In 1986, a two-and-a-half year-old girl named Michelle Funk fell into a stream and drowned. By the time paramedics found her, she hadn’t been breathing for more than an hour. Her heart was stopped. In other words, she was dead. Somewhat inexplicably, the paramedics continued to work on her, and so did doctors in the emergency room. Then, three hours after she died, Michelle Funk took a breath and her heart fluttered back into action.

Funk’s case inspired David Casarett to go to medical school, with plans to become an ER doctor. He wanted to bring people back to life. Casarett is now an associate professor of medicine at the University of Pennsylvania. In his new book, Shocked: Adventures in Bringing Back the Recently Dead, he explores the history, science, and moral hazards of reviving the recently dead.

Casarett is enthusiastic about the emerging technologies that are allowing doctors to save patients who would have been a lost cause in the very recent past. But these technologies come at a cost, he writes. They may restore life, but whether it’s a life worth living is another matter.

As inspired as he was by Funk’s near-miraculous revival, Casarett has also seen heartbreaking cases in which patients were revived with heroic efforts—only to languish, unresponsive, in an ICU for weeks while their families agonize over how long to maintain life support. Those cases caused Casarett to abandon his plans to become an ER doc. He now focuses on easing the suffering of patients near the end of life as a palliative care and hospice doctor.

Here are a few things he’d like you to know about reviving the dead.

Be glad you weren’t recently deceased in the 18th century ———————————————————

In the 1700s, Good Samaritans in several European cities began to take a keen interest in reviving people who appeared to have drowned. Their methods seem dubious today: throwing the no-longer breathing person onto a trotting horse or dunking them in freezing water, tickling the back of the throat with a feather, blowing tobacco smoke into the rectum, or administering a good whipping.

But not all these methods are totally without scientific grounding, Casarett writes. The up and down motion of a trotting horse could move the diaphragm and chest walls in and out enough to force air in and out of the lungs and stimulate some circulation, not unlike CPR. And tobacco smoke contains nicotine, which prompts the brain to release epinephrine, which in turn increases the rate and strength of the heart’s contractions. In fact, epinephrine is a key item in modern day crash carts.

“Some of the techniques they tried back then were bizarre, but some of them actually turned out to be direct ancestors of things we use today,” Casarett said. “Mouth-to mouth resuscitation was pioneered, as far as I can tell, in Amsterdam in the late 18th century, and it’s still a mainstay of resuscitation today.”

If you want to die and live to tell about it, go somewhere cold —————————————————————

Casarett recounts several remarkable tales of people who defied the odds by coming back to life after an hour or more without breathing and without a pulse. A young Swedish woman, for example, survived 80 minutes trapped under the ice in a frozen stream. In all these cases, the person was somewhere cold.

That’s not a coincidence. When cells are deprived of oxygen and nutrients, they soon begin to self-destruct. Cold delays this process by reducing cells’ metabolic needs. That allows the brain and other organs to escape damage for far longer than they would have otherwise. “If this happened at room temperature, there’s virtually no chance they would have survived, at least not cognitively intact,” Casarett said.

“Today, some of the most exciting work in resuscitation medicine involves making people cold,” he said.

Otherwise, try Pittsburgh ————————-

Indeed, a clinical trial underway at the University of Pittsburgh Medical Center will put this idea to the test in trauma patients. Only in dire cases where massive blood loss has caused cardiac arrest, doctors will replace the patient’s blood with ice-cold saline solution in hopes of buying time to repair the wounds before cells and organs begin to break down. There’s been some ethical discussion about the trial because the patients will be unconscious and therefore unable to give informed consent (people can request a bracelet that would let doctors know they wish to opt out).

Casarett says he’s not familiar enough with the details of the trial to comment on the ethical issues, but he’s fascinated by the science behind it. In Shocked, he describes some of the experiments with dogs and pigs that laid the foundation for the trial. “This isn’t just a half-baked idea, it has a pretty strong basis in molecular biology,” he said.

“If you’re going to get in an accident anywhere in the U.S. in the next few years, I would try to have it happen in Pittsburgh,” Casarett said. “You’d have a chance of getting what may become the standard of care in the next five or ten years.”

The squirrels have secrets ————————–

Hibernation is the way animals like bears and squirrels ramp down their metabolism to survive winter. If humans could be put in a similar state of suspended animation, it might be an alternative to putting them on ice (or replacing their blood with freezing saline) to preserve the brain and other organs.

