Brain death


Brain death (also known as brain stem death) is when a person on an artificial life support machine no longer has any brain functions. This means they will not regain consciousness or be able to breathe without support.

A person who is brain dead is legally confirmed as dead. They have no chance of recovery because their body is unable to survive without artificial life support.

Brain death is legal death

If someone is brain dead, the damage is irreversible and, according to UK law, the person has died.

It can be confusing to be told someone has brain death, because their life support machine will keep their heart beating and their chest will still rise and fall with every breath from the ventilator.

But they will not ever regain consciousness or start breathing on their own again. They have already died.

The brain stem

The brain stem is the lower part of the brain that's connected to the spinal cord (part of the central nervous system in the spinal column).

The brain stem is responsible for regulating most of the body's automatic functions that are essential for life.

These include:

  • breathing
  • heartbeat
  • blood pressure
  • swallowing

The brain stem also relays information to and from the brain to the rest of the body, so it plays an important role in the brain’s core functions, such as consciousness, awareness and movement.

After brain death, it's not possible for someone to remain conscious.

Causes of brain death

Brain death can happen when the blood and/or oxygen supply to the brain is stopped.

This can be caused by:

  • cardiac arrest – when the heart stops beating and the brain is starved of oxygen
  • a heart attack – when the blood supply to the heart is suddenly blocked
  • a stroke – when the blood supply to the brain is blocked or interrupted
  • a blood clot – a blockage in a blood vessel that disturbs or blocks the flow of blood around your body

Brain death can also be cause by:

Brain death is different from vegetative state

The difference between brain death and a vegetative state (a disorder of consciousness), which can happen after extensive brain damage, is that it's possible to recover from a vegetative state, but brain death is permanent.

Someone in a vegetative state still has a functioning brain stem, which means:

  • some form of consciousness may exist
  • breathing unaided is usually possible
  • there's a slim chance of recovery because the brain stem's core functions may be unaffected

Someone in a vegetative state is awake but shows no signs of awareness. For example, they may open their eyes but not respond to their surroundings.

In rare cases, a person in a vegetative state may show some sense of response that can be detected using a brain scan, but not be able to interact with their surroundings.

Tests to confirm brain death

Although rare, a few things can make it appear as though someone is brain dead.

These include drug overdoses (particularly from barbiturates) and severe hypothermia.

A number of tests are carried out to check that brain death, such as shining a torch into both eyes to see if they react to the light.

Organ donation

After brain death, it may be possible for the person's organs to be used in transplants, which can often save the lives of others.

In Wales, since 1st December 2016, there has been a soft opt out system for organ and tissue donation. Unless a person has registered an option to opt-out, it is assumed that he or she has no objection to being an organ donor. This is called deemed consent.

Read more about organ donation.


There are a number of criteria for diagnosing brain death.

For a diagnosis of brain death:

  • a person must be unconscious and fail to respond to outside stimulation
  • a person's heartbeat and breathing can only be maintained using a ventilator
  • there must be clear evidence that serious brain damage has occurred and it cannot be cured

Ruling out other conditions

Before testing for brain death can begin, doctors must carry out a series of checks to ensure that the symptoms are not being caused by other factors, such as:

  • an overdose of illegal drugs, tranquillisers, poisons or other chemical agents
  • an abnormally low body temperature (hypothermia)
  • severe underactivity of the thyroid gland

Once these have been ruled out, tests are carried out to confirm brain death.

The diagnosis of brain death has to be made by 2 doctors, and at least 1 of them must be a senior doctor. Neither of them can be involved with the hospital's transplant team.

The doctors will explain the tests to you and keep you informed about your loved one's condition at all times.

Tests for brain death

The doctors will run a series of tests. Both of doctors have to agree on the results for a diagnosis of brain death to be confirmed.

The tests are carried out twice to minimise any chance of error.

The tests used to determine brain stem death are:

  • a torch is shone into both eyes to see if they react to the light
  • the eye, which is usually very sensitive, is stroked with a tissue or piece of cotton wool to see if it reacts
  • pressure is applied to the forehead and the nose is pinched to see if there is any movement in response
  • ice-cold water is inserted into each ear, which would usually cause the eyes to move.
  • a thin plastic tube is placed down the windpipe to see if it provokes gagging or coughing.
  • the person is disconnected from the ventilator for a short period of time to see if they make any attempt to breathe on their own

Brain death will be diagnosed if a person fails to respond to all of these tests.

Occasionally, a person’s limbs or torso (the upper part of the body) may move after brain stem death.

These movements are spinal relexes and don't involve the brain at all. They will not change the diagnosis of brain death.

The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website
Last Updated: 13/12/2022 14:26:27