The philosophical underpinnings of the equating of brain death to death, giving it the same status as cessation of cardiorespiratory death, are more complex. In particular, the ethical and moral dimensions of brain death are subject to differing interpretations in various societies, religions, and cultures. Some of these are reviewed in a perspective article by the prominent writers Magnus, Wilford, and Caplan, who suggest that the wide medical and societal acceptance of brain death makes it an important construct, not to be abandoned because of philosophical objections. One justification for equating brain death with somatic death is the general inevitability of cardiorespiratory failure in patients who fulfill the standard criteria. This tenet has exceptions, among the most striking of which is a well-studied case of 20-year survival in a boy who had meningitis reported by Reptinger and colleagues, and other cases of long that have been described with varying degrees of documentation. These have been collected by Shewmon who makes the point that arguments equating brain death with death on the basis of the brain’s role in creating “somatic unity” are weakened by the existence of such long surviving cases as well as by delivery of live babies from brain-dead mothers. Further clouding the issue of validity of brain death is the proposal by British and Scandinavian neurologists that death of the brainstem alone is adequate to fulfill the precepts of brain death. In the end, these philosophical concerns truly matter but the operational state called brain death at the moment serves both patients and society well and is compatible with most of the world’s religions.
The central considerations in the diagnosis of brain death are (1) absence of all cerebral functions; (2) absence of all brainstem functions, including spontaneous respiration; and (3) irreversibility of the state. Following from the last of these criteria, it is necessary to demonstrate an irrefutable cause of the underlying catastrophic brain damage (e.g., trauma, cardiac arrest, cerebral hemorrhage) and to exclude reversible causes such as drug overdose and extreme hypothermia.
In the diagnosis of brain death, the absence of cerebral function is demonstrated by the presence of deep coma and total lack of spontaneous movement and of motor and vocal responses to all visual, auditory, and cutaneous stimulation. Spinal reflexes (deep tendons reflexes) may persist, and the toes often flex slowly in response to plantar stimulation; but a well-developed Babinski sign is unusual (although its presence does not exclude brain death). Extensor or flexor posturing is seen from time to time as a transitional phenomenon just before or after brain death becomes evident, and the status of these movements in the diagnosis is ambiguous, but most criteria consider these movements to be incompatible with brain death, as they reflect functioning of brainstem centers. The physician should therefore proceed cautiously in declaring a patient dead in the presence of posturing and should consider conducting the examination again at a later time.
The complete absence of brainstem function is judged by the loss of spontaneous eye movements, the resting position of both globes at the meridian of the palpebral fissures, and lack of response to oculocephalic and caloric (vestibulo-ocular) testing; the presence of dilated or midposition fixed pupils (not smaller than 3 mm); paralysis of bulbar musculature (no facial movement or gag, cough, corneal, or sucking reflexes); absence of motor and autonomic responses to noxious stimuli; and absence of respiratory movements. The clinical findings should show complete absence of brain function, not an approximation that might be reflected, for example, by small or poorly reactive pupils, slight eye deviation with oculovestibular stimulation, or posturing of the limbs, as mentioned earlier.