Brain stem death is when a person no longer has any brain stem functions, and has permanently lost the potential for consciousness and the capacity to breathe.
When this happens, a ventilator keeps the person's heart beating and oxygen circulating through their bloodstream.
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, that person won't ever regain consciousness or start breathing again.
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:
- blood pressure
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.
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:
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 28C).
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 for the person's organs to be used in transplantations, which can often save the lives of others.
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.
Read more about organ donation