Brain stem death - AbsoluteAstronomy.com

Brain Stem Death is a clinical concept, implying an irreversibly unconscious patient, with irreversible apnea

Apnea

Apnea, apnoea, or apnœa is a term for suspension of external breathing. During apnea there is no movement of the muscles of respiration and the volume of the lungs initially remains unchanged...

and irreversible loss of brain stem

Brain stem

In vertebrate anatomy the brainstem is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves...

reflexes. The concept defines the core physiological basis for neurological diagnosis of death

Death

Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....

in the United Kingdom

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

and elsewhere. It was formally adopted in the UK code of practice published in 1979 by the Conference of Medical Royal Colleges

Medical Royal Colleges

There are a number of medical royal colleges in the United Kingdom and Ireland. Each is responsible for a different speciality within the medical field...

and their Facilities.

Background

The development of the concept of Brain Stem Death can be traced from the early work of Molllaret and Goulon on Coma Dépassé in 1959, through the ground-breaking 1968 publication in the Journal of the American Medical Association of what became known as the Harvard Criteria, a set of criteria developed by the ad hoc committee of the Harvard Medical School

Harvard Medical School

Harvard Medical School is the graduate medical school of Harvard University. It is located in the Longwood Medical Area of the Mission Hill neighborhood of Boston, Massachusetts....

which began the process of establishing a neurological basis for diagnosing death, and on to the work of Mohandas and Chou in 1971, two Minneapolis neurosurgeons whose stress on aetiological preconditions and on the central role of the brain stem in determining the relevant clinical features led to the Minnesota Criteria, the true antecedent of all modern neurological criteria for a diagnosis of death, including Brain Stem Death, the subject of this article.

All modern neurological criteria of death are primarily met through clinical tests of brain stem function. These tests all seek to ascertain that “ brainstem reflexes, motor responses,and respiratory drive are absent in a normothermic, nondrugged comatose patient with a known irreversible massive brain lesion and no contributing metabolic derangements” Although the clinical tests employed are broadly similar, there are considerable difference across nations as to requirements for confirmatory electroencephalographic measurements and the nature of the tests of respiratory function.

Evolution of diagnostic criteria

Brain stem death has been the criterion in use in the United Kingdom

United Kingdom

for declaring death on neurological grounds since 1979, the diagnostic criteria having been published by the Conference of Medical Royal Colleges

Medical Royal Colleges

There are a number of medical royal colleges in the United Kingdom and Ireland. Each is responsible for a different speciality within the medical field...

in 1976 with advice from a sub-committee of the Transplant Advisory Panel.

The criteria were drafted in response to a perceived need for guidance in the management of deeply coma

Coma

In medicine, a coma is a state of unconsciousness, lasting more than 6 hours in which a person cannot be awakened, fails to respond normally to painful stimuli, light or sound, lacks a normal sleep-wake cycle and does not initiate voluntary actions. A person in a state of coma is described as...

tose patients with severe brain damage

Brain damage

"Brain damage" or "brain injury" is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors...

who were being kept alive by mechanical ventilators but showing no signs of recovery. The Conference sought “to establish diagnostic criteria of such rigour that on their fulfilment the mechanical ventilator can be switched off, in the secure knowledge that there is no possible chance of recovery”. The published criteria – negative responses to bedside tests of some reflexes with pathways through the brain stem

Brain stem

and a specified challenge to the brain stem respiratory centre, with caveats about exclusion of endocrine influences, metabolic factors and drug effects

Drug

A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...

- were held to be “sufficient to distinguish between those patients who retain the functional capacity to have a chance of even partial recovery and those where no such possibility exists”. Recognition of that state required the withdrawal of fruitless further artificial support so that death might be allowed to occur, thus “sparing relatives from the further emotional trauma of sterile hope”.

In 1979, the Conference of Medical Royal Colleges

Medical Royal Colleges

There are a number of medical royal colleges in the United Kingdom and Ireland. Each is responsible for a different speciality within the medical field...

promulgated its conclusion that the identification of its defined syndrome “means that the patient is dead”. This certification of death

Death

enabled the procurement of organs for transplant from the beating heart cadaver

Beating heart cadaver

A beating heart cadaver is a human body that though dead in all medical and legal definitions is attached to a medical ventilator and retains cardio-pulmonary functions. This will keep the organs of the dead body, including the heart, functioning and alive for a few days...

.

Subsequent UK Department of Health Codes of Practice governing the procurement of organs for transplant have required the prior certification of death on essentially similar guidelines.

In 1995, a Working Group of the Medical Royal Colleges formally adopted the more scientifically rigorous term for the syndrome, "brain stem death", originally put forward in 1976 and championed by Pallis and Harley, notably in a set of 1982 articles in the BMJ

BMJ

BMJ is a partially open-access peer-reviewed medical journal. Originally called the British Medical Journal, the title was officially shortened to BMJ in 1988. The journal is published by the BMJ Group, a wholly owned subsidiary of the British Medical Association...

