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What is brain death? Is it irreversible?

What is brain death? Is it irreversible?

November 16, 2022

When we think about death, we usually think of a more or less prolonged process in which little by little our heart stops beating and our lungs stop working. The term expire to refer to death or expressions like exhaling the last breath are a clear reference to this way of seeing death.

However, nowadays it is known that it is possible that the cardiorespiratory functions stop and still can be kept alive thanks to mechanical supports. However, there is another aspect that definitively reflects the death of a person as such, and the end of brain activity. We are talking about brain death .

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What is brain death?

It is considered that the brain death of a person occurs when the Complete and irreversible cessation of all brain functions , both on the part of the hemispheres and the brain stem. It is important to take into account the nuances of complete and irreversible, since different types of brain injuries are capable of causing similar symptoms that may be recoverable or suppose only a partial cessation of functions. Thus, in order to diagnose a brain death, it is necessary to certify that there is no possibility of recovery, and for this, it is necessary to carry out confirmatory tests and the application of highly systematized protocols.


Brain death is usually caused by massive brain injuries, especially when the brainstem is injured (responsible for regulating aspects such as breathing and heartbeat). One of the most frequent causes of brain death occurs when the intracranial pressure exceeds the systolic blood pressure, which culminates in the cessation of blood circulation in the brain. In this state the blood, usually loaded with oxygen and nutrients, does not reach the brain and therefore it ceases to function because of hypoxia.

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Diagnosis: key aspects to check

Diagnosing brain death is not easy , and for this it is necessary to prove the nonexistence of different brain functions through different protocols. Specifically, it stipulates that at least two different specialized doctors must perform the patient's examination, performing at least two physical examinations and two electroencephalograms separated in time.


In the case of children under one year of age, the observation period is usually longer, requiring a higher level of verification and more repetitions of these, as their brain is more immature and it is more expensive to perform the neurological examination.

To diagnose brain death, it is essential to take into account if the subject is in conditions that allow such verification. For this, the organism must possess a respiratory cardiac stability, either naturally or through artificial mechanisms, an adequate blood oxygenation level and a temperature level that reflects the absence of hypothermia (which can cause symptoms similar to brain death). In this last aspect the body has to be at least more than 32º C.

As well it is necessary to rule out that the organism is in a state of intoxication due to drugs or under the effects of psychotropic drugs, since some substances can cause apparent death, and even many substances of a psycholeptic or depressant type can be misleading by avoiding responses to different stimulations. Conditions due to metabolic problems, such as insulin coma, should also be ruled out.


Once these aspects prior to the neurological analysis are taken into account, the following aspects can be analyzed.

1. Irreversible and irreversible coma state

In order to diagnose brain death, the subject must be in a coma due to a known cause and well established (discarding aspects such as the ones mentioned above of hypothermia or intoxication, for example). One of the main aspects to verify is that the subject in question does not have any kind of reaction to the stimulation. To verify this, the application of painful stimuli such as activation of the trigeminal nerve is used, and neither vegetative nor motor reactions should occur.

2. Brain activity: flat encephalogram

Through the encephalogram cerebral bioelectrical activity is measured . In this way, that it appears flat indicates that no brain activity is recorded, showing that the central nervous system has stopped acting. In addition to the encephalogram, many other neuroimaging techniques can be used to check brain activity, such as evoked potentials or various types of computed tomography.

3.Respiratory functions dependent on artificial elements

One of the aspects that are proven when establishing the brain death of a person is that they are not able to breathe on their own. To do this, the apnea test is used , through which the artificial respiration is temporarily stopped (having previously oxygenated the blood) to observe if the individual breathes by itself through the observation of respiratory movements and the measurement of the partial pressure of carbon dioxide in the blood of the arteries (paCO2).

If no respiratory movements are observed and paCO2 exceeds 60 mmHg (which indicates the maximum stimulation of the respiratory centers), it is considered that the test gives a positive result in indicating the absence of breathing, reconnecting the subject to respiration artificial.

4. Absence of own cardiac functions

To check that the heart does not work on its own without mechanical aid, the atropine test is applied, injecting into the blood supply the substance that gives the test its name. In subjects with their own heart rate, said injection would suppose an increase and acceleration of the cardiac rate, with which the absence of reaction is a negative indicator.

5. Absence of reflexes derived from the brainstem

When the brain dies, the different reflexes and typical reactions to the different types of stimuli cease to appear. The brain stem is the area of ​​the brain that regulates the most basic aspects and functions for life, so that the reflexes that are developed in this area suppose some of the most basic, with what its absence suggests the existence of brain death.

