Brain death occurs when a person in an intensive care unit no longer has any activity in their brain stem, even though a ventilator is keeping their heart beating and oxygen circulating through their blood.

Once a brain stem death has occurred, the person is confirmed dead.

The brain stem

The brain stem is the lower part of the brain that is connected to the spinal cord (a column of nervous tissue located in the spinal column). The brain stem is responsible for regulating most of the automatic functions of the body that are essential for life. These are:

• breathing
• heartbeat
• blood pressure
• swallowing

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

Persistent vegetative state

There is a difference between brain stem death and a persistent vegetative state (PVS), which can occur after extensive damage to the brain. Someone in a PVS is conscious but has no awareness of their surroundings and is incapable of feeling mental distress or physical pain. However, unlike a person with brain death, there is a slim chance that a person with PVS can recover because the core functions of the brain stem are often unaffected.

See the Health A-Z topic about Vegetative state for more information on this condition.

Outlook

Unfortunately, there is no chance of a person recovering once their brain stem has died. This is because all of the core functions of the body have stopped working and can never be restarted. Although a ventilator can keep the heart beating, the person is effectively dead.

If permission has been given, organs can be removed for transplant and ventilation is withdrawn. Once ventilation is withdrawn, the heart stops beating within a few minutes.

Brain stem death can occur when the blood and oxygen supply to the brain is stopped. This can be caused by:

• a heart attack – a serious medical emergency that occurs when the blood supply to the heart is suddenly blocked
• a stroke – a serious medical emergency that occurs when the blood supply to the brain is interrupted
• a blood clot – a blockage in one of your blood vessels that disturbs or blocks the flow of blood around your body

Brain stem death can also occur as a result of:

• a serious head injury
• infections, such as encephalitis (a viral infection of the brain) 
• a brain tumour (a growth of cells multiplying in an abnormal, uncontrollable way in the brain)

A diagnosis of brain stem death is considered when:

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

Ruling out other conditions

Before testing for brain stem death can begin, doctors must carry out a series of checks to make sure that the symptoms are not being caused by other factors. Possible factors include:

• an overdose of illegal drugs, tranquillisers, poisons or other chemical agents
• having an abnormally low body temperature (hypothermia - symptoms)
• having a condition that can affect the metabolism (the process that turns food into energy), such as diabetes (a long-term condition caused by too much glucose in the blood) or liver disease (when the liver is damaged, often through drinking excessive amounts of alcohol)

Once these factors have been ruled out, a number of tests are carried out to confirm the diagnosis. The diagnosis of brain stem death has to be made by two senior doctors. Neither of them can be involved with the hospital's transplant team.

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

Tests

The doctors will run a series of tests. Both of them 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 whether brain stem death has occurred are outlined below:

• a torch is shone into both eyes to see if they react to the light
• the cornea (transparent outer layer of the eye), which is normally very sensitive, is stroked with a tissue or piece of cotton wool
• pressure is applied to the forehead and the nose is pinched to see if there is any movement in response
• ice-cold water is squirted into each ear, which would normally cause the eyes to move
• a thin, plastic tube is place down the trachea (windpipe) to see if this provokes a gagging or coughing reflex
• the person is withdrawn from the ventilator for a short period of time to see if they make any attempt to breathe on their own

If a person fails to respond to all of these tests, a diagnosis of brain stem death is made.

Occasionally, a person’s limbs or their torso (the upper part of their body) may move, even after brain stem death has been diagnosed. These are spinal reflex movements, which means they are generated by the spinal cord and do not involve the brain at all. These movements will not affect the diagnosis of brain stem death.

Before the use of life support machines, people with brain stem death would almost always die within minutes. Today, body cells can be kept alive indefinitely by using life support systems, even when the brain stem is no longer functioning.

This allows doctors to remove organs from somebody who is dead and use them for transplants.

Organ donation

If the deceased person carried an organ donor card, signed the NHS organ donor register, or has otherwise consented to a transplant before the brain stem death occurred, there is no legal requirement for the transplant team to obtain consent from a partner or relative.

However, most primary care trusts (PCTs) will not do a transplant if relatives or a partner have strong objections to a transplant going ahead.

If the deceased person had not made their feelings about organ transplants known, hospital staff have to make reasonable enquires to check that:

• the deceased person had not expressed an objection to their body being used in this way after their death
• there are no objections from a spouse, partner or relatives
• there are no religious reasons why a transplant cannot go ahead

Deciding whether to carry out a transplant can be a difficult decision for partners and relatives. Hospital staff are aware of these difficulties and will ensure that the issue is handled sensitively and thoughtfully.

See the Health A-Z topic on Organ donation for more information on this process.