How Long Can the Brain Survive Without Oxygen?
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Up to an hour after their hearts had stopped, some patients revived by cardiopulmonary resuscitation (CPR) described clear memories of experiencing death that occurred while they were seemingly unconscious, according to a study published online September 14, 2023, in the journal Resuscitation.
Investigators also found that 40 percent of the patients who received brain monitoring during CPR showed brain activity consistent with consciousness — in some cases, even after 60 minutes of resuscitation. The electroencephalogram (EEG) readings of participants showed spikes in the gamma, delta, theta, alpha, and beta waves, all associated with higher mental function despite significant oxygen deprivation to the brain.
“Although doctors have long thought that the brain suffers permanent damage about 10 minutes after the heart stops supplying it with oxygen, our work found that the brain can show signs of electrical recovery long into ongoing CPR,” said senior study author Sam Parnia, MD, PhD, an associate professor in the department of medicine at NYU Langone Health in a press release.
“This is the first large study to show that these recollections and brain wave changes may be signs of universal, shared elements of so-called near-death experiences,” added Dr. Parnia.
Researchers Monitored Dying Patients Prospectively in Hospitals Across the U.S. and U.K.
Although previous studies have suggested that there must be some consciousness or awareness going on during cardiac arrest, much of what happens — or doesn’t — remains a mystery.
A study published earlier this year in the study published earlier this year in the Proceedings of the National Academy of Science provided the strongest evidence to date that some kind of consciousness remains for a short time after the heart stops beating and a person is considered dead.
To further explore what happens between life and death, researchers at NYU Grossman School of Medicine, along with 25 mostly U.S. and British hospitals, devised a way to collect data from people whose hearts stop beating — a challenge that required a significant amount of planning and coordination.
Team members were alerted in real time via pager when a hospitalized patient’s heart stopped. While medical staff performed CPR, scientists tested the subject for visual and auditory awareness and, if CPR went on long enough, set up equipment to measure electrical activity.
Over a two-year period, there were over 2,000 events in the participating hospitals, and 567 patients who could be included, and of those, 53 (9.3 percent) survived.
The reasons why patients were not included were often related to team members not being able to get there in time — within roughly five minutes, said Parnia in a presentation about the study at the 2022 American Heart Association Resuscitation Science Symposium.
The fact that those included needed to have five minutes of CPR or much longer (not quick shocks that immediately revived them) accounts for the low survival rate of those in the trial, he added.
Survivors Who Appeared Nonresponsive Had Memories of Death Experience
Of the 53 patients who were brought back to life, 28 people were well enough to be interviewed about what they experienced during CPR. Although none of them had shown external signs of consciousness during CPR, 11 of those people (39 percent) reported memories of the event.
To supplement the available information, additional narratives from 126 community survivors of cardiac arrest with self-reported memories were also examined to provide greater understanding of the themes related to the recalled experience of death.
Survivors Recount Reliving Memories and Reevaluating Life
The experiences were organized into common themes, which included consciousness emergence during CPR, dream-like experiences, and recalled experiences of death (RED), in which survivors report themes like separation from the body, a purposeful reevaluation of life, and returning to a comforting home or home-like place.
Among those who had recalled the experience of death, Parnia highlighted the following comments from different participants during his AHA presentation.
- “I was given a life review. During the review, we revisit scenes from our lives.”
- “I saw my entire life in great detail and experienced feelings through it of satisfaction, shame, and repentance.”
- “All my memories folded back into my head, what I had done and what I thought.”
- “I saw things in rapid succession that were moments of my life.”
Authors Suggest Lack of Blood Flow to Brain Allows Access to ‘Entire Consciousness’
The brain activity captured via EEG along with the participants’ recalled experiences show that some people have a clear hyperconscious experience where they reevaluate their life in a way that’s different from hallucinations or other imaginary experiences, said Parnia.
“We were able to also identify the mechanism by which this experience occurs, which is that as the brain shuts down, because of a lack of blood flow in death, the normal braking systems in the brain are removed, known as disinhibition. This enables people to have access to their entire consciousness, or their thoughts, memories, all their emotional states, everything they’ve ever done, which they relive through the perspective of morality and ethics,” he said.
This study is a very interesting because it investigates both quantitative measurements of cerebral physiology (like regional oxygen saturation and EEG) and qualitative experiences during in-hospital cardiac arrest, says Karen Hirsch, MD, an associate professor of neurocritical care in the department of neurology at Stanford University in California.
“Only a very small percentage of patients survived to hospital discharge (9 percent) and even fewer patients participated in interviews, and so it is important to note that this is a limited sample,” says Dr. Hirsh, who researches cardiac arrest but was not associated with this study. “All that said, this study provides interesting data about what cardiac arrest patients experience and/or recall about their cardiac arrest experience.”
Findings Could Pave the Way for Potential Treatments to Preserve the Brain When the Heart Stops
There are two key takeaways for what these means for patient care and future research, said Parnia in the video interview.
The study’s observation that the brain can respond and show signs of normal activity even up to an hour into CPR demonstrates that the common misperception that the brain dies after 5 or 10 minutes of oxygen deprivation is incorrect, and actually the brain remains quite robust, he said.
“This opens up the ability to create new treatments, new drugs that can preserve the brain and enable us to bring them back to life to the full consciousness in the future,” said Parnia.
These findings also provide further insight into what happens to the human mind and consciousness as people are going through life and death, he said. “This will have very big ramifications for many disciplines, including end-of-life care for patients and also the field of transplantation, as we take organs from people to give life to others. We need to understand what happens between life and death,” said Parnia.
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