COVID- It can take a long time for 19 patients on ventilators to regain consciousness. New research suggests that these delays may have a purpose: they protect the brain from oxygen deprivation.
The existence of such a brain-preserving state may explain why some patients wake up days or even weeks after ceasing ventilation, and it suggests that physicians should account for these lengthy recovery times when determining a patient’s prognosis.
The researchers link the pattern seen among those who have survived severe COVID-19 with similar delays known to occur in a small percentage of cardiac arrest patients in a study published November 7 in the Proceedings of the National Academy of Sciences.
“The COVID-19 patients’ delayed recoveries are very similar to the rare cases we’ve documented in previous research.” “In this new paper, we describe a mechanism to explain what we’re seeing in both types of patients,” said study co-senior author Dr. Nicholas D. Schiff, the Jerold B. Katz Professor of Neurology and Neuroscience at Weill Cornell Medicine and co-director of the Consortium for the Advanced Study of Brain Injury (CASBI).
He discovered evidence for this explanation — that patients’ brains are protecting themselves — in animals that can tolerate prolonged periods without oxygen, most notably painted turtles.
Dr. Schiff and his colleagues first observed these delays in comatose cardiac arrest patients who received cooling therapy to reduce brain damage caused by a loss of blood flow more than a decade ago. In one such case, a 71-year-old patient took 37 days to awaken before recovering nearly completely.
Dr. Schiff, a neurologist at NewYork-Presbyterian/Weill Cornell Medical Center, performed neurology consultations for COVID-19 patients during the pandemic, and he soon noticed similar, delayed awakenings occurring when patients were taken off ventilators and stopped receiving the sedatives given to them to reduce their movement.
Dr. Schiff and his colleagues, including co-author of the current paper, Dr. Emery N. Brown, professor of anaesthesia at Harvard Medical School, Edward Hood Taplin Professor of Medical Engineering and Computational Neuroscience in The Picower Institute for Learning and Memory at MIT, and an anesthesiologist at Massachusetts General Hospital, performed a separate analysis of a large cohort of Covid-19 patients from Weill Cornell Medicine and two other major U.S. medical centres. The longer the delay, the more oxygen deprivation they experienced while on the ventilator.
In a previous study of cardiac patients, the researchers discovered a distinct pattern in brain activity, which was also observed in patients undergoing deep anaesthesia. (There are very few recordings from COVID-19 patients.) Dr. Schiff discovered a similar pattern in the brains of painted turtles, which can survive up to five months without oxygen under ice in the winter. To accomplish this, they activate the same inhibitory system within the brain that is targeted by anaesthetics administered to human cardiac and COVID-19 patients, but in novel ways developed by evolutionary specialisations.
Dr. Schiff and Dr. Brown propose that the same protective response emerges in the patients by chance.
Dr. Schiff said, “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. Brown added, “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”.
When patients fail to regain consciousness for an extended period of time, doctors may recommend discontinuing life-sustaining care. For cardiac patients, this threshold is typically set at 14 days or less, whereas no such guidelines exist for COVID-19.