[1] The premise of this is that a person is dead when consciousness and the ability to breathe are permanently lost, regardless of continuing life in the body and parts of the brain, and that death of the brainstem alone is sufficient to produce this state.
[5] The United Kingdom (UK) criteria were first published by the Conference of Medical Royal Colleges (with advice from the Transplant Advisory Panel) in 1976, as prognostic guidelines.
[6] They were drafted in response to a perceived need for guidance in the management of deeply comatose patients with severe brain damage 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".
Recognition of that state required the withdrawal of further artificial support so that death is allowed to occur, thus "sparing relatives from the further emotional trauma of sterile hope".
[6] In 1979, the Conference of Medical Royal Colleges promulgated its conclusion that identification of the state defined by those same criteria – then thought sufficient for a diagnosis of brain death – "means that the patient is dead".
[14] However, there have been some very long-term survivals[15] 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.
[24][25] 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 role 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 brainstem death but which were described in cats in 1935 and 1938.