Brain death is one of the most relevant medical phenomena , given that it is a state that serves as a criterion for determining the point at which a person ceases to be resuscitable. Although there are exceptional cases, in general, brain death is what we popularly understand by “death”, pure and simple.

In this article we will see what the characteristics that define this medical condition are.

What is brain death?

When we think of 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 expiration to refer to death or expressions such as exhaling the last breath are a clear reference to this way of seeing death.

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

Brain death is considered to occur when there is a complete and irreversible cessation of all brain functions , both in the hemispheres and in the brain stem. It is important to take into account the nuances of complete and irreversible, since different types of brain lesions are capable of causing similar symptoms that may be recoverable or only partially cease to function. Thus, in order to diagnose brain death, it is necessary to certify that there is no possibility of recovery, and this requires the performance of verifying tests and the application of highly systematized protocols.

Brain death is usually caused by massive injuries to the brain, especially when the brain stem (responsible for regulating aspects such as breathing and heartbeat) is injured. One of the most common causes of brain death is when the intracranial pressure exceeds the systolic blood pressure, culminating 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 the brain stops working because of hypoxia.

Diagnosis: key aspects to check

Diagnosing brain death is not easy , and for this it is necessary to prove the non-existence of the different brain functions through various protocols. Specifically, it is stipulated that at least two different specialised doctors must examine the patient, performing at least two physical examinations and two electroencephalograms separated in time.

In the cases of children under one year of age, the observation period is usually longer, requiring a higher level of testing and more repetition of tests as their brains are more immature and it costs more to perform the neurological exploration.

To diagnose brain death, it is essential to consider whether the subject is in a condition that allows such verification. To do so, the organism must have a stable cardiac respiration, either naturally or through artificial mechanisms, an adequate level of oxygenation in the blood and a temperature level that reflects the absence of hypothermia (which can itself cause symptoms similar to brain death). In this last aspect the body has to be at least above 32º C.

Also it is necessary to rule out that the organism is in a state of intoxication due to drugs or under the effects of psychopharmaceuticals, since some substances can cause apparent death, and even many substances of a psycholeptic or depressive type can be misleading by preventing responses to different stimuli. States due to metabolic problems, such as insulin coma, should also be ruled out.

Once these aspects have been taken into account prior to the neurological analysis, the following aspects can be analysed.

1. Irreversible and Reactive Coma State

To be able to diagnose brain death, the subject must be in a coma due to a known and well-established cause (ruling out aspects such as those 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 type of reaction to the stimulation. To verify this, the application of painful stimuli such as trigeminal nerve activation is used, and neither vegetative nor motor reactions should occur.

2. Brain activity: flat encephalogram

The encephalogram measures the bioelectric activity of the brain . In this way, the fact that it appears flat indicates that no brain activity is recorded, evidencing that the central nervous system has stopped acting.

In addition to the EEG, many other neuroimaging techniques can be used to test brain activity, such as evoked potentials or various types of CT scans. However, it must be taken into account that to obtain these images it is necessary to decide which algorithms to use, and depending on this the result will be different.

3. Breathing functions dependent on artificial elements

One of the aspects that are checked when establishing a person’s brain death is that he or she is not able to breathe on their own. To do this, the apnea test is used, through which artificial respiration is temporarily ceased (having previously oxygenated the blood) to observe whether the individual is breathing on his own 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 breathing movements are observed and paCO2 exceeds 60 mmHg (indicating maximum stimulation of the respiratory centers), the test is considered to be positive for absence of breathing, by reconnecting the subject to artificial respiration.

4. Absence of own heart functions

To check that the heart does not work on its own without mechanical assistance, the atropine test is applied by injecting the substance that gives the test its name into the bloodstream. In subjects with their own heart rate, this injection would increase and accelerate the heart rate, so that the absence of a reaction is a negative indicator. In this way, doing this serves to obtain an effective criterion for establishing whether or not there is brain death.

5. Absence of brain stem reflexes

When the brain dies, the different reflexes and reactions typical of different types of stimuli no longer occur. 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 are some of the most basic, so their absence suggests brain death.

One of the reflexes to be explored is the photomotor reflex , that is, whether or not the eye has a pupillary reaction at the level of light (for example, by focusing a flashlight directly on the pupil). In the case of brain death, there should be no reaction to light stimulation.

Another reflex to be taken into account is the corneal reflex, in which it is observed if there is a reaction to pain and rubbing by means of tactile stimulation through the use of gauze. Cold liquids are also introduced into the ear, which in subjects with a brain that is alive would cause a reaction in the form of eye movement (oculovestibular reflex). The oculocephalic reflex is also checked , by quickly turning the patient’s head horizontally to check if any eye movement occurs

Apart from the reflexes of the oculomotor system, the existence of reflexes linked to the nerves that govern the mouth and the digestive tract is also checked. For example, an attempt is made to provoke nausea by stimulating the palate and phalanx. The trachea is also stimulated in an attempt to provoke responses in the form of coughing or nausea. In either case, if we are dealing with a case of brain death there should be no reaction at all.

The confusion between brain death and other concepts

Brain death is a concept that may be easy to understand at first, but is often confused with other terms. The most common of these is the concept of coma.

While a coma may end up leading to the subject’s brain death and in fact the diagnosis of brain death usually requires that the patient has entered an irreversible coma, the latter is not identified with brain death.

The comatose patient, although remaining unconscious and in many cases unable to respond to stimuli, still has a certain level of brain activity that means he can still be considered alive even if life support is needed to keep his heart pumping blood and breathing. Although it is not always reversible in many cases there is that possibility. People who come out of such a state usually do so within the first two to four weeks, but in some cases the coma can last up to several decades.

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

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Contradictory cases: coming back from the dead

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

The explanation for this phenomenon seems simple: although it is possible, it is tremendously complicated to assert that a brain is unrecoverable, as occurs in some cases derived from hypothermia or substance abuse. Thus, some people who were not yet brain dead may have been misdiagnosed.

Some of the possible causes of this misdiagnosis may be due to the alteration of the tests performed due to not taking into account certain conditions of the subject (state of shock, hypothermia, consumption of medication or metabolic disorders) or confusion with conditions similar to but not reaching brain death.

It may be possible to find that the brain dies for a short period of time and that the patient recovers if the reason for the cessation of functioning is reversible and the brain is reactivated, but in principle brain death conceptually implies that there is an irreversibility in that state. Therefore, at least at present (although it seems unlikely that scientific research will be able to discover ways of recovering the functionality of an already dead brain if it is preserved), brain death means the end of life as such .

Organ donation

Once the patient’s brain death is diagnosed, artificial life support can be disconnected . However, if the patient has wanted to donate the organs or his or her family members have given permission for this, these organs may be removed and transplanted, including those organs that have been kept artificially, such as the heart.

In this aspect it must be taken into account that the donation of some of them is only possible if the organ is kept working, having to be transplanted directly after the death while the organ is still alive. Therefore, it is a process developed with urgency, something that in part involves pressure when determining at what point a person is no longer “resuscitable”.

The relative of the absence of life

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

It also shows that the line between life and death is not as clear as one might think at one time, and that it is a relative one. If the right technical means were available, it would be possible to revive virtually anyone as long as the brain tissues did not deteriorate and a way was found to reactivate several relevant groups of neurons at once. Neither is the absence of a heartbeat the objective sign that someone has left to avoid returning, nor does it make sense to do so.

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