Brain stem death is where a person no longer has any activity in their brain stem, and has permanently lost the potential for consciousness and the capacity to breathe.
This may happen even when a ventilator is keeping the person's heart beating and oxygen is circulating through their blood.
A person is confirmed as being dead when their brain stem function is permanently lost.
Confirming death used to be straightforward. Death was said to occur when the heart stopped beating and a person was unresponsive and no longer breathing. The lack of oxygen, which occurred as a result of no blood flow, quickly led to the permanent loss of brain stem function.
Confirming death is now more complex, because it's possible to keep the heart beating after the brain stem has permanently stopped functioning. This can be done by keeping a person on a ventilator, which allows the body and heart to be artificially oxygenated.
However, once the brain stem has permanently stopped functioning, there's no way of reversing it and the heart will eventually stop beating, even if a ventilator continues to be used.
To save a person's family and friends from unnecessary suffering, once there's clear evidence that brain death has occurred, the person will be disconnected from the ventilator.
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:
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. Combined with the inability to breathe or maintain bodily functions, this constitutes the death of a person.
How brain death occurs
Brain death can occur 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
heart attack – a serious medical emergency that occurs when the blood supply to the heart is suddenly blocked
stroke – a serious medical emergency that occurs when the blood supply to the brain is blocked or interrupted
blood clot – a blockage in a blood vessel that disturbs or blocks the flow of blood around your body
Brain death can also occur as a result of:
a severe head injury
a brain haemorrhage
infections, such as encephalitis – a viral brain infection
a brain tumour – when brain cells multiply abnormally and uncontrollably
There's a difference between brain death and a vegetative state, which can occur after extensive brain damage.
Someone in a vegetative state can show signs of wakefulness – for example, they may open their eyes, but not respond to their surroundings.
In rare cases, a person may demonstrate some sense of response that can be detected using a brain scan, but not be able to interact with their surroundings.
However, the important difference between brain death and a vegetative state is that someone in a vegetative state still has a functioning brain stem, which means that:
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
A person who is brain dead has no chance of recovery, because their body is unable to survive without artificial support.
Confirming 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 (where body temperature drops below 28°C).
Therefore, a number of tests are carried out to check that brain death has actually occurred, such as shining a torch into both eyes to see if they react to the light.
After brain death has occurred, it may be possible to remove organs from the body that can be used in life-saving procedures, such as a heart-lung transplant.
In cases where a deceased person hasn't made their wishes clear, deciding whether to donate their organs can be a difficult decision for partners and relatives. Hospital staff are aware of these difficulties and will try to ensure the issue is handled sensitively and thoughtfully.
Death is confirmed when a person's brain stem function is permanently lost
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Diagnosing brain stem death
There are a number of criteria for diagnosing brain stem death.
For a diagnosis of brain stem death to be made:
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 can't be cured.
Ruling out other conditions
Before testing for brain stem death can begin, doctors must carry out a series of checks to ensure that the symptoms aren't being caused by other factors. For example:
An overdose of illegal drugs, tranquillisers, poisons or other chemical agents.
An abnormally low body temperature (hypothermia).
A condition that can affect the metabolism (the process that turns food into energy), such as diabetes or liver disease, which can be connected to alcohol misuse (alcoholic liver disease) and obesity (non-alcoholic fatty liver disease).
Once these factors have been ruled out, tests are carried out to confirm brain death. The diagnosis of brain 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 they will keep you informed about your loved one's condition at all times.
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 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 usually very sensitive, is stroked with a tissue or piece of cotton wool to see if the eye 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 trachea (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, even after brain stem death has been diagnosed.
These spinal reflex movements are generated by the spinal cord and don't involve the brain at all. Therefore, they won't affect the diagnosis of brain death.
Has brain stem death ever been incorrectly diagnosed?
From the available evidence, the answer is no.
In 2010, American researchers checked all available medical literature to see if there has ever been a case of a person recovering after a diagnosis of brain stem death. They were unable to find a single case.
Before life support equipment such as ventilators were used, people with brain death would always die within minutes.
Nowadays it's possible to keep oxygen-rich blood circulating inside the body for some time using life support equipment and procedures.
The ventilator and medications supporting blood pressure will usually be discontinued once brain death is diagnosed.
After a person has died, it may be possible for their organs to be used in transplantations, which can often save the lives of others.
If the deceased person carried an organ donor card, signed the Organ Donor Register or had otherwise consented to a transplant before brain death occurred, there's no legal requirement for the transplant team to obtain consent from a partner or relative.
However, in practice, the transplant team will always seek consent from the deceased person's next of kin, and most hospitals won't carry out a transplant if the person's partner or relatives have strong objections to organ donation going ahead.
If the deceased person had not made their feelings about organ transplants known, hospital staff have to make reasonable enquiries to check that:
the deceased person had not expressed an objection to their organs being used in this way after their death
there are no objections from a spouse, partner or relatives
there are no religious reasons why organ donation can't go ahead (all the major religions in the UK support the principle of organ donation)
It can be difficult for partners and relatives to decide whether to donate a loved one's organs to someone who needs an organ transplant.
Hospital staff are aware of these difficulties and will try to ensure the issue is handled sensitively and thoughtfully.