The concept of brain death presupposes the viability of the body in the absence of brain and brainstem function. Until the invention of effective positive pressure mechanical ventilation by Bjorn Ibsen in the mid-twentieth century, brain death – as distinguished from mere coma – was not conceivable in broad understanding. Circulatory arrest had long been the sole criterion of death, but medical scientists at the turn of the twentieth century, such as Horsley [1], Duckworth [2], and Cushing [3], observed in cases of severe neurological injury the cessation of respiration prior to circulatory arrest. Apnea in some of these cases was reversible if the brain was decompressed or the offending injury removed. The idea began to form that the brain could die prior to cardiac arrest, but until the advent of mechanical ventilation, death remained defined as the moment the heart permanently stopped functioning [4].