A study examining individuals who survived cardiac arrest revealed that approximately one-third reported memories and perceptions during this period, suggesting consciousness. Some recounted regaining consciousness during or after cardiopulmonary resuscitation, while others described dream-like or transcendent experiences related to death. Importantly, the research team also found that the brain can exhibit signs of activity even after the heart has ceased to beat. The study was published in Resuscitation.
Cardiac arrest is when the heart suddenly stops beating. It is typically caused by an electrical disturbance in the heart that disrupts its normal pumping rhythm. When this happens, the blood flow to vital organs, including the brain, stops. This can result in unconsciousness and death if not promptly treated. Cardiac arrest differs from a heart attack, which is caused by a blockage in the blood vessels supplying the heart muscle.
In the United States, between 350,000 and 750,000 people experience cardiac arrest annually, with only about 10% surviving. Although individuals in cardiac arrest typically appear unconscious, about one-third of survivors report conscious experiences during this period. Previous studies have been inconclusive in determining whether these experiences reflect actual awareness of their surroundings.
Study authors Sam Parnia and his colleagues wanted to examine the cognitive experiences of survivors of cardiac arrest. They wanted to categorize the types of experiences reported, but also establish electroencephalography biomarkers that would show whether and when a person in cardiac arrest is emerging from coma and becoming conscious. The authors of this study hoped that this would help them determine when such a person is experiencing lucid cognitive activity as well.
The research team identified 567 patients who suffered cardiac arrest in 25 hospitals. During resuscitation, they placed a tablet computer and headphones on the patients, displaying images and playing sounds (e.g., words for fruits like apple, pear, and banana), to test for post-arrest memory recall.
Of these individuals, medical staff were able to restore circulation in 213 of them, but only 53 or a bit over 9% survived long enough to be discharged from the hospital. Survivors of cardiac arrest were more often male than female and younger. Cardiopulmonary resuscitation lasted 26 minutes on average, but individual duration varied a lot.
Interviews were conducted with 28 survivors about their conscious experiences during cardiac arrest. Eleven reported memories and perceptions indicative of consciousness, despite showing no external signs of consciousness like groaning or moving. These experiences included emerging from coma during or after resuscitation, and dream-like or transcendent experiences.
The experiences reported by these 11 individuals could be grouped into four categories: 1.) emerging from coma during or 2.) after resuscitation, 3.) dream-like experiences, and 4.) recollections of death. An additional 126 survivors were interviewed, revealing similar experiences, plus delusional misinterpretations of medical events. For instance, the sensation from an intravenous line was misinterpreted as burning in hell.
Participants who emerged from coma during resuscitation typically described the impact of the procedure on their bodies. They talked about feeling electrodes, pain, pressure, bouncing from chest compressions or hearing conversations by clinicians during this period. Those who emerged from coma after resuscitation typically talked about memories from the intensive care unit.
Individuals who recalled experiences of death talked about perceptions of separation from the body, often with a recognition that they have died, having visual awareness of the situation from the perspective of people doing the resuscitation, doing a purposeful and educational reevaluation of their life and returning to a place like home. These experiences were typically completed with a decision to return to their bodies.
Dreamlike experiences included visions of rainbows, fish, igloo, humanoid beings, wooden houses and other themes. However, researchers could not identify commonalities in these experiences and they did not seem to follow a story arc.
The researchers also conducted a substudy involving brain monitoring using EEG, or electroencephalography, a method used to record the electrical activity of the brain. EEG data were collected from 85 subjects during CPR, but only 53 of these had interpretable EEG data due to issues like electrical interference and motion artifact.
The EEG data showed various patterns. Predominantly, there was an absence of cortical brain activity (suppressed EEG) in 47% of the data/images. Seizure-like (epileptiform) activity was observed in about 5% of the data/images. Importantly, signs of near-normal or physiological EEG activity consistent with consciousness were also observed, including delta and theta activity in 22% and 12% of the data/images respectively, alpha activity in 6%, and beta activity in 1%.
In a subset of patients, brain activity returned to normal, or nearly normal, from a flatline state during CPR, as indicated by the presence of gamma, delta, theta, alpha, and beta waves associated with higher mental function. This occurred in nearly 40% of the patients and was observed up to 35–60 minutes into CPR. This is the first report of such biomarkers of consciousness during cardiac arrest and CPR.
“While unrecognized, people undergoing cardiac arrest may have consciousness, awareness and cognitive experiences despite absent visible signs of consciousness. Although systematic studies have not been able to absolutely prove the reality or meaning of patients’ experiences and claims of awareness in relation to death, it has been impossible to disclaim them either. The recalled experience surrounding death now merits further genuine empirical investigation without prejudice,” the study authors concluded.
The study sheds light on possible conscious experiences of individuals undergoing cardiac arrest. However, it should be noted that the results are based only on experiences of individuals who survived cardiac arrest while remaining in sufficiently good health to give interviews. In addition, none of the 28 interviewed survivors recalled the images presented during cardiac arrest, and only one recalled the sounds.
The paper, “AWAreness during REsuscitation – II: A multicenter study of consciousness and awareness in cardiac arrest”, was authored by Sam Parnia, Tara Keshavarz Shirazi, Jignesh Patel, Linh Tran, Niraj Sinha, Caitlin O’Neill, Emma Roellke, Amanda Mengotto, Shannon Findlay, Michael McBrine, Rebecca Spiegel, Thaddeus Tarpey, Elise Huppert, Ian Jaffe, Anelly M. Gonzales, Jing Xu, Emmeline Koopman, Gavin D. Perkins, Alain Vuylsteke, Benjamin M. Bloom, Heather Jarman, Hiu Nam Tong, Louisa Chan, Michael Lyaker, Matthew Thomas, Veselin Velchev, Charles B. Cairns, Rahul Sharma, Erik Kulstad, Elizabeth Scherer, Terence O’Keeffe, Mahtab Foroozesh, Olumayowa Abe, Chinwe Ogedegbe, Amira Girgis, Deepak Pradhan, and Charles D. Deakin.
