The definition of death as “irreversible coma” was introduced in 1968 by the Harvard University Medical School. It was developed largely in diagnostic terms as the “irreversible cessation of all functions of the entire brain, including the brainstem.” In its review of brain death in 1981, The President’s Commission for the Study of Ethical Problems in Medicine argued that brain death is consonant with circulatory death because the loss of certain brain functions results in the “loss of integrative unity of (...) the organism,” leading to cardiac arrest. This picture of a unified conception of death was challenged by subsequent clinical evidence suggesting that, with proper treatment, circulatory death is not the inevitable result of brain death. Here, it is argued that, if death, in the morally relevant sense, is defined as irreversible loss of consciousness, a unitary conception of death can be maintained. However, significant theoretical and methodological obstacles remain in diagnosing irreversible loss of consciousness. (shrink)