Doctors across the world are noticing a mysterious and disturbing phenomenon when some COVID-19 patients are removed from ventilators. After intubation, they remain unconscious for days, weeks, or longer. The unofficial term for this state is "prolonged" or "persistent" coma.

According to NPR, some families have asked that their stricken loved ones be removed from life support because of the unknown duration of the coma and the potential for neurological damage.

"Because this disease is so new and because there are so many unanswered questions about COVID-19, we currently do not have reliable tools to predict how long it will take any individual to recover consciousness," Dr. Brian Edlow, an expert in coma recovery at Massachusetts General Hospital, told NPR. Edlow added that there is no way of knowing how patients will come out of a coma with an acceptable quality of life.

Experts theorize that there are several reasons why some patients remain comatose after intubation. COVID-19 patents need more sedation while on ventilators and spend more time being intubated than patients suffering from other diseases that cause pneumonia. The disease itself can result in lower levels of oxygen being delivered to the lungs, which can cause brain damage, according to NPR.

Experts say that approximately every fifth patient admitted to the ICU has some degree of unconsciousness. A group of researchers at the University of Pittsburgh is studying the data on how COVID-19 impacts the brain, including the problem of comas. Patients who eventually do regain consciousness often suffer from cognitive problems.

In the spring, researchers created a multidisciplinary COVID-19 Coma Board to track and study cases of patients affected by this rare but serious consequence of the disease.

Scientists have reported other unusual neurological side effects from COVID-19 as well.

Neurologists have found that patients testing positive for the coronavirus have come into hospitals with potentially serious nervous system complications such as a rare disease called Guillain-Barre Syndrome.

According to The Conversation, studies show that Guillain-Barre Syndrome often emerges following bacterial and viral infections. If not diagnosed early, the autoimmune disease can cause weakness and even paralysis of muscles throughout the body, including the muscles we need to breathe. This can necessitate the use of a ventilator for severely ill patients.

"This is a profound problem for which there are fundamental gaps in our knowledge," Edlow told The Washington Post. "It could affect many, many people."