It may be wrong to define death purely in medical terms, an academic argues.
Professor Allan Kellehear said the medical diagnosis of brain death was at odds with society's view of when death actually occurs.
He said a debate was needed about whether it was right to use brain death as the key criterion for switching off life support, and removing organs.
Professor Kellehear, of the University of Bath, will put this view at an international conference on Wednesday.
He argues that the current emphasis on brain death has come from a select cabal of doctors, and is at least in part driven by the need to harvest organs for transplant.
He said that although relatives were consulted about whether or not to switch off life support, many did not truly understand what they were agreeing to - or sign up to brain death as the definitive measure of end of life.
A diagnosis of brain death is made using factors such as fixed and dilated pupils, lack of eye movement and the absence of respiratory reflexes.
However, it is not based on whether or not the heart is still beating - for most people the most telling sign of death of all.
Professor Kellehear said this made the decisions potentially unsettling for the bereaved.
He said: "Forty years ago, being dead used to be very simple - it was the point at which your heart stopped beating.
"Now death itself has been complicated by the fact that we can keep alive people who are brain dead almost indefinitely.
"Brain death is the point at which doctors can switch off machines or begin harvesting organs, but, to relatives, being brain dead is not the same as being a corpse.
"Corpses are not warm, they are not pink, they do not move, they are not pregnant - but a person who is brain dead can be all of these things."
Professor Kellehear said there was little apparent difference to the untrained observer between a person who was brain dead, and somebody who was asleep.
Rare chance of recovery
He said the situation was further complicated by the fact that one in 1,000 people who are brain dead survive when life-support machines are switched off.
"If it is your daughter lying there, your idea of a remote chance is very different from that of your daughter's doctor.
"The situation at present is that these decisions are based on medical information alone.
"I would argue that these should be social decisions. To better inform these decisions, we need a closer look at the social implications of brain death."
Dr Richard Nicholson, editor of the Bulletin of Medical Ethics, said the current medical definition of death had partly arisen out of the need to ensure that organs harvested for transplant were still fit for purpose.
Medical technology in the 1960s and 1970s was such that if the heart had been allowed to stop beating the chance of retrieving usable organs was slim.
He said: "There has never been a really serious national debate about whether this is socially acceptable, or just medical pragmatism."
"I suspect it does create real problems for an awful lot of relatives when they are asked if organs can be removed when the patient's heart is still beating."
The Academy of Medical Royal Colleges is due to publish a report into how death is defined in the autumn. This will become the new code of practice for doctors.
Professor Kellehear will speak at the international conference on death, dying & disposal at the University of Bath.