COVID-19 patients placed on ventilators can take a long time to regain consciousness. New research 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.

In a study published 7 No­vember in the Proceedings of the National Academy of Scienc­es, 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.

A mechanism to explain

“The delayed recoveries in COVID-19 patients are very much like 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 in the Feil Family Brain and Mind Research Institute and co-director of the Consortium for the Advanced Study of Brain Injury (CASBI) at Weill Cornell Medicine.

He found evidence for this explanation — that patients’ brains are protecting them­selves — in animals, most no­tably painted turtles, that can tolerate extended periods with­out oxygen.

More than a decade ago, Dr. Schiff 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.

Neurology consultations

During the pandemic, Dr. Schiff, who is also a neurolo­gist at NewYork-Presbyterian/ Weill Cornell Medical Centre, performed neurology consulta­tions for COVID-19 patients, and he soon began seeing similar, delayed awakenings occurring when patients were taken off ventilators and stopped receiv­ing the sedatives given to them to reduce their movement.

In a separate analysis of a large cohort of Covid-19 patients from Weill Cornell Medicine and two other major US medical centres, Dr. Schiff and his col­leagues, including co-author of the current paper, Dr. Emery N. Brown, professor of anesthesia 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, found that a quarter of patients who survived ventilation took 10 days or longer to recover consciousness. The more oxygen deprivation they suffered while on the ventilator, the longer that delay.

A distinctive pattern

In the prior study of car­diac 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 that a similar pattern 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 and COVID-19 patients but in novel ways developed by evolutionary specializations.

Dr. Schiff and Dr. Brown 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 said.

New insights into the mech­anisms

“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 added.

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.

SOURCE: ANI