For all its advantages, cooling patients has its disadvantages too: It makes it harder to restore a normal heart rhythm and it requires a lot of equipment, making it difficult to use outside a hospital. A chemical that could do the same thing might be more effective and more widely useful, Casarett says.

In researching Shocked, he visited the labs of scientists trying to understand the biochemical changes that occur when animals like squirrels, mice, and lemurs (the only known hibernating primates) enter a hypometabolic state. It’s still early days, but Casarett says it’s not too crazy to imagine a future in which crash carts and ambulances carry a drug derived from a compound found in hibernating animals. “Imagine a drug that could do everything that buckets of ice could do, but could do it much more quickly in a single injection,” he said. “That would be the goal.”

Don’t waste your money on cryonics ———————————-

The most lively chapter in Shocked recounts Casarett’s visit to a cryonics convention, where he meets people willing to pony up $200,000 to put their bodies on ice after they die, in hopes that scientists will eventually come up with a cure for whatever killed them.

“I had expected to be in a room full of freaks and geeks, and certainly some people were completely nuts, but I was surprised by the degree to which some people were really very knowledgeable,” he said.

He was impressed by scientific talks on how to cool a recently deceased body as quickly as possible and how to freeze it without the formation of ice crystals, which can tear tissue apart and throw electrolyte concentrations out of whack.

All in all, however, he left unconvinced that cryonauts will be successfully frozen and reanimated anytime soon. “I can think of a lot of other ways to spend that money,” he said.

Kiss the dummy and shock strangers ———————————-

Blowing into someone’s mouth and pumping on their chest during CPR helps get a little bit of oxygen into their blood and circulate it until an ambulance arrives. It saves lives, and Casarett wants everyone to take a course and practice on Annie, the ubiquitous CPR training dummy.

Even people who don’t know CPR can save the life of someone in cardiac arrest with an automated electronic defibrillator (AED). These devices can detect an abnormal heart rhythm and issue voice commands to guide even a novice user to apply an electric shock to correct it. Together, more people trained in CPR and more AEDs in public places, constitute a strategy for what Casarett calls crowdsourced survival.

We’re not there yet, though. A colleague of his at Penn has found that AEDs are more common in rich areas of Philadelphia than in lower income neighborhoods. And California’s Supreme Court recently ruled that big box retailers like Target aren’t obligated to have an AED in their stores.

Resuscitation doesn’t work like you see on TV ———————————————

The biggest difference between resuscitation as shown on TV medical dramas and reality is the likelihood of success, Casarett says. “On TV they make it look much easier and more effective than it is in real life.” He notes that one study in the 1990s actually tried to quantify this: the researchers found that 75 percent of people who received CPR in several TV medical dramas survived, compared to less than 30 percent in real life.

Another difference: Recently revived people often throw up. That’s because when you’re unconscious, your muscles relax, including the sphincter muscle at the bottom of your esophagus that normally keeps your stomach contents from coming back up. Relax that muscle in someone lying on their back while another person is pounding on their chest, and… it’s easy to understand why the recently revived often have some spitting up to do. “That’s something you usually don’t see on television,” Casarett said.

Dying isn’t as simple as it used to be ————————————–

The line between alive and dead is getting blurrier thanks to advances in technology, Casarett writes. “Several emergency room physicians I talked to told me that even five years ago, when confronted with a cardiac arrest patient, you would run through the routine, do what you could, and then it would be pretty clear at some point that you’d exhausted your bag of tricks and there was nothing else you could do,” Casarett said. But now there are more and more things to try.

For example, extracorporeal membrane oxygenation machines can withdraw the blood of a patient in heart failure, oxygenate it, and pump it back into the body, keeping them alive—or something like it. “That line is getting more difficult to define because of all these technologies,” Casarett said.

Coming back from the dead comes at a cost —————————————–

Restoring life may be getting easier, but the quality of that life can be questionable, especially when a revived patient never regains consciousness. “It’s not a chance to say goodbye or even grieve, it just draws out the dying process,” Casarett said. And then there’s the issue no one likes to talk about, the financial costs, which can run to more than $20,000 a day.

As medical science marches forward, we can expect more incredible stories of revival, Casarett writes. But we also have to expect more hard decisions about the emotional and financial costs of these new technologies, and what kind of life—and death—they’ll provide.