NEUROPHYSIOLOGIC BASIS OF
BRAIN DEATH
Areas of the Brain Involved
in Brain Death
By definition, brain death is a total irreversible cessation of
functioning of the brain. Brain includes all the
CNS structures except the spinal cord. However, the definition used by the International
Federation of Societies for Electroencephalography and Clinical Neurophysiology includes
the first cervical spine segment.[7]
It is generally
agreed that brain death does not include lower portions of the spinal cord (caudal
from C2), because their location outside the skull spares them from compression during
brain edema. Histologic studies of human spinal cord in cases of brain death revealed
divergent pathologic findings ranging from histologically intact tissues to complete
destruction.[19]
The United Kingdom[9]
[19]
and some other European countries[2]
supported a
rather exceptional criterion for brain death, one that excludes involvement of the
bilateral cerebral cortices.[20]
This state, known
as brainstem death, does not require recording of
an electroencephalogram (EEG) for its diagnosis. In the United Kingdom, no confirmatory
test (including an EEG) is required. Eleven (19.6%) of 56 clinically brainstem-dead
patients had electroencephalographic activity, and 2 patients (3.6%) even demonstrated
sleeplike cortical electroencephalographic activity for as long as 168 hours, although
none of the patients recovered.[21]
The rationale
for excluding the cerebral cortices is the fact that the brainstem, not the cerebral
cortices, plays the major role in controlling whole-body vital activities such as
respiration, circulation, and other homeostatic functions. We believe that if the
cerebral cortices were excluded, assessment of brainstem functions would be more
accurate, and the danger of mistaking the vegetative state for brain death could
be avoided.
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