Every state recognizes brain death. But rules vary, and the true line separating life from death is ambiguous as ever. Resistance to the diagnosis of brain death is increasing, said Thaddeus Pope, a bioethicist and professor at the Mitchell Hamline School of Law in Minnesota who tracks brain death litigation. Over the past few years, highly publicized lawsuits have stirred skepticism among advocates and family members of those who have been declared brain dead. Some reject brain death on religious grounds, while others hold out hope that their loved one might somehow recover. Even among physicians, there is disagreement about exactly what constitutes brain death, and hospitals across the country have different protocols in place for making a diagnosis.

These conflicts threaten to undermine the entire concept of brain death and limit physicians’ authority to determine who is dead, said Ariane Lewis, a neurocritical care physician at New York University Langone Medical Center. She and others pushed for a formal review — now in its preliminary stages — of the Uniform Determination of Death Act, the standard for brain-death determination in the U.S. since the early 1980s. Lewis acknowledges the concept of brain death is not just a medical issue, but also a legal, religious, and societal one.

“That being said, for the sake of society, there does need to be common ground as to how death is defined,” she said.

The current standard defines brain death as “the irreversible cessation of all functions of the entire brain, including the brainstem,” which connects the brain to the spinal cord and plays a critical role in regulating heartbeat and sleeping. Brain death is different from a coma, where the loss of brain function is temporary. Brain death also differs from a persistent vegetative state, where a patient is permanently unconscious but able to breathe without assistance.

The public has trouble distinguishing between these diagnoses, in part because of misinformation from news media, television shows, and movies, says Lewis. For example, a character on a show might be described as being brain dead yet still on life support, implying they are still alive. “That is obviously confusing,” Lewis said. “Or there’s misleading information like the phrase ‘recovery from brain death.’”

Before the 1950s, such confusion did not exist because there was only one way to die: cardiopulmonary death, which occurs when the heart stops beating. The introduction of mechanical ventilators allowed patients to keep breathing even when the brain was too impaired to sustain it. That created, for the first time, the problem of what to do about patients who would never regain consciousness and were unable to breathe on their own. Should they remain in intensive care units, attached to ventilators until their hearts stop beating?