Within moments of his on-field cardiac arrest on Monday, Buffalo Bills safety Damar Hamlin was receiving CPR and medical personnel were called in to restart his heart. That rapid response is credited with dramatically improving his chance of survival and recovery.

The University of Cincinnati Medical Center, where Hamlin had been listed in critical condition, reported Thursday a "substantial improvement" in his condition.

"As of this morning, he is beginning to awaken and it appears his neurological condition and function is intact," said Dr. Timothy Pritts of UCMC during a videoconference for the media. "This marks a really good turning point in his ongoing care."

For the more than 350,000 Americans each year who suffer cardiac arrest outside of a hospital, the prognosis is not always an optimistic one. Most studies suggest that no more than 10% of these patients survive until hospital discharge.

As grim as that would seem, medical experts say the statistics mask much better individual outcomes for patients who receive rapid and appropriate care before they reach a hospital.

For many, trained bystanders are key to survival

Jeff Feig, 56, a private investor, was relaxing at a summer community in 2016 in Westchester, N.Y., when he suddenly found himself out of breath.

"It was like a switch. I felt terribly sick. I remember thinking, I've just got to sit down," he says.

Feig knows the rest of the story only from bystanders, some of whom quickly intervened and are credited with helping to save his life. "My heart stopped. My eyes rolled to the back of my head. I was foaming at the mouth," he says.

Feig's out-of-hospital cardiac arrest, also known as OHCA, occurred under circumstances that undoubtedly increased his chances for survival. Only a week before, the bystanders who helped him had received CPR training and instruction on use of the community's automated external defibrillator, or AED, a device that allows minimally trained individuals to administer a potentially lifesaving shock to a stopped heart. Many AEDs are now programmed with verbal commands to talk a user through the process.

A 2018 survey by the Cleveland Clinic found that slightly more than half of Americans (54%) reported that they knew how to perform CPR, but only about 11% knew the correct pacing for performing chest compressions (100 to 12o beats per minute). A recent survey published in the Journal of the American Heart Association found that just 18% of people are up to date on their CPR training.

In what's known as the "chain of survival," quick recognition of sudden cardiac distress, early CPR and early defibrillation are key, says Dr. Myron Weisfeldt, a professor of medicine at Johns Hopkins University.

Most out-of-hospital cardiac arrests occur in the home

Some 70% of out-of-hospital cardiac arrests (OHCA) occur in the home, another 18.8% in public settings and 11.2% in nursing homes, according to the American Heart Association. In many cases, family, friends and bystanders are unsure how to respond, says Weisfeldt, who has authored or co-authored several papers on OHCA.

That uncertainty wastes precious time and rapidly reduces the odds of survival, he says.

Data suggests that for every minute that defibrillation is delayed, the chances of survival decrease by 10%, according to Weisfeldt.

However, with CPR and defibrillation on the scene of an OHCA, odds of making it increase significantly, he says.

CPR is best thought of as an "effective bridge" to defibrillation, according to Weisfeldt. "Rapid defibrillation is really important to survival and to survival with good brain function," he says.

AEDs have become common in many high-traffic buildings and in nursing homes, and various state laws require their placement in schools, health and fitness centers, public golf courses and gambling establishments.

In homes, such devices are rare, says Dr. Douglas Kupas, an EMS physician and medical director for the National Association of Emergency Medical Technicians.

And even in public places, the location of an AED might not be obvious. In those cases, it's important for one person to start chest compressions immediately. If another person is available, they should be the one to look for the AED, he says.

"That makes a whole lot more sense than ... the only person who knows CPR running around the building trying to find an AED," says Kupas, who is also director of resuscitation programs for Geisinger Health System in central Pennsylvania.

Being healthy increases odds

Being healthy "significantly increases" the chances of survival from an OHCA, says Dr. Stephen Anderson, an emergency medicine physician who recently retired after 35 years of practice in Seattle.

To illustrate how a rapid response can make a big difference for patients like these, Anderson points to the example of a casino that was just 8 miles from where he worked.

"If you fall down to the ground in a casino, they respond immediately" with CPR and defibrillation from an AED, says Anderson, who is spokesman for the American College of Emergency Physicians.

"I have taken care of countless people ... who have cardiac arrest at the casino and come [into the hospital] talking and awake," he says.

What can you do?

Physicians say that if more people got CPR-trained, including in the use of the AED, more lives could be saved. Keeping that training up to date is also important.

"Any type of reinforcement of the skill is very, very helpful," Kupas says. "But I think we have to get over the idea that you have to be fully trained, you have to be certified, you have to have a card that's not expired or else you're not any good at this."

"If you took [CPR training] 20 years ago, you still probably know a little bit more about doing good compressions than somebody who's never had it," he says.

"The bottom line is push hard and push fast," agrees Anderson, who says the recommended rhythm for chest compressions is to the beat of the 1970s Bee Gees hit "Stayin' Alive."

But even someone who lacks training can do CPR, says Kupas.

"We find more and more of this bystander CPR being done [after] on-the-fly training by the dispatcher," he says.

"They're just reading from a script — 'place your hand right in the center of the chest between that nipple line, press down and up, and then they start counting for them,'" he says.

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