One of the reflections to explore is the photomotor reflection , that is to say if the eye presents / displays pupillary reaction to the level of light (for example focusing a flashlight directly to the pupil). In case of brain death, there should not be any type of reaction to light stimulation.

Another one of the reflexes to take into account is the corneal, in which it is observed if there is a reaction to pain and friction through tactile stimulation through the use of gauze. It also proceeds to introduce cold liquids in the ear, which in brain-active subjects would cause a reaction in the form of eye movement (oculovestibular reflex). The oculocephalic reflex is also checked , turning the patient's head horizontally quickly to check if there is any type of eye movement

Apart from the reflexes of the oculomotor system, there is also evidence of the existence of reflexes linked to the nerves that govern the mouth and digestive tract. For example, it is intended to provoke nausea by stimulating the palate and the phalanx. The trachea is also stimulated in order to try to elicit responses in the form of cough or nausea. In any of the cases, if we are dealing with a case of brain death, there should not be any type of reaction.

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The confusion between brain death and other concepts

Brain death is a concept that, although it may be easy to understand at first, is often confused with other terms. The most frequent of all of them is the concept of coma.

Although a coma can end up leading to the brain death of the subject and in fact for the diagnosis of it is usually required that the patient has entered an irreversible coma, the latter is not identified with brain death.

The patient in a coma, although remains unconscious and is in many cases unable to respond to stimuli, continues to have a certain level of brain activity which means that he can still be considered alive even if vital support is needed to make his heart continue to pump blood and artificial respiration. Although it is not always reversible in many cases, this possibility exists. People who leave this state usually do so between the first two and four weeks, but in some cases the coma can last up to several decades.

Another related aspect can be found in the confinement syndrome . In this strange syndrome the subject does not present any type of stimulating reaction, but nevertheless he is fully aware of what is happening around him. In some cases they may move their eyes. It is usually caused by damage to the brainstem resulting from injuries in it, overdose or problems or vascular accidents.

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Contradictory cases: returning from the dead

As we have seen, one of the main characteristics of brain death is its irreversibility. The diagnosis is made once there have been very rigorous, systematic and strict checks. However, although it is not very common, some cases of people who have been considered brain dead and who have subsequently been reanimated .

The explanation of this phenomenon seems simple: although it is possible, it is extremely complicated to assert that a brain is unrecoverable, as in some cases derived from hypothermia or substance use.In this way, some people who were not brain dead yet may have been incorrectly diagnosed.

Some of the possible causes of said poor diagnosis may be due to the alteration of the tests carried out due to not taking into account certain conditions of the subject (state of shock, hypothermia, consumption of medications or metabolic disorders) or confusion with conditions similar to brain death but without reaching it.

It could be possible to find that the brain dies for a short period of time and that it manages to recover the patient if the reason for the cessation of functioning is reversible and reactivates the brain, but in principle brain death conceptually assumes that there is an irreversibility in that state. So at least at present (although it does not seem likely in the future, scientific research may find ways to recover the functionality of a brain that is already dead if it is preserved) brain death means the end of life as such .

Organ donation

Once the brain death of the patient is diagnosed, you can proceed to the disconnection of artificial life support . However, if the patient has wanted to donate the organs or their relatives have given permission to do so, these organs can be extracted and transplanted, including those organs that have been artificially maintained, such as the heart.

In this aspect we must bear in mind that the donation of some of them is only possible if the organ remains in operation, having to be transplanted directly after the death while the organ remains alive.

The relative absence of life

The phenomenon of brain death not only tells us that the most important component to determine if a person is alive or not in brain activity .

In addition, it shows that the line that separates life from death is not as clear as one might think in a moment, and that it is something relative. If you had the right technical means, it would be possible to revive practically any person as long as the brain tissues did not deteriorate and a way to reactivate several groups of relevant neurons was found at the same time. Neither the absence of heartbeats is the objective signal that someone has left to not return, nor does it make sense that it is.

Bibliographic references:

  • Escudero, D. (2009). Diagnosis of encephalic death. Medicina Intensiva vol.33, 4. Intensive Medicine Service. Central University Hospital of Asturias.
  • Racine, E .; Amaram, R .; Seidler, M .; Karczewska, M. & Illes, J. (2008). Media coverage of the persistent vegetative state and end-of-lif e decision-making. Neurology, 23; 71 (13): 1027-32.
  • Wijdicks, E.F.M. (2001). The diagnosis of brain death. N. Engl. J. Med.344; 1215 - 21

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