Brain Stem Death - Criticism

Criticism

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, in the UK, 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. In 1995, that claim was abandoned and the diagnosis of death (acceptable for legal purposes in the UK in the context of organ procurement for transplantation) 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. There are 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 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 (EEG) 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. In man, light flashes have been observed to disturb the sleep-like EEG activity persisting after the loss of all brain stem reflexes and of spontaneous respiration.

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 spontaneously depends upon functioning elements in the medulla – 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 in the arterial blood, but it is not challenged by the more powerful drive stimulus provided by anoxia – although the effect of that ultimate stimulus is sometimes seen after final disconnection of the ventilator in the form of agonal gasps.

No testing of testable brain stem functions such as oesophageal and cardiovascular regulation is specified in the UK Code of Practice for the diagnosis of death on neurological grounds. There is published evidence strongly suggestive of the persistence of brain stem blood pressure control in organ donors.

A small minority of medical practitioners working in the UK 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.