. Pallis,C. From Brain Death to Brain Stem Death, BMJ, 285, November 1982 In doing so, it advanced a new definition of human death, viz. “irreversible loss of the capacity for consciousness, combined with irreversible loss of the capacity to breathe”, which it described as a “clinical state produced by the irreversible cessation of brain stem function (brain stem death)". Most countries in the Americas, Asia, Australasia and Europe had adopted similar criteria for a neurological diagnosis of death, although corresponding legal definitions of death itself vary, if they exist at all.

The UK brain stem death standard for the diagnosis of death on neurological grounds does not require testing for the persistence of electrical activity in other parts of the brain, an approach supported, on neurological grounds, by prominent neurologists in the United States and elsewhere, although not endorsed by a US Presidential Commission on the subject (see below). In France, Italy and Iran, amongst other countries, such confirmatory tests for the irreversible cessation of cellular activity in the entire brain, specifically including the brain stem, are mandatory. In the United States, Germany, United Kingdom, Poland, Canada, Australia and New Zealand, amongst others, they are not.

Diagnosis

The formal rules for the diagnosis of brain stem death – then called brain death – were first published in 1976. With only minor modifications, they have remained the basis on which death is diagnosed when a beating heart cadaver

Beating heart cadaver

is identified in the UK. The most recent revision of the Code of Practice governing that procedure reaffirms the preconditions for its consideration. These are:

There should be no doubt that the patient’s condition - deeply comatose, unresponsive and requiring artificial ventilation - is due to irreversible brain damage of known aetiology.
There should be no evidence that this state is due to depressant drugs.
Primary hypothermia as the cause of unconsciousness must have been excluded, and
Potentially reversible circulatory, metabolic and endocrine disturbances likewise.
Potentially reversible causes of apnoea (dependence on the ventilator), such as muscle relaxants and cervical cord injury, must be excluded.

With these pre-conditions satisfied, the definitive criteria are:

Fixed pupils which do not respond to sharp changes in the intensity of incident light.
No corneal reflex
Corneal reflex
The corneal reflex, also known as the blink reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea , or bright light, though could result from any peripheral stimulus. Stimulation should elicit both a direct and consensual response...

.
Absent oculo-vestibular reflexes – no eye movements following the slow injection of at least 50ml of ice-cold water into each ear in turn (the caloric test).
No response to supraorbital pressure.
No cough reflex to bronchial stimulation or gagging response to pharyngeal stimulation.
No observed respiratory effort in response to disconnection of the ventilator for long enough (typically 5 minutes) to ensure elevation of the arterial partial pressure of carbon dioxide to at least 6.0 kPa (6.5 kPa in patients with chronic carbon dioxide retention). Adequate oxygenation is ensured by pre-oxygenation and diffusion oxygenation during the disconnection (so the brain stem respiratory centre is not challenged by the ultimate, anoxic, drive stimulus). It should be noted this is a dangerous - potentially lethal – test.

Two doctors, of specified status and experience, are required to act together to diagnose death on these criteria and the tests must be repeated after “a short period of time … to allow return of the patient’s arterial blood gases and baseline parameters to the pre-test state”.
These criteria for the diagnosis of death are not applicable to infants below the age of two months.

Prognosis and management

With due regard for the cause of the coma, and the rapidity of its onset, testing for the purpose of diagnosing death on brain stem death grounds should be delayed beyond the stage where brain stem reflexes may be absent only temporarily – because the cerebral blood flow is inadequate to support synaptic function although there is still sufficient blood flow to keep brain cells alive and capable of recovery. There has recently been renewed interest in the possibility of neuronal protection during this phase by use of moderate hypothermia, and by correction of the neuroendocrine abnormalities commonly seen in this early stage.

Published studies of patients meeting the criteria for brain stem death or whole brain death – the American standard which includes brain stem death diagnosed by similar means – record that even if ventilation is continued after diagnosis, the heart stops beating within only a few hours or days . However, there have been some very long-term survivals and it is noteworthy that expert management can maintain the bodily functions of pregnant ‘brain dead’ women for long enough to bring them to term.

The official UK prognosis is that, if support is continued after diagnosis, “both adults and children will ultimately suffer cessation of heartbeat … often within a few days, but (it) may take weeks or even months if aggressive support is maintained, although there are no verified reports of patients recovering brain-stem function during this time”.

