What is brain death? How is it diagnosed?

John Henrique Nov 8, 2020

Brain death can be defined as the complete and irreversible loss of all brain functions. It is a legal definition of death.

What is brain death?

Brain death occurs when there is no longer any type of brain activity, be it electrical (from micro impulses between neurons), circulatory, or metabolic (the use of oxygen, glucose, and other nutrients by brain cells).

However, to be defined as brain death, this halt of activities must be irreversible.

From the legal point of view, this is the main definition of death, as it classifies the end of life even though the heart or lungs can be kept functioning with the help of life-support machines or drugs.

However, even with the brain no longer functioning, the spinal cord can still perform some functions, operating the so-called autonomic nervous system, which works unconsciously, so the body may still have a few reflexes and some organs may still be functioning.

What causes brain death?

Brain death is the result of decompensation of the mechanisms that regulate intracranial pressure and cerebral blood flow.

For example, trauma caused by a strong blow to the head increases intracranial pressure. Consequently, the heart fails to pump blood to the brain, since the pressure in the skull is higher.

When the brain is deprived of blood, it loses its functions, resulting in the stopping of brain activity.

The absence of brain activity is brain death.

Brain death can be caused by serious accidents such as head injuries, strokes, intracranial hemorrhages, among others. The most common causes are:

  • Strokes;
  • Head injuries (which may result from accidents);
  • Brain tumors;
  • Infections such as meningoencephalitis;
  • Alcoholic coma;
  • Heart attack;
  • Cerebral hemorrhage.

What is the difference between brain death and coma?

When the patient is in a coma, there is still brain activity and blood flow to the brain. In the case of brain death, there is no brain activity.

How is brain death identified?

The diagnosis of brain death is confirmed in stages. Because it is a devastating and irreversible diagnosis, there is no room for error.

First, the doctor must exclude factors that may be making brain activity imperceptible, such as:

  • Hypothermia: when body temperature is below 34 degrees Celsius, the body reduces brain activity as a form of protection;
  • Metabolic disorders: some diseases can also reduce brain activity;
  • Use of sedatives: anesthetics and some types of medication such as barbiturates can also lead to a decrease in brain activity.

Once these hypotheses are eliminated, the doctor performs a clinical examination that includes the following tests:

  • Pupillary light reflex: with the aid of a flashlight, the doctor checks whether the pupil reacts to light;
  • Corneal reflex: by touching the patient’s cornea, the specialist checks whether it reacts or blinks;
  • Oculomotor test: keeping the patient’s eyes open, the doctor moves his head to see if there is any eye movement;
  • Caloric reflex test: a small amount of cold water is injected into the patient’s ear to check if there is any eye movement in the direction of this stimulus;
  • Painful stimulus: the doctor taps the patient’s forehead, jaw joint, or nails, expecting some reaction to pain;
  • Cough reflex: the trachea is aspirated to check whether the patient coughs involuntarily;
  • Apnea test: the ventilator that keeps the patient breathing is turned off for 10 minutes and experts measure some parameters, such as the level of carbon dioxide in the blood, that indicate whether he is breathing on his own.

If the patient does not react to any of these tests, it is still necessary to prove brain inactivity with at least one of these tests:

  • Electroencephalogram, which detects electrical activity in the brain;
  • Transcranial Doppler, a type of ultrasonography that allows the observation of blood flow in the arteries;
  • Digital subtraction angiography, which shows the arteries of the brain.

The diagnosis needs to be made by two different doctors, who do not necessarily have to be neurologists, in an interval of time ranging from six to 24 hours, or up to 48 hours in the case of children.

When are the machines turned off?

The machines are turned off after the family is informed. If the patient is an organ donor, the machines are kept on long enough to remove the donated organs.

Does brain death leave the person immobile?

Not necessarily. Some people may experience spinal cord reflexes or muscle contractions, but these spinal reflexes have nothing to do with brain activity.

They indicate that the spinal cord is intact. The tests used to diagnose brain death can spot the difference.

Is brain death reversible?

No. A person with brain death is considered legally dead, and the machines that maintain breathing and heart rate will be turned off if the patient is not a donor.

Is brain death equivalent to death?

Yes. Since there is no brain activity, the heart is beating and the body is breathing with the help of artificial life support machines, and this is a situation that will only be maintained artificially.

When is it possible to donate the organs?

When brain death is confirmed, organs can be donated if they are still functional and in good shape, if the family authorizes it.

How is the person kept “alive” until the organs are removed?

The body is connected to a machine called a “ventilator”, which is next to the bed and connected to the patient through a tube in the trachea.

The person is kept on the ventilator and receiving medication until the diagnosis of brain death is confirmed, and a decision is made regarding organ donation.

If the patient is an organ donor, he or she is kept on the ventilator and medication used to control blood pressure and body temperature is administered until the organs are removed. After the removal of the organs, the body is closed and legal burial procedures begin.

What happens if the organs are not donated?

If the organs are not donated, the medical team turns off the machines, signs brain death as the cause of death, with the protocol completion time, and releases the body for burial.

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Related topics:

Brain Brain activity Brain death

Written by John Henrique

John has a degree in IT and is the founder of Hyperaxion. He is a science enthusiast and can usually be found reading a book, stargazing, or playing video games.


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