A beating heart and breathing are synonymous with life. However, the moment of actual death may not necessarily be the moment when the heart stops beating, or when breathing ceases. In the case of a brain injury, death may in fact occur hours before the heart stops beating.
Relatives often find the concept of brain death difficult to grasp. How can a person (often young and usually brain-damaged, due to a sudden traumatic incident or accident) who is lying so peacefully in the ICU, whose heartbeat can be seen and heard on the monitor screen, possibly be dead? What about the fact that this person is still breathing, even if it is with the help of a ventilator? How can a doctor be sure that this person's brain is really dead, and that he/she won’t ever wake up?
These fears are real and relevant. Many people don’t want to become organ donors, because they fear that they might be pronounced dead too early.
Some of these fears should be allayed by the requirement that two experienced doctors (one doctor with at least five years of experience - preferably a neurologist or neurosurgeon) are obliged to carry out a series of medical tests independently and according to international criteria. The results of all these tests should be "negative" for any sign of brain activity.
These tests are only carried out when death is not obvious.
When doctors use the term "brain death", they actually are referring to the death of the brain stem, which controls functions such as breathing and circulation. When the brain stem ceases to function, life cannot continue. Brain-stem death usually results from a severe brain injury, which causes all brain activity to stop. The most common causes of these types of brain injury are road accidents, gunshot wounds, stab wounds or strokes.
A patient who is brain dead cannot recover.
How do doctors determine brain death?
First of all, the doctors have to make sure that the coma is not the result of medication, metabolic or endocrine disturbances, or hypothermia (a very low body temperature due to exposure to extreme cold). They do this by scrutinising the patient's medical history, and doing blood tests.
If the patient has taken or been administered a drug that might lead to drowsiness, doctors have to wait for the effect of the drug to wear off and then repeat all the prescribed tests.
Before any tests are conducted, doctors need to identify the possible cause (such as trauma) of brain stem death. An electroencephalogram (EEG) can be done to determine if there is any electrical activity present in the brain. But it is not sufficient to prove brain death.
"The international criteria for brain stem death consist of two major steps," explains Dr Susan Vosloo, heart surgeon with a special interest in heart transplantation.
Firstly, all of the following reflexes must be absent:
- Absent pupil reflex: fixed dilated pupils not constricting when light is shone directly on the eye;
- No cornea reflex: the eyes and eyelids don’t move when touched with a piece of gauze;
- No eye movement when cold water is put in the ears. A doctor puts 20ml of ice water on the eardrums, and watches the patient’s eyes carefully. If the eyes move, the patient isn’t brain dead;
- No movements in the face will be detected when a painful stimulus is applied to different areas of the body;
- The gag reflex is absent: no gagging motion when slight pressure is applied to the throat;
- The coughing reflex is absent when the ventilation tube in the throat is inserted or removed;
- No pain reflex or any sign that the patient experiences pain when the doctor hurts his face;
- No eye movement when the patient's head is being turned from side to side.
The final and critical test is when no breathing movements are detected when the patient is disconnected from the ventilator. Absence of breathing is confirmed by doing a blood test that measures the carbon dioxide and oxygen levels in the blood. If the patient’s carbon dioxide levels in the blood increase, without a breathing reflex being triggered, the brain stem is dead. At even the slightest sign of spontaneous breathing – even a single breath – doctors may not declare a person as being brain dead.
If any of the reflexes are present, doctors will regard the patient as being comatose or in a permanent vegetative state (PVS), but not dead. Patients in a coma – which rarely lasts more than two to four weeks – may emerge from the coma with a combination of physical, intellectual and psychological difficulties, or may slip into a PVS and remain as such for years or decades. In most cases, infection claims the lives of people with PVS.
"If the dead person’s organs are to be used for transplantation, doctors can keep the person on a ventilator, and stable (by administering fluids) for up to 18 hours. In some cases, doctors need to administer hormones to prevent the organs from starting to 'switch off', as this process of deterioration begins as soon as the brain stem dies. Even though machines can keep the blood circulating after brain-stem death, organs will stop functioning within 12 to 24 hours without addition of fluids or hormones," says Dr Vosloo.
- (Mari Hudson, Health24, updated December 2008)