What is brain death and is it irreversible?

What is the difference between this state and coma? Can a brain dead person be resuscitated?

Brain death is one of the most relevant medical phenomena, since it is a state that serves as a criterion for determining the point at which brain death can occur.It is a state that serves as a criterion for determining the point at which a person is no longer resuscitatable. Although there are exceptional cases, in general, brain death is what we popularly understand as "death", plain and simple.

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

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 expiring to refer to death or expressions such as exhaling the last breath are a clear reference to this way of looking at death.

However, nowadays it is known that it is possible for cardiorespiratory functions to stop and still be able to remain 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 of a person is considered to occur when there is a complete and irreversible cessation of brain activity. complete and irreversible cessation of all brain functions, both on the part of the hemispheres of the brain.It is important to take into account the nuances of brain death. It is important to bear in mind the nuances of complete and irreversible, since different types of brain lesions are capable of causing similar symptoms that may be recoverable or may involve only a partial cessation of functions. Thus, in order for brain death to be diagnosed, 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 brain injuries, especially when the brainstem is injured (responsible for regulating (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 arterial pressure, which culminates in the cessation of Blood circulation in the brain. In this state the blood generally loaded with oxygen and nutrients does not arrive at the brain and therefore this one stops working because of the hypoxia.

Diagnosis: key aspects to check

Diagnosing brain death is not easyIt is necessary to prove the non-existence of the different brain functions through various protocols. Specifically, it is stipulated that at least two different specialized physicians must examine the patient, 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, as their brains are more immature and the neurological examination is more difficult to perform.

In order to diagnose brain death, it is essential to consider whether the subject is in a condition that allows such verification. For this, the organism must have respiratory cardiac stability, either naturally or through artificial mechanisms, an adequate blood oxygenation level, and a temperature level that reflects the absence of hypothermia. and a temperature level that reflects the absence of hypothermia (which can itself cause brain death-like symptoms). (which can itself cause brain death-like symptoms). In the latter respect the body must be at least above 32º C.

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

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

1. Irreversible and arreactive coma state.

In order to diagnose brain death, the subject must be in a coma due to a known cause. must be in coma due to a known and well-established cause (discarding and well established (ruling out aspects such as hypothermia or intoxication, for example). One of the main aspects to be verified is that the subject in question has no reaction to stimulation. To verify this, the application of painful stimuli such as trigeminal nerve activation is used, and neither vegetative nor motor reactions should be produced.

2. Brain activity: flat encephalogram

Through the encephalogram the brain bioelectrical activity is measured. Thus, if it appears flat, this indicates that there is no brain activity, indicating that the central nervous system has ceased to act.

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. However, it should be borne in mind that in order to obtain these images it is necessary to decide which algorithms to use, and depending on this the result will be different.

3. Respiratory functions dependent on artificial elements

One of the aspects that are checked when establishing the brain death of a person is that he or she is not able to breathe on his or her own. For this purpose, the apnea test is used.This test, through which artificial respiration is temporarily ceased (having previously oxygenated the blood) to observe whether the individual is breathing on his/her own by observing respiratory movements and measuring the partial pressure of carbon dioxide in the blood of the arteries (paCO2).

If no respiratory movements are observed and paCO2 exceeds 60 mmHg (indicating maximal stimulation of the respiratory centers), the test is considered positive in indicating the absence of respiration and the subject is reconnected to artificial respiration.

4. Absence of proper cardiac functions

To verify that the heart does not function on its own without mechanical 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, such an injection would result in an increase and acceleration of the heart rate, so that the absence of reaction is a negative indicator. Thus, doing this serves to obtain an effective criterion to establish whether or not there is brain death.

5. Absence of brainstem-derived reflexes

When the brain dies, the different reflexes and typical reactions to different types of stimuli are no longer present. The brainstem is the area of the brain that regulates the most basic aspects and functions for life, so that the reflexes that develop in this area are some of the most basic, so that their absence suggests the existence of brain death.

One of the reflexes to be explored is the photomotor reflexthat is to say, whether or not the eye presents a pupillary reaction to 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 whether there is a reaction to pain and friction by means of tactile stimulation with the use of gauze. Cold liquids are also introduced into the ear, which in brain-living subjects would provoke a reaction in the form of eye movement (oculovestibular reflex). The oculocephalic reflex is also tested.The oculocephalic reflex is also checked by rapidly turning the patient's head horizontally to check for any kind of eye movement.

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 the phalange. The trachea is also stimulated in order to try to provoke responses in the form of coughing or nausea. In any of the cases, if we are in front of a case of brain death there must not be any type of reaction.

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 these is the concept of coma.

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

The comatose patient, while remaining unconscious and in many cases unable to respond to stimuli, still has a certain level of brain activity, still has a certain level of brain activity which means that he can still be considered alive even if life support is needed to keep his heart pumping blood and artificial respiration. Although it is not always reversible, in many cases it is possible. People who emerge from 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 locked-in syndrome.. In this strange syndrome the subject does not present any type of stimulating reaction, but nevertheless is 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 brainstem derived from lesions in it, overdose or vascular problems or accidents.

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 after 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. people who have been considered brain dead and have subsequently been resuscitated..

The explanation for this phenomenon seems simple: although it is possible, it is extremely difficult to assert that a brain is irrecoverable, as occurs in some cases resulting from hypothermia or substance abuse. Thus, some people who were not yet brain dead may have been incorrectly diagnosed.

Some of the possible causes of such misdiagnosis may be due to the alteration of the tests performed due to failure to take into account certain conditions of the subject (shock, hypothermia, consumption of drugs or metabolic disturbances) or confusion with conditions similar to brain death but not leading to it.

It may be possible to find that the brain dies for a short period of time and that the patient manages to recover if the reason for the cessation of functioning is reversible and the brain is reactivated, but in principle brain death conceptually assumes that there is an irreversibility in that state. Thus, at least at present (although it seems unlikely that in the future scientific research may discover 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 patient is diagnosed as brain dead, disconnection of artificial life support can be performed.. However, if the patient has wanted to donate organs or his or her relatives have given permission to do so, these organs can be removed and transplanted, including those organs that have been artificially maintained, 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 still functioning, having to be transplanted directly after death while the organ is still alive. Therefore, it is a process developed with urgency, which in part puts pressure on determining at what point a person ceases to be "resuscitatable".

The relative nature of lifelessness

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

It also shows that the line between life and death is not as clear-cut as one might think at first, and that it is relative. If the right technical means were available, it would be possible to revive virtually anyone, provided the brain tissues did not deteriorate and a way could be found to reactivate several groups of relevant neurons at the same time. Neither is the absence of a heartbeat the objective sign that someone is gone never to return, nor does it make sense that it should be.

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