Similarities:
Both have the death of nerve cells in the brain
Loss of consciousness
Both require extensive medical care
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Differences:
Brain death is usually defined as the irreversible loss of function of the entire brain, including the brainstem. Due to the loss of brainstem function, the person's most basic functions/reflexes are also lost, and the main clinical manifestations are
Active respiratory arrest
Irreversible deep coma. No voluntary muscle activity, but spinal reflexes can still be present
Disappearance of brainstem neurological reflexes (cranial reflexes)
Dilated or fixed pupils, unresponsive to light intensity
Disappearance of brain waves in the form of a flat, straight line
Cerebral blood circulation completely stops
There are a variety of criteria for determining brain death, with the most universal being the Harvard criteria [2]. There are only four criteria:
①No receptivity and responsiveness to external stimuli and internal needs, i.e., the patient is in an irreversible deep coma, with a complete loss of all receptivity to external stimuli and internal needs, as well as a complete loss of the resultant responsiveness;
2) Loss of voluntary muscular movements and voluntary respiration;
3) Loss of induced reflexes;
④) Flat EEG brain waves, and a flat EEG brain wave. EEG showed flat brain waves.
The above four criteria should be observed continuously for 24 hours, and the patient can be declared dead (brain dead) if the results of repeated tests are unchanged and the cases of hypothermia (<32.2℃) or the cases of central nervous system depressants such as barbiturates have just been taken are excluded.
The most important thing that distinguishes the persistent vegetative state (PVS) from brain death is that the brainstem is still functioning, so the person in PVS has a heartbeat and usually has reflexes (brainstem function.) The person in PVS may awaken or may remain in a coma until his or her condition worsens. Some PVS patients even have detectable cortical activity that can be visualized using devices such as EEG, fMRI, PET, etc. [3-5].
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A slightly better state than the PVS state is the Minimally Conscious State (MCS ), which is when the patient has deliberate movements (reaching toward objects, responding to commands or the environment) rather than reflexes. Another state is called Locked-in syndrome (LCS), in which the patient is conscious but is unable to move or speak on his or her own due to the paralysis of all the random muscles of the body (except the eyes). PET imaging features of normal consciousness, vegetative state, locked-in syndrome, and minimal conscious state