he was thinking of doing these things.

Scientists now believe that 15 to 20 percent of people in a so-called vegetative state may be fully conscious. Advances in technology mean that we are better able to understand what people are experiencing during a coma.

A person who is visiting a friend or family member who is in a coma can speak to them as they normally would, for example, explaining what has been happening during the day. It is unclear how much they can understand, but there is a chance the person may be able to hear and understand. They may like to listen to music.

Research has also suggested that stimulating the senses of touch, smell, sound, and vision may help the person recover. A visitor could help by wearing a favorite perfume or holding the person's hand.

Causes or a coma vary, but they all involve some level of injury to the brain or CNS.

They include:

Diabetes: If the blood sugar levels of a person with diabetes rise too much, this is known as hyperglycemia. If they become too low, this is hypoglycemia. If hyperglycemia or hypoglycemia continue for too long, a coma can result.

Hypoxia, or lack of oxygen: If the supply of oxygen to the brain is reduced or cut off, for example, during a heart attack, stroke, or near drowning, a coma may result.

Infections: Severe inflammation of the brain, spinal cord, or tissues surrounding the brain can result in coma. Examples include encephalitis or meningitis.

Toxins and drug overdose: Exposure to carbon monoxide can result in brain damage and coma, as can some drug overdoses.

Traumatic brain injuries: Road traffic accidents, sports injuries, and violent attacks that involve a blow to the head can cause coma.

A medical and recent history, blood tests, physical tests, and imaging scans can help find out the cause of a coma, and this helps decide which treatment to apply.

Medical history

Friends, family, police, and witnesses, if appropriate, may be asked:

  • whether the coma or symptoms beforehand started slowly or suddenly
  • if the person had or appeared to have any vision problems, dizziness, stupor or numbness before the coma
  • whether the patient has diabetes, any history of seizures or stroke, or any other condition or disease
  • what medications or other substances the patient may have been taken

Physical tests

The aim is to check the person's reflexes, how they respond to pain, and their pupil size. Tests may involve squirting very cold or warm water into the ear canals.

These tests will trigger varying reflexive eye movements. The type of response varies according to the cause of the coma.

Blood tests

These will be taken to determine:

  • blood count
  • signs of carbon monoxide poisoning
  • presence and levels of legal or illegal drugs or other substances
  • levels of electrolytes
  • glucose levels
  • liver function

Lumbar puncture (spinal tap)

This can check for any infection or disorder of the CNS. The doctor inserts a needle into the patient's spinal canal, measures pressure, and extracts fluid to send for tests.

Imaging scans of the brain

These will help determine whether there is any brain injury or damage, and where. A CT or CAT scan or an MRI will check for blockages or other abnormalities. An electroencephalography (EEG) will measure electrical activity within the brain.

Glasgow Coma Scale

The Glasgow Coma Scale (GCS) can be used to assess the severity of brain damage following a head injury.

It gives patients a score, according to verbal responses, physical responses, and how easily they can open their eyes.

Eyes: Scores range from 1 to 4, where 1 is when a person does not open their eyes, 2 is when they open their eyes in response to pain, 3 is when they open them in response to voice, and 4 is when they open them spontaneously.

Verbal: Scores range from 1 to 5, where 1 means the person makes no sound, 2 means they mumble but cannot be understood, 3 is when they utter inappropriate words, 4 is when they speak but are confused, and 5 is normal communication.

Motor, or physical reflexes: Scores range from 1 to 6, and 1 to 5 describe a person's response to pain. A person who scores 1 makes no movement, 2 is when they straighten a limb in response to pain, 3 is when they react in an unusual way to pain, 4 is when they move away from pain, and 5 is when they can pinpoint where the pain is. A score of 6 means the person can obey commands.

A score of 8 or less overall indicates a coma. If the score is from 9 to 12, the condition is moderate. If the score is 13 or more, the impairment to consciousness is minor.

A coma is a serious medical emergency.

Health professionals will start by ensuring the immediate survival of the patient and securing their breathing and circulation to maximize the amount of oxygen that reaches the brain.

A doctor may administer glucose or antibiotics even before the results of blood tests are ready, in case the patient is in diabetic shock or has a brain infection.

Treatment will depend on the underlying cause of the coma, for example, kidney failure, liver disease, diabetes, poisoning, and so on.

If there is brain swelling, surgery may be needed to relieve the pressure.

If the cause of the coma can be successfully treated, the person may eventually awaken with no permanent damage.

They are likely to be confused at first, but then they usually remember what happened before the coma, and be able to continue their life. Typically, some rehabilitation therapy is necessary.

If brain damage has occurred, long-term impairment may result. If the person awakens, they may need to relearn basic skills, and they may not remember what happened.

However, with support, such as physical and occupational therapy, many people can enjoy a good quality of life.

In some cases, the person will not wake up.

In 2015, neurologists published findings showing that there may be a way to predict when patients will awaken from a coma. During a coma, specific patterns of neuronal communication appear to be disrupted.

Using functional MRI (fMRI) tests, the scientists noticed that patients who retained a particular strength of neuronal communication were more likely to recover from a coma.

This could mean that fMRI might be able to predict a person's likelihood of recovery.

Another study carried out in 2015 found evidence that voices of family members and loved ones could help improve responsiveness in people during a coma. After 15 patients who underwent either familiar auditory sensory training (FAST) or placebo silence, fMRI scans show improvements in the brains of those who experienced FAST.