Brain stem death

For patient information click here

Overview
Brain Stem Death is the specific formulation of the concept of brain death formally adopted in the UK in 1995.

Diagnosis
The diagnostic features of brain stem death are a deep coma, dependence for oxygenation on a mechanical ventilator, and the absence of specified reflexes which depend upon circuits within the brain stem. Formal rules for its diagnosis were first published in 1976, by the UK Conference of Medical Royal Colleges, acting with advice from the Transplant Advisory Panel. They specified tests for the pupillary light reflex, the corneal reflex, vestibulo-ocular reflex, motor reflexes with brain stem arcs, the gag reflex and reflex response to bronchial stimulation. Reversible causes of coma (such as drugs, hypothermia, metabolic and endocrine abnormalities) had to be excluded. Ventilator dependence was confirmed by disconnection for long enough to ensure that the medullary respiratory centre was exposed to a powerful hypercapnic drive stimulus (PaCO2 ≥ 6.65kPa). Its exposure to the ultimate anoxic drive stimulus was avoided by pre-oxygenation and continuing oxygenation by diffusion. No testing of the medullary centres controlling heart-rate and blood pressure was required. The prescribed tests were required to be repeated, at an unspecified interval, "to ensure that there has been no observer error".

With only minor modifications, these rules for the diagnosis of the syndrome have become the basis for Codes of Practice governing the procurement of organs for transplantation which have been published by the United Kingdom Department of Health between 1980 and 1998. They are currently under further review.

Prognosis and Management
Except when diagnosed too early - when the absence of demonstrable synaptic function cannot be equated with irrecoverability - final circulatory arrest occurs within a few days in almost all cases. However, there have been exceptional long-term survivals and, most significantly, some pregnant women have been kept alive to become mothers several weeks after they were, or could have been, diagnosed "brain stem dead". (reference needed) Brain stem death as diagnosed by the UK Code of Practice rules may therefore be seen as a very late stage of the dying process, although not as late as that described - as "le coma dėpassė" - by Mollaret and Goulon in 1959, whose syndrome included circulatory collapse.

Identification of this syndrome was held, by the Conference of the Medical Royal Colleges in 1976, to require withdrawal of "further artificial support" - particularly fruitless mechanical ventilation of a cadaver - thus "sparing relatives from the further emotional trauma of sterile hope". The diagnostic criteria being accepted by this authoritative body as "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", no legal problems with this withdrawal of life-support measures, in the sole interests of the patient and his relatives, were likely to be encountered.

Controversial aspects
Perhaps influenced by the ad hoc Harvard Committee report of 1968 and the later Minnesota study, death of the brain stem, as diagnosed by purely bedside tests, was identified with brain death by Conference in their 1976 publication. In a Memorandum published in 1979, the same criteria were declared sufficient for the diagnosis of death itself, despite the presence of a normally regulated circulation and continuing(artificially supported) respiration. No scientific or philosophical basis for this change of use of the essentially prognostic criteria was given.

In 1995, Conference abandoned the looser term 'brain death', in favour of the "more correct" term 'brain stem death' thenceforth. However, it was not made clear that use of the term should not be seen as implying the diagnosis of death of the whole of the brain stem (however defined anatomically) in the de facto pathological sense - there being no requirement to test the medullary cardiovascular or oesophageal motility centres or to challenge the respiratory centre to the ultimate anoxic drive stimulus (even the specified apnoea testing being potentially lethal). The brain stem formulation of brain death is based on the fact that the reticular formation is essential for consciousness. This is important because Conference continued to underwrite the diagnosis and certification of death on the basis of their essentially prognostic criteria, claiming that satisfaction thereof meant that there could never again be any possibility of spontaneous breathing or of consciousness in any form. Whatever one may think of that particular concept of human death, a minority view within the profession holds that without subjecting the respiratory centre to the most extreme determination of persistent apnoea, one cannot be certain of the irreversible loss of the capacity to breathe spontaneously. Others, on essentially religious grounds, object that the generation of consciousness is not sufficiently understood to invoke it in this context. Finally, even if a quintessential role for brain stem arousal mechanisms is accepted, some objectors feel that they are not directly testable and can only be considered permanently functionless if the whole of the brain stem is shown to be destroyed.

A Working Group was set up by the UK Academy of Medical Royal Colleges in 2004 to revisit the guidelines ensuring that the criteria for diagnosing brain stem death are properly met, partly in light of anomalies in the way the tests are carried out in practice. To date (February 2008) the Working Group has not issued its formal report.

For a discussion of the general concept of a neurological rather than a cardiac definition of death, see the article on brain death.