Brain death: Difference between revisions
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Therefore, this is a circular definition, |
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[[ja:脳死]] |
[[ja:脳死]] |
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Today, where a definition of the moment of [[death]] is required, doctors usually turn to the concept of '''brain death''' which considers people to be dead when the [[EEG|electrical activity]] in their [[brain]] ceases permanently |
Today, where a definition of the moment of [[death]] is required, doctors usually turn to the concept of '''brain death''' which considers people to be dead when the [[EEG|electrical activity]] in their [[brain]] ceases permanently. The determination of the exact moment of death is important in determining when resuscitation efforts should end and when [[organ transplant]]s are allowed; this is highly controversial in some infant diseases such as [[anencephaly]], in which there is no higher brain present. |
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Once brain death occurs, it is not believed possible to return to life. Therefore, this is a circular definition, as brain death is defined to occur when EEG activity ceases ''permanently'', and the only way of being sure of that is to wait until the person dies of some other cause without regaining a normal EEG. In practice, a rule of thumb based on experience is used. |
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Note that brain electrical activity can stop completely, or apparently completely (a "flat [[electroencephalogram|EEG]]") for some time in deep [[anaesthesia]] or during [[cardiac arrest]] before being restored: brain death refers only to permanent cessation of electrical activity. Numerous people who have experienced such "flat line" experiences have reported [[near death experience]]s, the nature of which is controversial. |
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It is presumed that a permanent stoppage of electrical activity indicates the end of [[consciousness]]. Those that view that only the [[neo-cortex]] of the brain is necessary for consciousness, however, sometimes argue that only electrical activity there should be considered when defining death. In many cases, especially when elevated [[intracranial pressure]] prevents blood flow into the [[skull]], the entire brain is nonfunctional; however, some injuries may affect only the neo-cortex. |
It is presumed that a permanent stoppage of electrical activity indicates the end of [[consciousness]]. Those that view that only the [[neo-cortex]] of the brain is necessary for consciousness, however, sometimes argue that only electrical activity there should be considered when defining death. In many cases, especially when elevated [[intracranial pressure]] prevents blood flow into the [[skull]], the entire brain is nonfunctional; however, some injuries may affect only the neo-cortex. |
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In most places the more conservative definition of death (cessation of electrical activity in the whole brain, as opposed to just in the neo-cortex) has been adopted (for example the [[Uniform Definition of Death Act]] in the [[United States]]). Protocols for determining brain death generally require two EEGs showing no electrical activity, taken 24 hours apart. The absence of brain activity (including brain stem activity) necessarily implies that the patient is incapable of maintaining heartbeat or breathing unassisted by a respirator; and that cerebral reflexes are absent. |
In most places the more conservative definition of death (cessation of electrical activity in the whole brain, as opposed to just in the neo-cortex) has been adopted (for example the [[Uniform Definition of Death Act]] in the [[United States]]). Protocols for determining brain death generally require two EEGs showing no electrical activity, taken 24 hours apart. The absence of brain activity (including brain stem activity) necessarily implies that the patient is incapable of maintaining heartbeat or breathing unassisted by a respirator; and that cerebral reflexes are absent. |
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References: |
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* Karasawa H, ''et al'' Intracranial electroencephalographic changes in deep anesthesia. ''Clin Neurophysiol.'' 2001 Jan;112(1):25-30. |
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Revision as of 23:02, 16 March 2004
Today, where a definition of the moment of death is required, doctors usually turn to the concept of brain death which considers people to be dead when the electrical activity in their brain ceases permanently. The determination of the exact moment of death is important in determining when resuscitation efforts should end and when organ transplants are allowed; this is highly controversial in some infant diseases such as anencephaly, in which there is no higher brain present.
Once brain death occurs, it is not believed possible to return to life. Therefore, this is a circular definition, as brain death is defined to occur when EEG activity ceases permanently, and the only way of being sure of that is to wait until the person dies of some other cause without regaining a normal EEG. In practice, a rule of thumb based on experience is used.
Note that brain electrical activity can stop completely, or apparently completely (a "flat EEG") for some time in deep anaesthesia or during cardiac arrest before being restored: brain death refers only to permanent cessation of electrical activity. Numerous people who have experienced such "flat line" experiences have reported near death experiences, the nature of which is controversial.
It is presumed that a permanent stoppage of electrical activity indicates the end of consciousness. Those that view that only the neo-cortex of the brain is necessary for consciousness, however, sometimes argue that only electrical activity there should be considered when defining death. In many cases, especially when elevated intracranial pressure prevents blood flow into the skull, the entire brain is nonfunctional; however, some injuries may affect only the neo-cortex.
In most places the more conservative definition of death (cessation of electrical activity in the whole brain, as opposed to just in the neo-cortex) has been adopted (for example the Uniform Definition of Death Act in the United States). Protocols for determining brain death generally require two EEGs showing no electrical activity, taken 24 hours apart. The absence of brain activity (including brain stem activity) necessarily implies that the patient is incapable of maintaining heartbeat or breathing unassisted by a respirator; and that cerebral reflexes are absent.
References:
- Karasawa H, et al Intracranial electroencephalographic changes in deep anesthesia. Clin Neurophysiol. 2001 Jan;112(1):25-30.