Brain death is one of the most relevant medical phenomenasince it is a state that serves as a criterion to determine the point at which a person is no longer resuscitatable. Although there are exceptional cases, in general, brain death is what we popularly understand by “death”, simply.
In this article we will see what are the characteristics that define this medical state.
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 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’re talking about brain death.
A person’s brain death is considered to occur when complete and irreversible cessation of all brain functionsboth by 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 only involve 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 this requires the performance of confirmatory tests and the application of highly systematized protocols.
Brain death is usually caused by massive lesions of the brain, especially when the brain stem is injured (responsible for regulating aspects such as breathing and heartbeat). One of the most frequent causes of brain death occurs when intracranial pressure exceeds 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 reach the brain and therefore it stops functioning due to hypoxia.
Diagnosis: key aspects to check
Diagnosing brain death is not easyand for this it is necessary to prove the nonexistence of the different brain functions through various protocols. Specifically, it is stipulated that at least two different specialized 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 verification and more repetitions of these as their brain is more immature and it costs more to perform the neurological examination.
To diagnose brain death, it is essential to take into account whether the subject is in conditions that allow such verification. To do this, the body must have respiratory cardiac stability, either naturally or through artificial mechanisms, and an adequate level of blood oxygenation. and a temperature level that reflects the absence of hypothermia (which can itself cause brain death-like symptoms). In this last aspect, the body must be at least more than 32º C.
Also it is necessary to rule out that the body 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 psycholeptic or depressant-type substances can mislead by preventing responses from occurring to different stimulations. Conditions due to metabolic problems, such as insulin coma, must also be ruled out.
Once these aspects have been taken into account prior to the neurological analysis, we can proceed to analyze the following aspects.
1. Irreversible and unreactive 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 the 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. In this way, 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 taken into account that to obtain these images you must 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 a person’s brain death is that they are not able to breathe on their own. For this, the apnea test is usedthrough which artificial respiration is temporarily stopped (having previously oxygenated the blood) to observe if the individual breathes on his or her 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 respiratory movements are observed and the paCO2 exceeds 60 mmHg (which indicates maximum stimulation of the respiratory centers), the test is considered to give a positive result indicating the absence of breathing, reconnecting the subject to breathing. artificial.
4. Absence of cardiac functions
To check that the heart does not work on its own The atropine test is applied without mechanical assistance, injecting the substance that gives its name to the test into the bloodstream. In subjects with their own heart rate, such injection would lead to an increase and acceleration of the heart rate, so the absence of 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.
When the brain dies, the different reflexes and typical reactions to different types of stimuli stop occurring. 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 its absence suggests the existence of brain death.
One of the reflexes to explore is the photomotor reflex.that is, whether or not the eye presents a pupillary reaction to the light level (for example, focusing a flashlight directly on the pupil). In case of brain death there should 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 using gauze. Cold liquids are also introduced into the ear, which in cerebrally 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 if there is 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 digestive tract is also verified. For example, an attempt is made to provoke nausea by stimulating the palate and phalanx. The trachea is also stimulated in order to try to provoke responses in the form of coughing or nausea. In any case, if we are dealing with a case of brain death there should be no 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 all of them is the concept of a coma.
Although a coma can end up leading to brain death of the subject and in fact for the diagnosis of this 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 he remains unconscious and is in many cases unable to respond to stimuli, still have a certain level of brain activity which means that he can continue to be considered alive even if life support is required to keep his 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 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 locked-in syndrome.. In this strange syndrome the subject does not present any type of stimulus 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 brain stem resulting from injuries to it, overdose, or vascular problems or accidents.
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 cases of people who have been considered brain dead and who 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 derived from hypothermia or substance consumption. Thus, some people who were not yet brain dead may have been incorrectly diagnosed.
Some of the possible causes of said 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, medication consumption or metabolic alterations) 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 the patient recovers if the reason for the cessation of functioning is reversible and the brain can be reactivated, but in principle brain death conceptually implies that there is an irreversibility in that state. So at least currently (although it does not seem likely that perhaps in the future scientific research will be able to discover ways to recover 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 her family has given permission to do so, said organs can be extracted and transplanted, including those organs that have been maintained artificially, 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 remains functional, and must be transplanted directly after death while the organ is still alive. For this reason, it is a process developed with urgency, something that in part involves pressure when determining at what point a person stops being “resuscitable.”
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 is found in brain activity.
Furthermore, it shows that the line between life and death is not as clear as one might think at one time, and that it is something relative. If the appropriate technical means were available, it would be possible to revive practically anyone as long as the brain tissues did not deteriorate and a way was found to reactivate several relevant groups of neurons at the same time. Neither the absence of a heartbeat is the objective sign that someone has left and will not return, nor does it make sense for it to be so.
