Illustration: Chiara Vercesi

New Clues to Coma Recovery


COVID-19 patients placed on ventilators can take a long time to regain consciousness. New research from Weill Cornell Medicine, NewYork-Presbyterian, MIT, and Massachusetts General Hospital is now illustrating that these delays may serve a purpose: protecting the brain from oxygen deprivation.

The existence of such a brain-preserving state could explain why some patients wake up days or even weeks after they stop receiving ventilation, and it suggests that physicians should take these lengthy recovery times into account when determining a patient’s prognosis. 

“The delayed recoveries in COVID-19 patients are very much like the rare cases we’ve documented in previous research,” says Weill Cornell Medicine neuroscientist Dr. Nicholas D. Schiff, co-senior author of a study that appeared in Proceedings of the National Academy of Sciences last November. In the study, the investigators connect the pattern seen among those who have survived severe COVID-19 with similar delays known to occur in a small fraction of cardiac arrest patients. “We describe a mechanism to explain what we’re seeing in both types of patients,” Dr. Schiff says.

Beginning more than a decade ago, he and his colleagues first observed these delays among comatose cardiac arrest patients who received cooling therapy to reduce brain damage caused by a loss of blood flow. In one such case, a 71-year-old patient took 37 days to awaken before ultimately making a near-complete recovery.

In a 2020 study of three such patients, the researchers recorded a distinctive pattern in brain activity, one also seen in patients under deep anesthesia. (Recordings from COVID-19 patients are extremely limited.) Dr. Schiff read about a similar pattern that had been seen in the brains of painted turtles, which can withstand up to five months without oxygen under ice in the winter. To do so, they activate the same inhibitory system within the brain targeted by anesthetics given to human cardiac arrest and COVID-19 patients but in novel ways developed by evolutionary specializations.

In their recent study, Dr. Schiff and co-author Dr. Emery N. Brown (who holds faculty affiliations at Harvard Medical School, MIT, and Massachusetts General Hospital), propose that, by chance, the same protective response emerges in the patients. 

“It is our theory that oxygen deprivation as well as practices in the ICU, including commonly used anesthetics, expose elements of strategies that animals use to survive in extreme conditions,” Dr. Schiff says.

“These observations may offer new insights into the mechanisms of how certain anesthetics produce unconsciousness and new approaches for ICU sedation and for fostering recovery from disorders of consciousness,” Dr. Brown adds.

When patients fail to regain consciousness for an extended time, physicians may recommend withdrawing life-supporting care. This threshold is typically set at 14 days or less for cardiac patients, while no such guidelines exist for COVID-19.

In light of this new research, however, so long as they lack brain injuries, physicians should avoid making negative projections about these patients’ potential to recover, the researchers say.

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