What Happens to Consciousness During Cardiac Arrest?

When the heart stops, a person is unresponsive. For a long time, doctors assumed that this meant the person was entirely unconscious. A group of studies led by Dr. Sam Parnia has asked whether that is always true. This article describes what they found and what they did not.

What are the AWARE studies?

Large studies of what patients experience during cardiac arrest. PulmCCM reports that the first AWARE study, published in 2014, covered 2,060 cardiac arrests at 15 U.S. and European centers. Of 140 survivors interviewed, 55 reported detailed memories and 9 reported near-death experiences. A follow-up, AWARE II, was published in the journal Resuscitation in 2023, after being presented at an American Heart Association meeting in 2022.

What did AWARE II find in patients?

Most did not survive. ScienceAlert reports that among 567 patients, 213 regained a pulse, 53 survived to leave the hospital, and only 28 were well enough to be interviewed. Of those 28, 11 (39 percent) reported memories of the time of the arrest, according to MDedge. PulmCCM adds that 21 percent described their death as a transcendent, “out of body” kind of experience.

What did the brain monitors show?

Surprising electrical activity. ScienceAlert says that 40 percent of survivors had relatively normal or near-normal brain recordings (EEG) up to an hour into CPR. MDedge reports that despite low oxygen in the brain, researchers saw gamma, delta, theta, alpha, and beta rhythms. Some of these brain waves normally occur when people are conscious and doing things like thinking and remembering. Dr. Parnia says doctors had long thought the brain suffers permanent damage about 10 minutes after the heart stops, but the study found electrical recovery well into ongoing CPR.

Did patients perceive anything in the room?

Not that the study could show. ScienceAlert says the team used a tablet and headphones with 365 patients during CPR, presenting images and sounds to see whether anyone, though unresponsive, might perceive them. Of the 28 patients interviewed, none recalled the images or the sounds. A few did recall things like chest compressions, electrodes on the skin, and voices.

What do outside experts say?

That it is interesting, but not conclusive. PulmCCM notes that AWARE II was the first study to show that normal EEG patterns are common during cardiac arrest, which strongly suggests some form of consciousness. But only two of the 28 interviewed patients had EEG data, and neither recalled anything. No one with those EEG patterns both survived and reported memories. An outside expert quoted by MDedge called the observation fairly remarkable, but said that whether there is conscious perception is very hard to answer.

What does it mean for how we think about death?

That the line between life and death is not a switch. Dr. Parnia has said that brain cells do not die immediately but over many hours. For the medical side, see Clinical Death vs. Biological Death and What Does the Brain Experience When We Die?. For what survivors report, see What People Commonly Report During a Near-Death Experience.