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What is brain death? Is it irreversible?

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Brain death is one of the most relevant medical phenomena, since it is a state that serves as a criterion to determine the point at which a person ceases to be resuscitated. Although there are exceptional cases, in general, brain death is what we popularly understand by "death", to dry.

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

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

However, today it is known that it is possible for cardiorespiratory functions to stop and still be able to stay 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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A person's brain death is considered to occur 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 They are capable of causing similar symptoms that may be recoverable or may only lead to a partial cessation of functions. Thus, for brain death to be diagnosed, it is necessary to certify that there is no possibility of recovery, and for this it is necessary to carry out verifiable tests and the application of very systematized.

Brain death is usually caused by massive brain damage, especially when the brainstem is injured (in charge of regulating aspects such as breathing and heartbeat). One of the most common causes of brain death occurs when intracranial pressure exceeds the systolic blood 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 reach the brain and therefore it stops working due to 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 non-existence of the different brain functions through various protocols. Specifically, it is stipulated that at least two different specialized doctors must perform the examination of 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 checking and more repetitions of these as your brain is more immature and it costs more to perform the scan neurological.

To diagnose brain death, it is essential to take into account whether the subject is in conditions that allow such verification. For this, the body must have cardiac respiratory stability, 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 more than 32º C.

Also it is necessary to rule out that the organism is in a state of intoxication due to drugs or under the influence of psychotropic drugs, since some substances can cause apparent death, and even many substances of the type psycholeptic or depressant can be misleading by preventing responses to different stimulations. 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 analyzed.

1. Irreversible and arreactive coma

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

2. Brain activity: flat encephalogram

Through the encephalogram brain bioelectric activity is measured. Thus, the fact 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. However, it must be borne in mind that to obtain these images you have 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 verified when establishing the brain death of a person is that they are not able to breathe on their own. For this, the apnea test is used, through which artificial respiration is temporarily stopped (having previously oxygenated the blood) to observe if the individual breathes on his own same 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 the paCO2 exceeds 60 mmHg (which indicates maximum stimulation of the respiratory centers), the test is considered to be positive in indicating absence of respiration, 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 the substance that gives the test its name into the bloodstream. In subjects with their own heart rate, this injection would mean an increase and acceleration of the heart rate, with which the absence of a reaction is a negative indicator. In this way, doing this serves to obtain an effective criterion to establish whether or not there is brain death.

5. Absence of brain stem-derived reflexes

When the brain dies, the different typical reflexes and reactions to different types of stimuli cease to occur. The brain stem is the area of ​​the brain that regulates the most basic aspects and functions of life, so that the reflexes that develop in this area are some of the most basic, so their absence suggests the existence of death cerebral.

One of the reflections to explore is the photomotor reflection, that is, whether or not the eye has a pupillary reaction to the light level (for example, focusing a flashlight directly on the pupil). In case of brain death there must be no type of reaction to light stimulation.

Another reflex 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. Cold liquids are also introduced into the ear, which in brain-alive 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 for any type 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 found. For example, an attempt is made to induce nausea by stimulating the palate and phalanx. The trachea is also stimulated in an attempt to elicit responses in the form of coughing or nausea. In any of the cases, if we are facing a case of brain death, there must 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 them all 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 this one is usually requires that the patient has entered an irreversible coma, the latter is not identified with death cerebral.

The patient in a coma, although he remains unconscious and is in many cases incapable of responding to stimuli, you still have a certain level of brain activity which means that you can still be considered alive even if you need life support to keep your heart pumping blood and artificial respiration. Although it is not always reversible in many cases there is that possibility. People who come out of 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 locked-in syndrome. In this strange syndrome the subject does not present any type of stimulating reaction, but is nevertheless fully aware of what is happening around him. In some cases they can move their eyes. It is usually caused by damage to the brainstem from brain injury, overdose, or vascular problems or accidents.

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Conflicting 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, some cases of people who have been considered brain dead and who have subsequently been resuscitated.

The explanation of this phenomenon seems simple: although it is possible, it is tremendously difficult to assert that a brain is unrecoverable, as occurs in some cases derived from hypothermia or substance use. 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 alteration of the tests performed due to not taking into account certain conditions of the subject (state of shock, hypothermia, consumption of medications or metabolic disturbances) or confusion with conditions similar to brain death but without Come to her.

It may be possible to find that the brain dies for a short period of time and the patient is able to recover if the reason for the cessation of the functioning is reversible and the brain is reactivated, but in principle brain death conceptually supposes that there is an irreversibility in that state. So, at least at present (although it does not seem likely, perhaps in the future, scientific research can discover ways to regain the functionality of a brain that is already dead if it is preserved) death cerebral 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 family members have given permission for said organs can be removed and transplanted, including those organs that have been artificially maintained, such as the heart.

In this regard, it must be taken into account that the donation of some of them is only possible if the organ is keeps functioning, having to be transplanted directly after death while the organ continues with lifetime. For this reason, it is a process developed with urgency, something that partly puts pressure when determining at what point a person is no longer "resuscitated".

The relative of the absence of life

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

Furthermore, it shows that the line that separates life from death is not as clear as one might think at one point, and that it is somewhat relative. If the right technical means were in place, it would be possible to revive practically anyone as long as the brain tissues did not deteriorate and that a way was found to reactivate several groups of neurons relevant to the time. Neither the absence of a heartbeat is the objective sign that someone has left, never to return, nor does it make sense that it should be.

Bibliographic references:

  • Davis, P.G.; Tan, A.; O'Donnell, C.P.F.; Schulze, A. (2004). Resuscitation of newborn infants with 100% oxygen or air: a systematic review and meta-analysis. The Lancet. 364 (9442): pp. 1329 - 1333.
  • Escudero, D. (2009). Diagnosis of brain death. Intensive Medicine vol.33, 4. Intensive Medicine Service. Central University Hospital of Asturias.
  • Purves, D., Augustine, G. J. & Fitzpatrick, D. (2004). Neuroscience. MA: Sinauer.
  • Racine, E.; Amaram, R.; Seidler, M.; Karczewska, M. & Illes, J. (2008). Media coverage of the persistent vegetative state and end-of-life and decision-making. Neurology, 23; 71 (13): 1027-32.
  • Richmond, T.S. (May 1997). Cerebral Resuscitation after Global Brain Ischemia, AACN Clinical Issues 8 (2).
  • Taylor, T; Dineen, R.A.; Gardiner, D.C.; Buss, C.H.; Howatson, A.; Pace, N.L. (2014). Computed tomography (CT) angiography for confirmation of the clinical diagnosis of brain death. The Cochrane Database of Systematic Reviews. 3 (3): CD009694.
  • Wijdicks, E.F.M. (2001). The diagnosis of brain death. N. Engl. J. Med. 344; 1215 - 21.
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