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A simple measurement using a device available in every hospital could distinguish brain damaged patients who are likely to “wake up” from those who are not, scientists reported on Thursday.

Predicting which unconscious patients will remain that way forever and who is likely to recover is so difficult that even expert physicians get it wrong in about 40 percent of cases, said Dr. Nicholas Schiff of Weill Cornell Medical Center in New York City, who was not involved in the new study.

As a result, tens of thousands of patients are discharged from hospitals and “shunted off to nursing homes and other institutions” where they are treated as living corpses, kept alive but given no therapy that might bring them back to conscious life, Schiff said.


The new study, which he called “rigorous and extremely well done,” offers a “direct, simple approach that could be adopted tomorrow.”

An estimated 200,000 to 300,000 people in the United States are living in that gray area between life and death — either in an unresponsive wakefulness state (previously called a vegetative state) or a minimally conscious state. In the former, people look awake but are wholly unaware of their surroundings and do not consciously respond to sights, sounds, or touch. Those in a minimally conscious state sometimes respond to a command or other stimulus, but often do not — hence the difficulty in distinguishing the two. But the latter are much more likely to regain consciousness.


Diagnosing via behavioral measures is “susceptible to interpretational bias,” said Ron Kupers. So he along with colleagues at the University of Copenhagen set out to “find more objective measures” to distinguish these two states. They used positon emission tomography, or PET, imaging, which measures brain metabolism, to try to distinguish brains that appeared equally unconscious but that might have different capacities for recovery.

The scientists tested the technique on 131 brain-injured patients: 49 in a vegetative state, 65 who were minimally conscious, and 17 who were emerging from a minimally conscious state. No single region was associated with likelihood of regaining consciousness — that is, the brain does not have a “consciousness center.”

But overall metabolism did show a difference. Vegetative patients had, on average, 38 percent of the brain activity that healthy people did. Minimally conscious patients had 56 percent, the researchers report in the journal Current Biology.

The technique missed only 5 percent of the minimally conscious patients (in statistics-speak, it had a sensitivity of 95 percent). It incorrectly identified as minimally conscious only 22 percent of patients who weren’t (its specificity was 78 percent).

Especially compared to how physicians currently make that distinction, said Cornell’s Schiff, “that’s good enough for prime time.”

Arguably even more important, PET predicted whether a patient would recover awareness within a year. The cutoff: Brain activity at least 41 percent of that in healthy people. Using that rule of thumb researchers correctly identified 94 percent of the patients who would recover within 12 months.

That suggests that at a high enough metabolism, the brain flips from one fundamental state (unconsciousness) to another (consciousness) rather than changing gradually.

A previous study by some of the same researchers had found that PET scans could correctly predict regained consciousness 74 percent of the time. This study improved upon that rate.

And this new, more precise metric holds much more promise for patient care. Expert panels have repeatedly called for wholly or partly unconscious patients to be reevaluated every few weeks to see if they might be regaining awareness. But most insurance plans don’t cover that, said Schiff, so it doesn’t happen.

The new study “takes away the argument that we don’t know,” Schiff said. “It’s a game changer.”