The syndromes of permanent unconsciousness include two major types. The first is a permanent coma: an eyes-closed, sleeplike form of unarousable unconsciousness. The second is the permanent vegetative state: an eyes-open, wakeful form of unconsciousness (U.S. President's Commission for the Study of Ethical Problems). This entry takes no position on the ethical and legal issues involved in choosing between the whole-brain and higher-brain formulations of death but describes the neurological syndromes of permanent unconsciousness that would be considered the medical basis for the higher-brain formulation of death.
A permanent coma is an uncommon neurological syndrome because most patients with damage sufficient to cause brainstem impairment resulting in permanent coma die soon either naturally or because a decision is made to discontinue treatment as a result of the poor prognosis. Cases of prolonged (more than a few weeks) permanent coma do occur but are extremely uncommon.
The vegetative state has three major classes, depending on the temporal profile of the onset and the progression of the brain damage. The first form is the acute vegetative state. This occurs when the onset of brain damage is sudden and severe, such as with head trauma (traumatic vegetative state) or loss of blood flow to the brain caused by sudden cardiorespiratory insufficiencies (hypoxic-ischemic vegetative state). The second form is the degenerative, or metabolic, vegetative state, in which the brain damage begins gradually and progresses slowly over a period of months to years. In adults the most common form of the degenerative vegetative state is the final stage of Alzheimer's disease, whereas in children it is the final stage of a variety of degenerative and metabolic diseases of childhood. The third form is the congenital vegetative state secondary to a variety of severe congenital malformations of the brain that are present at birth, such as anencephaly.
The vegetative state is considered persistent when it is present longer than one month in the acute form and permanent when the condition becomes irreversible. The exact prevalence is unknown, but it is estimated that in the United States there are approximately 10,000 to 25,000 adults and 4,000 to 10,000 children in a vegetative state (Multi-Society Task Force on PVS). When it becomes permanent, this syndrome is the major neurological condition that is the prototype for the higher-brain formulation of death.
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