How to define death ?

Defining death can be difficult because of differing concepts based on context; namely religious, cultural, legal or scientific. For Brain stem death ( BSD ) , the context is scientific. Defining death as the biological event that marks the transition from being alive to being dead is hard to argue against but is unhelpful because it does not provide criteria that describe what is meant by being alive or being dead. Death is the permanent cessation of the critical functions of the organism as whole'.

In the United Kingdom (UK), BSD is defined as irreversible loss of consciousness, irreversible loss of the capacity to breathe and irreversible loss of integrated functioning. The UK definition has merit because it permits criteria to be derived that are not only explicit but also testable. The inclusion of irreversible loss of integrated functioning implies death of the organism as a whole, not the whole organism. It is important to recognise that currently, whatever criteria and tests are chosen, we are only able to diagnose the state of being dead, not the event of death.

Worldwide, two distinct mechanisms of death are recognised; namely irreversible cardiopulmonary arrest and Brain stem death (BSD) or Brain death (BD). Scientifically, this distinction is artificial. Cardiopulmonary arrest only causes inevitable death if the brain stem is irreparably damaged due to lack of perfusion with oxygenated blood. Thus, the key feature of both mechanisms is irreparable brain damage. The two mechanisms differ only because death is diagnosed in the presence or absence of a beating heart.

Unfortunately, the general public normally associates death with cardiac standstill. This is an emotive issue and is most easily discussed in the context of heart-lung transplantation patients receiving extracorporeal membrane oxygenator support. These patients are alive despite the fact that the diseased heart and lungs have been removed. Their brains are capable of integrated function and the patient would be fully conscious were it not for the fact that anaesthesia is administered.

Many relatives find brain death easier to accept if it is explained that although the brain relies on the heart to circulate oxygenated blood, this function can be replicated by machines. In contrast brain function cannot be artificially replaced and the heart always stops within days or weeks of the brain stem dying.

By diagnosing BSD, we have not changed the nature of death. We have, however, improved our diagnostic skills and moved the time that we diagnose the state of being dead closer to the time when death actually occurred.