You’re still retrievable.”

Safar’s work began to change our perceptions of death – blurring the point that is meant to mark the end of our lives. “We’ve all been brought up to think death is an absolute moment – when you die you can’t come back,” says Sam Parnia, at the State University of New York in Stony Brook. “It used to be correct, but now with the basic discovery of CPR we’ve come to understand that the cells inside your body don’t become irreversibly ‘dead’ for hours after you’ve ‘died’… Even after you’ve become a cadaver, you’re still retrievable.”

Blurred line

Tisherman now thinks of death as the (admittedly subjective) point at which doctors give up resuscitation as a lost cause – but even then, some people can still make a remarkable comeback. Last December, a paper in the journal Resuscitation caused a stir by suggesting that 50% of surveyed emergency doctors have witnessed ‘Lazarus phenomena’, in which a patient’s heart has begun beating again by itself, after doctors had given up hope.

Kick-starting the heart is only one half of the doctor’s battle, however; the lack of oxygen after a cardiac arrest can cause serious damage to the body’s vital organs, particularly the brain. “Every minute that there’s no oxygen to those organs, they start dying,” says Tisherman. His former mentor, Safar, came up with a solution to this problem too, with ‘therapeutic hypothermia’, a procedure that involves cooling the body, typically to around 33C by placing ice packs around the body, for instance. At lower temperatures, cells begin to work in slow motion, reducing their metabolism and the damage that could be caused by oxygen starvation.