What Is a Coma?

A coma is any condition in which someone is:

  • Unconscious, usually for a long time
  • With their eyes closed
  • Can't be awakened by even vigorous or painful stimulation

A coma is not the same as sleep. In a coma, the brain doesn't go through normal sleep cycles. Someone who is sleeping may move if they're uncomfortable, but a person in a coma can't.

In this article, you'll learn what causes comas, what it takes to recover from a coma, and what some similar states of unconsciousness are.

Patient in intensive care unit
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Coma Causes

By definition, doctors put people into coma every time they use general anesthesia. However, most people wake up after a few hours, once their bodies process the medication.

The definition also includes people who are unconscious due to medications, toxins, or infections. As with anesthesia, they generally wake up when the body rids itself of the substance.

And then there are the forms of coma you hear about more often—the ones it may be impossible to wake up from.

Many types of illnesses and injuries can put someone into that type of coma, including:

Contrary to what many people think, nerve cells can regenerate. But they do so only in specific parts of the brain. Plus, it's a very slow process.

If enough nerve cells die in a region essential for maintaining wakefulness, the person will probably never regain normal consciousness. These regions include:

Recovery

Whether someone can recover from a coma depends on many factors, including what put them there in the first place.

For example, a coma from traumatic brain injury tends to have a better prognosis than a coma from cardiac arrest.

Younger patients tend to do better than older ones. Someone in a drug-induced coma may wake naturally as the drug is cleared from their system.

But someone with a permanent brain lesion may progress to a persistent vegetative state or even brain death.

In general, the longer someone remains unconscious, the less likely they are to recover their alertness.

However, the only way to know for sure whether someone will recover from a coma is to wait for a reasonable amount of time and see.

How much time to wait can be a hard decision. It depends on the unique circumstances of the person and their family. Be sure to discuss these issues with the medical team taking care of them.

Recap

A coma is a condition involving unconsciousness, closed eyes, and an inability to be awakened. Causes include head injury, seizure, brain damage or infection, stroke, drug overdose, or chemical imbalances such as hypoglycemia. If damage is severe enough in certain brain regions, the person is unlikely to ever come out of the coma.

Other States of Unconsciousness

The same injuries and illnesses that put people in a coma can also lead to other states of unconsciousness. The four different states, in order of severity, are:

  • Minimal consciousness
  • Coma
  • Vegetative state
  • Brain death

Minimal Consciousness

Minimal consciousness is a less serious state than a coma. Neurologists often hope for signs that someone is minimally conscious rather than in a true coma or vegetative state.

Minimally conscious people are still largely unaware of what's going on around them. But there is at least some glimmer of preserved awareness of the self or the surrounding environment.

This may mean:

  • A consistent ability to follow simple commands
  • Appropriately give yes/no responses
  • Demonstrating purposeful behavior (appropriate smiling or crying, adjusting their hands to the size and shape of held objects)

In general, people in minimally conscious states have much better outcomes than those in sustained comas.

A comatose person may move in ways that seem like they are awake, misleading friends and family. For example, they may grimace if something causes pain.

They may even appear to move away from pain. In what's called Lazarus syndrome, an especially strong reflex can lead someone in a coma to sit upright.

However, these responses are just reflexes. It's similar to what happens to your leg when a healthcare provider taps your knee with a hammer. These movements don't mean someone is awake or aware.

Outcomes tend to be better for people in a minimally conscious state than those in a coma or worse. Even so, many people who recover from this state remain seriously disabled.

Vegetative State

Whereas comatose patients appear to be sleeping, people in a vegetative state regain some degree of crude arousal, resulting in the eyes being open.

The eyes may even reflexively move, appearing to gaze at things in the room. However, these people don't show any true awareness of themselves or their environment.

If the brainstem remains intact, the heart, lungs, and gastrointestinal tract continue to function. If not, machines may be needed to keep these functions going.

If this condition lasts for months, or if someone is in a coma for several weeks, they're considered to be in a persistent vegetative state.

This can be permanent. If medical care continues, it's possible for someone to remain alive in a persistent vegetative state for decades.

Brain Death

Brain death is an even more severe situation. It occurs when brainstem function is compromised in someone who's comatose and they can no longer breathe on their own. If machine support is removed, they'll typically go into cardiac arrest.

There are no well-documented cases of meaningful recovery in people accurately diagnosed with brain death.

While a qualified physician can make a diagnosis of brain death based on the physical exam alone, given the seriousness of the diagnosis, some families prefer to have additional tests done as well.

However, if the bedside exam can be done completely and accurately, additional tests are unlikely to show any new or more hopeful information. Autopsies generally show that much of the brain has wasted away.

Recap

Minimally conscious people may be able to respond to questions and follow simple directions.

Someone in a vegetative state may appear more aware than someone in a coma, but they're not. After several weeks, it's considered a persistent vegetative state, which can be permanent.

Brain death occurs when someone who's comatose will die without machine support.

Summary

A coma is a state of unconsciousness you can't be awakened from. The brain doesn't go through normal sleep cycles and you can't move in response to pain. Comas are caused by brain damage from head injuries or illness.

If damage is in the thalamus, brainstem, or cerebral cortex, recovery may not be possible. Recovery depends on many other factors, as well, including age and the cause of the coma. The longer it lasts, the less likely recovery is.

Minimal consciousness is less severe than a coma. People retain some awareness and ability to respond. A vegetative state is more severe than a coma. If it lasts for weeks, it's called a persistent vegetative state. Brain death means the person can no longer survive without life-support equipment.

A Word From Verywell

If someone you care about is in a state of unconsciousness, ask their medical team what state they're in and what kind of awareness they may have.

Understanding the different possible states may influence your actions around the unconscious person and help guide your decisions regarding their care.

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8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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