How many people are conscious during CPR?
Enough that we should do it politely
It’s likely that some patients are to some extent conscious and aware during cardiac arrest and cardiopulmonary resuscitation (CPR), a limited but growing body of research suggests.
Clinicians have tended to conflate unconsciousness with unresponsiveness, in part because dictionaries define it so. Consciousness is being “aware and responding to one’s surroundings; awake.” (New Oxford American Dictionary.) But does it need to be all these?
Recent research has found physical unresponsiveness to be unreliable as a proxy for unconsciousness. A significant proportion of unresponsive, brain-injured patients retain some form of awareness and ability to respond cognitively (i.e., with contextually appropriate and apparently purposeful thoughts). Dubbed “covert consciousness,” this liminal state of existence is under investigation by a small community of researchers.
Patients experiencing cardiac arrest are unresponsive by definition and have likewise been presumed to be universally unconscious and unaware.
However, it appears that is not always the case.
Aware II Study
At 25 sites at multiple centers in the U.S. and the U.K., 567 patients experiencing in-hospital cardiac arrest lasting longer than 5 minutes had headphones placed and a tablet mounted in front of their eyes.
Two hundred thirteen initially survived their arrest (38%), 53 (9%) survived to discharge, and only 28 of them could complete interviews (5% of all arrests). Not one survivor recalled the material presented on the screen, and only one person identified the sound in the headphones.
However! At nine of the 25 sites, a small 4-lead EEG was also placed on 85 patients’ foreheads, recording brain activity during pauses in CPR. These produced readable data about half the time, and were combined with regional cerebral oximetry (near-infrared spectroscopy) to measure cerebral hypoxia.
Normal or near-normal EEG patterns consistent with consciousness (delta in 22%; theta in 12%; alpha in 6%; beta in 1%) occurred at up to 60 minutes of CPR, despite cerebral hypoxia (rSO2 ~40-50%).
The 28 survivors were also interviewed, and they reported recalling:
Memories of the experience of cardiac arrest generally (39%).
Experiencing their death as a transcendent (e.g., “out of body”) experience (21%).
Emerging from coma during CPR (experiencing compressions, etc) despite complete unresponsiveness (7%).
Although intra-cardiac arrest EEGs were often consistent with consciousness, and many patients recalled conscious experiences during arrests, only two of the 28 interviewed patients had EEG data available, and neither of those two patients recalled anything about CPR.
Many other studies report the frequency of self-reported awareness during CPR (commonly called near-death experiences), but such memories are by their nature subjective and unverifiable.
Aware I, et al
At 15 U.S. and European centers, 55 survivors of 2,060 cardiac arrests (out of 140 interviewed survivors) reported detailed memories, and 9 reported near-death experiences. One patient recalled floating above his body in the room, and accurately described people, activity, and sounds occurring during his resuscitation.
To give you a flavor of the “researcher vibes” in this study: as part of the design, 1,000 shelves were installed high on walls in the participating hospitals, with a distinctive image placed on each that could only be seen by a hypothetically floating spirit looking down. As it happened, 78% of cardiac arrests took place in rooms without a shelf, and no patient reported seeing one of the shelved images.
Numerous other studies report about ~10% of cardiac arrest survivors recall memories or near-death experiences of the event. Certain themes recur: tunnels, bright lights, observing one’s body from above. However, these personal reports emerge in interviews occurring as long as months after the arrest, and confabulation is impossible to exclude.
Gamma Bursts and Pig Brain-in-a-Jar
In an ex vivo extracorporeal experimental system, pig brains can be severed, explanted into an oxygenated, circulating cytoprotective solution, where they can maintain or recover many normal functions, including synaptic activity and metabolism, for up to four hours.
Immediately after experimentally induced cardiac arrest, mammals can demonstrate a surge of EEG activity that includes gamma oscillations organized in “functional connectivity” patterns considered to be consistent with consciousness.
Xu et al observed this pattern in two of four patients dying after withdrawal of life support. During continuous EEG monitoring, “both patients displayed surges of functional and directed connectivity at multiple frequency bands within the posterior cortical ‘hot zone,’ a region postulated to be critical for conscious processing.”
Discussion
Many explanations for near-death experiences have been proposed that don’t require a disembodied consciousness: cerebral hypoxia with disinhibition, REM sleep intrusion, neurotransmitter flooding, among others.
The least metaphysical of the cardiac arrest memories occur when a patient emerges from coma as cerebral perfusion is restored, and ordinary perceptions and memory-making resume.
Aware-II is the first study to show normal EEG patterns are commonly present during cardiac arrest. This strongly suggests some form of consciousness, but no one with these EEG patterns both survived and reported any memories of the arrest.
There’s no reason to disbelieve near-death experiences, but they would be more convincing if correlated with EEG patterns consistent with consciousness during cardiac arrest. Because of the low survival rate of cardiac arrest, such a study will be difficult to perform, but Aware-II shows it is possible.
We know one thing for sure: the brain doesn’t have an on/off switch. Although most patients who are unresponsive are also unconscious, research now provides intriguing evidence of a spooky, in-between place, a Bardo if you like, that defies our conventional understanding of consciousness.
At the moment that patients are at their most dehumanized, suffering under the blunt trauma of CPR, there is a distinct possibility that some of them are in the midst of a deeply human experience, which for most will be their last.
I’m not sure if that makes it all more beautiful, or unbearable.
References
Parnia S, Keshavarz Shirazi T, Patel J, et al. AWAreness during REsuscitation - II: A multi-center study of consciousness and awareness in cardiac arrest. Resuscitation. 2023 Oct;191:109903. doi: 10.1016/j.resuscitation.2023.109903. Epub 2023 Jul 7. PMID: 37423492.
Xu G, Mihaylova T, Li D, et al. Surge of neurophysiological coupling and connectivity of gamma oscillations in the dying human brain. Proceedings of the National Academy of Sciences. 2023;120(19). doi:https://doi.org/10.1073/pnas.2216268120
Vrselja Z, Daniele SG, Silbereis J, et al. Restoration of brain circulation and cellular functions hours post-mortem. Nature. 2019;568(7752):336-343. doi:https://doi.org/10.1038/s41586-019-1099-1