Biomedical Engineering Reference
In-Depth Information
Consider the case of the patient who sustains a serious head injury in an automobile
accident. To the attendants in the ambulance who reached the scene of the accident, the
patient was unconscious but still alive with a beating heart. After the victim was rushed to
the hospital and into the emergency room, the resident in charge verified the stability of
the vital signs of heartbeat and respiration during examination and ordered a computerized
tomography (CT) scan to indicate the extent of the head injury. The results of this procedure
clearly showed extensive brain damage. When the EEG was obtained from the scalp elec-
trodes placed about the head, it was noted to be significantly abnormal. In this situation, then,
the obvious questions arise: What is the status of the patient? Is the patient alive?
Alternatively, consider the events encountered during one open-heart surgery. During
this procedure, the patient was placed on the heart bypass machine while the surgeon
attempted to correct a malfunctioning valve. As the complex and long operation continued,
the EEG monitors that had indicated a normal pattern of electrical activity at the onset of
the operation suddenly displayed a relatively straight line indicative of feeble electrical
activity. However, since the heart-lung bypass was maintaining the patient's so-called vital
signs, what should the surgeon do? Should the medical staff continue on the basis that the
patient is alive, or is the patient dead?
The increasing occurrence of these situations has stimulated health professionals to reex-
amine the definition of “death.” In essence, advances in medical technology that delay
death actually hastened its redefinition. This should not be so surprising because the defi-
nition of death has always been closely related to the extent of medical knowledge
and available technology. For many centuries, death was defined solely as the absence of
breathing. Since it was felt that the spirit of the human being resided in the spiritus (breath),
its absence became indicative of death. With the continuing proliferation of scientific informa-
tion regarding human physiology and the development of techniques to revive a nonbreathing
person, attention turned to the pulsating heart as the focal point in determination of death.
However, this view was to change through additional medical and technological advances
in supportive therapy, resuscitation, cardiovascular assist devices, and organ transplantation.
As understanding of the human organism increased, it became obvious that one of the
primary constituents of the blood is oxygen and that any organ deprived of oxygen for a
specified period of time will cease to function and die. The higher functions of the brain
are particularly vulnerable to this type of insult, since the removal of oxygen from the blood
supply even for a short period of time (three minutes) produces irreversible damage to the
brain tissues. Consequently, the evidence of “death” began to shift from the pulsating heart
to the vital, functioning brain. Once medicine was provided with the means to monitor the
brain's activity (i.e., the EEG), another factor was introduced in the definition of death.
Advocates of the concept of brain death argued that the human brain is truly essential to
life. When the brain is irreversibly damaged, so are the functions that are identified with
self and our own humanness: memory, feeling, thinking, knowledge, and so on.
As a result, it became widely accepted that the meaning of clinical death implies that the
spontaneous activity of the lungs, heart, and brain is no longer present. The irreversible ces-
sation of functioning of all three major organs—the heart, lungs, and brain—was required
before anyone was pronounced dead. Although damage to any other organ system such
as the liver or kidney may ultimately cause the death of the individual through a fatal effect
on the essential functions of the heart, lungs, or brain, this aspect was not included in the
definition of clinical death.
