Brain death: clinical criteria

Clinical criteria for brain death

Diagnosis of brain death at first glance is not very difficult: it is necessary to show that the brain has stopped functioning and its recovery is impossible. However, the extraordinary importance of such a diagnosis necessitates absolute accuracy in the final determination of this condition, therefore most diagnostic studies are devoted to the diagnosis of brain death. Conventionally, there are 2 types of diagnostic criteria - clinical signs and interpretation of these paraclinical methods. They are closely interrelated, they can only be considered together. Clinical criteria are generally recognized and practically the same throughout the world. The basis of their study was laid by the authors who first described the death of the brain. At that time, the signs were called neurological criteria for the death of a person:

• resistant bilateral mydriasis;
• complete absence of reaction to any stimuli (areactivity);
• absence of spontaneous breathing when disconnected from the ventilator for 5 minutes;
• mandatory use of vasopressors to maintain blood pressure;
• absence of bioelectric activity of the brain for several hours.

Further investigations that would improve the accuracy of diagnosis were mainly related to observations of cases of pathological conditions simulating brain death and aimed at their exclusion. In 1995, the US published the latest standards for diagnosing brain death. They are only advisory in nature, and the actions of doctors depend on state laws.

Thus, to establish a diagnosis of brain death, the presence of the following clinical signs is currently required.

• The reason for the development of this state must be known.
• Intoxications, including medications, primary hypothermia, hypovolemic shock, metabolic endocrine coma, and the use of narcotics and muscle relaxants should be avoided.
• During the clinical examination of the patient, rectal temperature should be stable above 32 ° C, systolic blood pressure not lower than 90 mm Hg. (at a lower pressure it should be increased by intravenous injection of vasopressor drugs). With intoxication, established as a result of toxicological research, the diagnosis of brain death before the disappearance of its symptoms is not considered.
• The following complex of clinical signs should be present:
  • complete and persistent absence of consciousness (coma);
  • atony of all muscles;
  • absence of reaction to severe painful stimulation in the region of trigeminal points and any other reflexes closing above the cervical spinal cord;
  • no pupillary reaction to direct bright light. In this case, it should be known that no drugs that dilate the pupils were used. The eyeballs are fixed;
  • absence of corneal reflexes;
  • absence of oculocephalic reflexes. These reflexes are not examined in the presence of traumatic injury of the cervical spine or suspected of it;
  • absence of oculo- vestibular reflexes. To study these reflexes, a two-sided calorie test is carried out. Before it is carried out, it must be ensured that there is no perforation of the eardrums;
  • absence of pharyngeal and tracheal reflexes, determined by the movement of the endotracheal tube in the trachea and upper respiratory tract, and also with the advancement of the catheter in the bronchi for aspiration of the secret;
  • lack of independent breathing.

The last point should be considered in more detail. It is unacceptable to register absence of breath by simple disconnection from the ventilator, since the developing hypoxia has a harmful effect on the body, especially on the brain and heart, therefore, an apneetic osigination test is used. It is carried out after the results of the clinical examination are obtained.

• For monitoring of blood gas (P _a O ₂ and P _a CO ₂ ) should be one of the cannulated artery limb.
• Before the fan is disconnected, it is necessary to carry out mechanical ventilation for 10-15 minutes in the regime providing normocapnia (р _а СО ₂ = 35-45 mm Hg) and hyperoxia (р _а О ₂ > 200 mm Hg); FiO ₂ - 1.0 (ie 100% oxygen), adequately selected minute ventilation of the lungs, optimal positive end-expiratory pressure.
• After this, the ventilator is switched off, and moisturized 100% oxygen is supplied to the endotracheal or tracheostomy tube at a rate of 6 l / min. The stages of control of the gas composition of the blood are as follows:
  • before the test in conditions of mechanical ventilation;
  • 10-15 minutes after the onset of mechanical ventilation, 100% oxygen;
  • immediately after being disconnected from the ventilator, then every 10 minutes until p _and CO ₂ reaches 60 mmHg
• If these or higher values of p _and CO ₂, the spontaneous respiratory movements are not restored, apnoeticheskoy oxygenation test indicates that the respiratory center of the brain stem is not functioning. With the appearance of minimal respiratory movements, ventilation is immediately resumed.