The management of patients pronounced dead on meeting the brain stem death criteria depends upon the reason for diagnosing death on that basis. If the body is to be used to harvest organs, the ventilator is reconnected and life-support measures are continued, perhaps intensified, with the addition of procedures designed to protect the wanted organs until they can be removed. If the priority is to ensure as little distress to the deceased's relatives as may still be possible, the ventilator is left disconnected on confirmation of the lack of respiratory centre response (the last test). In the second case, the diagnostic procedure may be less rigorous, e.g. omission of the caloric test which could be intensely, and unnecessarily, distressing to the relatives.

Criticism

The US President's Council on Bioethics, a body the majority of whose members were not medically qualified, and which included only one neurologist, described the UK standard as "conceptually suspect" and "clinically dangerous" in 2008 .

The diagnostic criteria were originally published for the purpose of identifying a clinical state associated with a fatal prognosis (see above). The change of use to criteria for the diagnosis of death itself was protested from the first. The initial basis for the change of use was the claim that satisfaction of the criteria sufficed for the diagnosis of the death of the brain as a whole, despite the persistence of demonstrable activity in parts of the brain. That claim was superseded in 1995; since then the diagnosis of death by the specified testing of brain stem functions was based on a new definition of death, viz. the permanent loss of the capacity for consciousness and spontaneous breathing. A small minority of UK practitioners have expressed doubts that this concept is generally understood and accepted or that the specified testing is stringent enough to determine that state.

It has been argued that sound scientific support is lacking for the claim that the specified purely bedside tests have the power to diagnose true and total death of the brain stem, the necessary condition for the assumption of permanent loss of the intrinsically untestable consciousness-arousal function of those elements of the reticular formation which lie within the brain stem (there are elements also within the higher brain). Knowledge of this arousal system is based upon the findings from animal experiments as illuminated by pathological studies in man.
The current neurological consensus, while fully supporting the use of the specified clinical tests as the basis for diagnosing loss of brain stem function, is that the arousal of consciousness depends upon reticular components which reside in the midbrain, diencephalon and pons. It is said that the midbrain reticular formation may be viewed as a driving centre for the higher structures, loss of which produces a state in which the cortex appears (on the basis of electroencephalographic studies) to be awaiting the command or ability to function. The rôle of diencephalic (higher brain) involvement is stated to be uncertain and we are reminded that the arousal system is best regarded as a physiological rather than a precise anatomical entity. There should, perhaps, also be a caveat about possible arousal mechanisms involving the first and second cranial nerves (serving sight and smell) which are not tested when diagnosing brain stem death but which were described in cats in 1935 and 1938.
There is also concern about the permanence of consciousness loss, based on studies in cats, dogs and monkeys which recovered consciousness days or weeks after being rendered comatose by brain stem ablation and on human studies of brain stem stroke raising thoughts about the “plasticity” of the nervous system.
Other theories of consciousness place more stress on the thalamocortical system. Perhaps the most objective statement to be made is that consciousness is not currently understood. That being so, proper caution must be exercised in accepting a diagnosis of its permanent loss before all cerebral blood flow has permanently ceased.

The ability to breathe

Breathe (Reprise)

"Breathe " is a song on Pink Floyd's album The Dark Side of the Moon. Following the song "Time", to which it serves as a coda, it reprises the earlier song "Breathe", with different lyrics...

spontaneously depends upon functioning elements in the medulla

Medulla

Medulla refers to the middle of something and derives from the Latin word for marrow. Its anatomical uses include:* Medulla oblongata, a part of the brain stem* Renal medulla, a part of the kidney* Adrenal medulla, a part of the adrenal gland...

– the ‘respiratory centre’. In the UK, establishing a neurological diagnosis of death involves challenging this centre with the strong stimulus offered by an unusually high concentration of carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

in the arterial blood, but it is not challenged by the more powerful drive stimulus provided by anoxia

Hypoxia (medical)

Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...

– although the effect of that ultimate stimulus is sometimes seen after final disconnection of the ventilator in the form of agonal gasps. Respiratory tests in other countries vary widely, and it seems to be the case that they are often performed improperly.

No testing of testable brain stem functions such as oesophageal and cardiovascular regulation is specified. There is published evidence strongly suggestive of the persistence of brain stem blood pressure control in organ donors.

A very small minority of medical practitioners working in the UK have argued that there is no scientific basis for equating the state known as brain stem death, as diagnosed by the UK Code, or any state diagnosed solely by the mandatory tests in the United States, Germany, Poland, Australia and elsewhere, with the death of the person. They have argued that neither requirement of the UK Health Department's Code of Practice basis for the equation of brain stem death with death is satisfied by its current diagnostic protocol, and that in terms of its ability to diagnose de facto brain stem death it falls far short. Such criticisms have rarely been accepted as articles in peer-reviewed medical journals.

Background

Evolution of diagnostic criteria

Diagnosis

Prognosis and management

Criticism

See also