For the most part, patients in a coma have lost their thinking abilities and are oblivious to their surroundings. But those in a vegetative state often give the impression of emerging from a coma. Unlike a patient in a full coma, they’re in a state of partial arousal, but still lack full awareness.
The new test, which is already available in virtually every hospital, will make it easier for doctors to assess the nature and severity of comas.
“In nearly all cases, whole-brain energy turnover directly predicted either the current level of awareness or its subsequent recovery,” said Ron Kupers of the University of Copenhagen and Yale University in a statement. “In short, our findings indicate that there is a minimal energetic requirement for sustained consciousness to arise after brain injury.”
To reach this conclusion, Kupers and his colleagues quantified and mapped cerebral sugar metabolism in 131 brain-injured patients, all of whom were suffering from either full or partial loss of consciousness. Using a well-known imaging technique known as FDG-PET, they were able to capture and map glucose uptake in the brain.
Results showed that a patient’s behavioural response was strongly linked to their overall cerebral energy turnover. Patients with a glucose metabolism below 42 per cent of normal activity appeared to be fully unconscious and never recovered consciousness after a year.
But those who had brain metabolic activity above this critical threshold either displayed signs of partial awareness, or had awoken from their unconscious state a year later. Overall, the cerebral metabolic rate accounted for the imminent return of awareness in 94 per cent of patients.
“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. “We were not able to test this hypothesis directly, but it provides a very interesting direction for future research.”
The scientists say that it’ll be important for other researchers to verify their findings in other sets of patients. Until then, they’re going to investigate how brain metabolism changes over time in brain-injured patients.