There are a number of criteria for diagnosing brain death.

For a diagnosis of brain death:

• 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 cannot be cured

Before testing for brain death can begin, doctors must carry out a series of checks to ensure that the symptoms are not being caused by other factors, such as:

• an overdose of illegal drugs, tranquillisers, poisons or other chemical agents
• an abnormally low body temperature (hypothermia)
• severe underactivity of the thyroid gland

Once these have been ruled out, tests are carried out to confirm brain death.

The diagnosis of brain death has to be made by 2 doctors, and at least 1 of them must be a senior doctor. Neither of them can be involved with the hospital's transplant team.

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

The doctors will run a series of tests. Both 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 brain stem death are:

• a torch is shone into both eyes to see if they react to the light
• the eye, which is usually very sensitive, is stroked with a tissue or piece of cotton wool to see if it reacts
• pressure is applied to the forehead and the nose is pinched to see if there's 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 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 is 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 after brain stem death.

These movements are spinal reflexes and do not involve the brain at all. They will not change the diagnosis of brain death.