What you need to know about unresponsive wakefulness

— -- In a Thursday press conference, doctors at UC Health said 22-year-old Otto Warmbier, who this week returned to the U.S. after being held in North Korea for 17 months, is currently in a state of “unresponsive wakefulness” -- characterized by a lack of awareness of one’s environment and self despite being awake.

The cause of this condition, according to UC Health’s Dr. Daniel Kanter, was "extensive loss of brain tissue in all regions" -- a situation his team believes resulted from cardiopulmonary arrest, which would have impeded the supply of oxygen to the cells of his brain.

Below is more about Warmbier’s condition -- and what doctors suspect regarding its origin.

What is unresponsive wakefulness?

Unresponsive wakefulness syndrome -- which doctors previously referred to as a persistent vegetative state or a vegetative state -- is best described as a state in which a patient may have certain characteristics of consciousness, such as eye blinking and eye movement, but who has no apparent reaction to the external world or understanding of or engagement with their surroundings.

However, the main regulatory functions of the body -- like sleep cycles, breathing, digestion and internal body temperature control -- remain intact to some degree, depending on the patient. This is because areas of the brain that control these functions are often still working. A patient can be intermittently awake, continue to breathe on his or her own, spontaneously open his or her eyes, and look around in a non-purposeful way.

Unresponsive wakefulness should not be confused with a coma, in which a patient is not awake. Patients with unresponsive wakefulness are technically awake, as the name implies.

What caused Warmbier's unresponsive wakefulness?

Doctors speaking at the press conference said Warmbier's medical condition appears to suggest that his brain, at some point, was deprived of oxygen, which subsequently led to the death of brain tissues. They noted that one possibility was cardiopulmonary arrest -- a problem with the heart or lungs that prevents the delivery of oxygenated blood to the brain. The resulting brain injury, over time, likely led to his state of unresponsive wakefulness.

As for what circumstances might have led to this cardiopulmonary arrest, doctors said there are so many possible causes that they cannot speculate as to the exact nature of his injury.

How do doctors determine if a patient has unresponsive wakefulness?

A neurologist -- a physician specializing in brain, spinal cord and nerve disorders -- can determine whether a patient has unresponsive wakefulness syndrome. This doctor will conduct numerous examinations to determine whether the patient truly lacks awareness of self and of the environment, as well as whether he or she lacks purposeful and voluntary responses to sight, sound, touch or pain. The neurologist will also look for a lack of language expression and comprehension, and a lack of bowel and bladder control.

How long can unresponsive wakefulness last?

Depending on the medical circumstances that led to the unresponsive wakefulness, it can be transient, persist up to a year, or be permanent.

What is the prognosis for someone with unresponsive wakefulness?

Doctors at UC Health declined to share details on Warmbier’s prognosis, citing the wishes of his family. From past research, however, we know that the less time a patient spends in this state, the better their prognosis and chance for recovery. Those who are young and who experience traumatic brain injury (as opposed to nontraumatic injury) also tend to have a better prognosis. However, recovery is unlikely for patients who remain in a state of unresponsive wakefulness for longer than 12 months.

Priya Raja is a medical fellow in the ABC News Medical Unit as a part of the Stanford - ABC News Global Health and Media Fellowship. She is also a rising third-year medical student at The University of Texas Southwestern Medical Center.

Hong-An Nguyen, M.D., is a third-year resident physician in pediatrics at New York-Presbyterian/Columbia University Medical Center.