How is ‘brain death’ different from ‘circulatory death’?
Most people understand that death occurs when a person’s heart and breathing stop. This can also be called circulatory death and it is how most people die. When someone has died a circulatory death, they do not breathe or move, they do not have a heart beat and their skin is cold and dusky.
Death also occurs when the brain and brainstem have stopped working completely – this is called brain death. The kinds of serious injuries which may lead to brain death include accidents where there is trauma to the head, bleeding into the brain, infections or a period of time without oxygen or blood flow to the brain. As part of the treatment for these conditions, the person will be connected to a ventilator, which pushes oxygen into the lungs, causing the chest to rise/fall and sustaining the heartbeat. Despite having a beating heart and a chest that rises and falls, if basic brain functions are absent, determined using specific tests, then death has occurred as a result of brain death. Brain death is not the same as “brain damage, “brain injury,” or “coma”, it is permanent, irrecoverable and as such is equivalent to circulatory death in terms of outcome. Nevertheless this is a difficult concept to understand. Observing the tests and investigations performed can be helpful for relatives in demonstrating the absence of basic brain function in brain death and the reality of death.
What causes the brain to die?
The brain requires a constant supply of oxygen rich blood. Interruption of this supply causes injury and like other parts of the body – the brain swells as a result.
For example, an injured finger or ankle swells, but can keep expanding because there is no restriction. The brain however, is contained within the rigid skull that limits how much it can expand. As the brain continues to swell, pressure builds up within the skull.
This increased pressure within the skull causes permanent irrecoverable damage to the brain:
- Blood vessels supplying the brain get compressed; this stops blood and oxygen flowing to the brain.
- Without the oxygen, brain cells die and cannot recover. This causes even more swelling.
- The swollen brain expands in a downwards direction further injuring the brainstem (where the spinal cord and the brain connect) and this swelling results in injury to the brain stem and brain death.
- The brain stem is fundamental to life - it controls breathing, coughing, heart rate, blood pressure, response to pain and body temperature.
A person who is brain dead cannot and will not breathe. They cannot feel pain and will never feel pain – e.g a cotton wool ball gently touched on their eyeball will not cause blinking. They have not and will not have any awareness of self. They cannot and will not cough, gag, get dizzy, move their eyes or do anything that they have learnt during their lifetime. They have lost all their basic/primitive reflexes and everything more advanced as well.
How can the doctors tell when a person’s brain has died?
There are a number of physical changes in pupil reaction, heart rate, blood pressure and body temperature that are seen with brain death. These changes, together with the loss of other natural responses such as breathing, coughing and blinking, cause doctors to suspect that brain death has occurred. A number of specific tests are then done to find out whether or not the brain is working. Two senior doctors independently perform testing of cranial nerves originating in the brainstem (which control all vital basic brain reflexes). For a person to be declared brain dead there must be no responses to these tests. These tests are done after a number of preconditions are met; following a period of observation and on 2 separate occasions. The doctors will ensure that they are completely certain of the results of these tests prior to making the diagnosis of brain death.
There are times when some patients may not be able to have all of these tests performed. This is maybe due to the nature of the injuries which have been sustained. For example, a spinal injury, an eye injury, or a facial injury will mean those nerves cannot be adequately tested. In these cases, perfusion scans are done to determine if there is any blood flow to the brain. This may be either a cerebral angiogram or a cerebral perfusion scan.
What happens after a person is confirmed to be brain dead?
Once death has been confirmed, appropriate members of the medical team will speak with the family. In the setting of brain death it may be possible for the relatives or family to consider discussing organ donation with the doctors involved.
If organ donation is wanted then a donation specialist will provide information to families about what needs to happen, if donation is not an option the family wish to pursue or there are medical reasons why the person cannot be an organ donor, the medical staff will speak with the family about the timing of removing the ventilator.