The attitude towards the test for apnea remains ambiguous. As is known, the apneetic oxygenation test is performed after the fact of loss of brain functions is established. There were no cases of survival or transition to the vegetative state of the patient with established complete loss of brain functions, but the appearing of respiratory movements during the apneic oxygenation test. Thus, the outcome of the condition is already predetermined and there is no need to expose the patient who is in a terminal state to a severe procedure. In addition, it is known that the apneetic oxygenation test can provoke the development of arterial hypotension and hypoxemia. In this regard, damage to organs suitable for transplantation is possible. Finally, it is believed that an apneetic oxygenation test can cause the death of potentially viable neurons. According to several authors, complications of the test develop in more than 60% of cases (acute arterial hypotension - 12%, acidosis - 68%, hypoxemia - 23%, etc.). On the other hand, the apnea test is the only clinical way to check the functioning of the medulla oblongata, and with proper observance of all the resuscitation measures preceding the test, it is completely safe.

Thus, the unambiguous opinion about the necessity and safety of the apneetic oxygenation test has not been developed by the medical community to date. Most researchers are inclined to perform an apneic oxygenation test after a neurologic examination, at the end of the observation period, and a set of paraclinical techniques confirming the diagnosis of "brain death". In the US and many countries of Western Europe, it has been established by law that with the development of complications during the apneic oxygenation test, it can be replaced by one of the diagnostic tests confirming the diagnosis of "brain death".

Difficulties in establishing the diagnosis of "brain death" can sometimes be associated with an incorrect interpretation of the presence and form of spinal automatisms. Especially dramatically, they are perceived by middle and junior medical staff working in intensive care units. It is shown that the presence of not only tendon reflexes, but also complex motor automatisms does not exclude the diagnosis of "brain death". The prevalence of this phenomenon is 25-39%, and the most dramatic is the so-called sign of Lazarus sign (bending of the body at 40-60 °, simulating rising).

Spinal automatisms and reflexes in patients with brain death

Part of the body	Occurring symptoms
Cervical spine	Tonic neck reflexes: spastic contracture of the neck muscles, flexion in the hip joint in response to the turn of the head, flexion in the elbow in response to the turn of the head, lowering of the shoulder in response to the turn of the head, spontaneous turning of the head to the side
Upper limbs	Unilateral extension is pronation. Isolated twitching of fingers. Flexion and lifting of the shoulder, the case with the connection of hands is described
Torso	Asymmetric opisthotonic position of the body. Flexion of the trunk in the lower back, simulating the sitting position. Abdominal reflexes
Lower limbs	Fold fingers in response to tapping. The phenomenon of triple flexion. Symptom Babinsky

Some authors believe that the phenomenon of triple flexion can be regarded as a complex undifferentiated response to stimulation. Such a reaction may be a symptom of an ongoing terminal wedging of the brain stem, excluding the diagnosis of "brain death".

Clinical conditions imitating brain death

At present, conditions are described, the clinical picture of which can imitate brain death. These include severe hypothermia (heart temperature below 28 ° C), acute poisoning, including drug poisoning, as well as acute metabolic encephalopathies associated with impaired functioning of an organ. Of greatest interest are drug intoxication. Differential diagnosis with them is constantly carried out in a clinical setting of the diagnosis of "brain death."

Drugs, the use of which can make it difficult to diagnose brain death

A drug	Half-life, h	Latitude of therapeutic action
Amitriptyline	10-24	75-200 ng / ml
Valproic acid	15-20	40-100 mmol / ml
Diazepam	40	0.2-0.8 mmol / ml
Carbamazepine	10-60	2-10 mmol / ml
Ketamine	2-4	No data
Clonazepam	20-30	10-50 ng / ml
Codeine	3	200-350 ng / ml
Cocaine	1	150-300 ng / ml
Lorazepam	10-20	0.1-0.3 mmol / ml
Midazolam	2-5	50-150 ng / ml
Morphine	2-3	70-450 mmol / ml
Alcohol	10*	800-1500 mg / l
Thiopental sodium	10	6-35 mmol / ml
Phenobarbital	100	10-20 mmol / ml
Fentanyl	18-60	No data

* Specified extraction speed in milliliters per hour.

[1], [2], [3], [4], [5], [6], [7],