The only thing you can be certain about in life is death. Or is it? Merriam-Webster defines death as "a permanent cessation of all vital functions." The Oxford English dictionary refines that to "the permanent ending of vital processes in a cell or tissue." But determining when someone is dead is surprisingly complicated—the medical definition has changed over the centuries and, in many ways, is still evolving.
For most of human history, doctors relied on basic observations to determine whether or not a person had died. (This may be why so many feared being buried alive and went to great lengths to ensure they wouldn't be.) According to Marion Leary, the director of innovation research for the Center for Resuscitation Science at the University of Pennsylvania, "If a person wasn't visibly breathing, if they were cold and bluish in color, for example, they would be considered dead."
As time went on, the markers for death changed. Before the mid-1700s, for example, people were declared dead when their hearts stopped beating—a conclusion drawn from watching traumatic deaths such as decapitations, where the heart seemed to be the last organ to give up. But as our understanding of the human body grew, other organs, like the lungs and brain, were considered metrics of life—or death.
Today, that remains true to some degree; you can still be declared dead when your heart and lungs cease activity. And yet you can also be declared dead if both organs are still working, but your brain is not.
In most countries, being brain dead—meaning the whole brain has stopped working and cannot return to functionality—is the standard for calling death, says neuroscientist James Bernat, of the Geisel School of Medicine at Dartmouth College in New Hampshire. "A doctor has to show that the loss of brain function is irreversible," he tells Mental Floss. In some cases, a person can appear to be brain dead if they have overdosed on certain drugs or have suffered from hypothermia, for example, but the lack of activity is only temporary—these people aren't truly brain dead.
In the U.S., all states follow some form of the Uniform Determination of Death Act, which in 1981 defined a dead person as "an individual who has sustained either (1) irreversible cessation of circulatory and respiratory functions, or (2) irreversible cessation of all functions of the entire brain, including the brain stem."
But that's not the end of the story. In two states, New York and New Jersey, families can reject the concept of brain death if it goes against their religious beliefs. This makes it possible for someone to be considered alive in some states and dead in others.
A BLURRED LINE
In the past, if one of a person's three vital systems—circulation, respiration, and brain function—failed, the rest would usually stop within minutes of each other, and there was no coming back from that. But today, thanks to technological advances and medical breakthroughs, that's no longer necessarily the case. CPR can be performed to restart a heartbeat; a person who has suffered cardiac arrest can often be resuscitated within a 20- to 30-minute window (in rare cases, people have been revived after several hours). And since the 1950s, machines have been used to take on the role of many of the body's vital functions. People who stop breathing naturally can be hooked up to ventilators to move air in and out of their lungs, for example.
While remarkable, this life-extending technology has blurred the line between life and death. "A person can now have certain characteristics of being alive and others of being dead," Bernat says.
People with severe, irreversible brain damage fall into this mixed category. Many lie in intensive care units where ventilators breathe for them, but because they have minimal reflexes or movements, they're considered alive, especially by their families. Medical professionals, however, may disagree, leading to painful and complex debates about whether someone is alive.
Take the case of Jahi McMath, whose tonsil surgery in 2013, at age 13, went terribly wrong, leaving her brain dead—or so doctors thought. Her family refused to believe she was dead and moved her from Oakland, California, to New Jersey, where she was provided with feeding tubes in addition to her ventilator. After several months, her mother began recording videos that she said were proof that Jahi could move different parts of her body when asked to. Additional brain scans revealed that although some parts of her brain, like her brain stem, were largely destroyed, the structure of large parts of her cerebrum, which is responsible for consciousness, language, and voluntary movements, was intact. Her heart rate also changed when her mother spoke, leading a neurologist to declare last year, after viewing many of her mother's videos, that she is technically alive—nearly four years after she was pronounced brain dead. By her mother's reckoning, Jahi turned 17 on October 24, 2017.
Organ donation adds another layer of complications. Since an organ needs to be transplanted as quickly as possible to avoid damage, doctors want to declare death as soon as they can after a person has been disconnected from a machine. The protocol is usually to wait for five minutes after a donor's heart and breathing have stopped. However, some believe that's not long enough, since the person could still be resuscitated at that point.
Bernat—whose research interests include brain death and the definition of death, consciousness disorders including coma and vegetative states, and ethical and philosophical issues in neurology—disagrees. "I would argue that breathing and circulation has permanently ceased even if it hasn't irreversibly ceased," he says. "It won't restart by itself."
THE FUTURE OF BRINGING PEOPLE BACK TO LIFE
As resuscitation technology improves, scientists may find new ways to reverse death. One promising approach is therapeutic hypothermia. Sometimes used on heart attack patients who have been revived, the therapy uses cooling devices to lower body temperature, usually for about 24 hours. "It improves a patient's chance of recovering from cardiac arrest and the brain injury [from a lack of oxygen] that can result from it," says Leary, who specializes in research and education relating to cardiac arrest, CPR quality, and therapeutic hypothermia.
One more out-there possibility—which had its heyday in the early 2000s but still has its proponents today—is cryonic freezing, in which dead bodies (and in some cases, just people's heads) are preserved in the hope that they can be brought back once technology advances. Just minutes after death, a cryonaut's body is chilled; a chest compression device called a thumper keeps blood flowing through the body, which is then shot up with anticoagulants to prevent blood clots from forming; and finally, the blood is flushed out and replaced with a kind of antifreeze to halt the cell damage that usually occurs from freezing.
The idea is highly controversial. "It makes a good story for a movie, but it seems crazy to me," Bernat says. "I don't think it's the answer." But even if cryogenics is out, Bernat does believe that certain types of brain damage now thought to be permanent could one day be subject to medical intervention. "There is currently a huge effort in many medical centers to study brain resuscitation," he says.
Genetics provides another potential frontier. Scientists recently found that some genes in mice and fish live on after they die. And even more surprisingly, other genes regulating embryonic development, which switch off when an animal is born, turn on again after death. We don't yet know if the same thing happens in humans.