Brain and Body

A Simple Test Can Predict Which Coma Patients Will Wake Up With 94% Accuracy

May 27, 2016 | Kelly Tatera

Woman lying in hospital bed
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Within a one-year time period.

Not knowing if or when a loved one will come out of a coma is an agonizing experience for anyone involved, and since all brains work differently, it’s difficult for doctors to predict which patients will come out of their vegetative states.

Now, researchers have discovered a way to test whether patients who have lost consciousness are likely to wake up within a year or not, which could provide families and friends with at least some indication about what to expect.

Reporting in the Cell Press journal Current Biology, the scientists found that the amount of glucose (sugar) consumed by the brain can directly predict a person’s level of awareness and likelihood that he or she will recover awareness within a year.

"In nearly all cases, whole-brain energy turnover directly predicted either the current level of awareness or its subsequent recovery," Ron Kupers, of the University of Copenhagen and Yale University, said in a press release.

Kupers and colleagues came to this discovery using a type of positron emission tomography (PET) scan that measures how much sugar is being metabolized in the brain. The well-known imaging technique, FDG-PET, is already used in many hospitals to monitor cancer progression, and works after glucose labelled with radioactive tracer molecules is injected into the bloodstream.

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The team, aiming to develop more reliable diagnostic markers for assessing levels of consciousness, mapped the brains of 131 brain-injured patients who were suffering from either full of partial loss of consciousness. They measured the metabolism of neurons in these patients and then compared the results to whether or not the patient had woken up within a year.

The results revealed that patients who showed less than 42 percent of normal brain activity didn’t regain consciousness in a year’s time, while those who had over that amount woke up within a year.

"In short, our findings indicate that there is a minimal energetic requirement for sustained consciousness to arise after brain injury," explains Kupers.

Overall, the researchers were able to accurately predict 94 percent of the patients who would wake up from a vegetative state.

"The discovery of a clear metabolic boundary between the conscious and unconscious states could imply that the brain undergoes a fundamental state change at a certain level of energy turnover, in a sense that consciousness 'ignites' as brain activity reaches a certain threshold," said study co-author Johan Stender.

Stender says that the researchers weren’t able to test this hypothesis directly in this study, but it provides an interesting direction for future research.

Although the findings are exciting, the researchers say it’s important for future research to confirm them. They also hope to delve into how brain metabolism changes over time in brain-injured patients.

"The take-home message [for now] is that consciousness is a highly energy demanding process, involving the brain at large," Kupers says. "This fundamental physiological trait can help clinicians determine the potential for recovery of awareness in patients suffering from severe brain injuries of any kind.

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