July 2, 2019

For years, doctors have known brain injury patients who are otherwise unresponsive can experience "hidden consciousness"—or brain response to outside stimuli that's detectable by MRI or EEG, but a new study from researchers at Columbia University and NewYork-Presbyterian Hospital suggests those signs of consciousness could be used to predict patient recovery.

What is 'hidden consciousness'?

Researchers identified so-called "hidden consciousness" more than a decade ago. The term refers to patients with brain injuries that have left them unresponsive but who have brain activity can be detected by MRI or electroencephalography (EEG). Over the past decade, researchers have used MRIs and EEG to identify signs of hidden consciousness in 14% of chronically unresponsive patients, according to a Columbia University release

Researchers believe that being able to identify hidden consciousness in unresponsive patients early on could improve their ability to predict long-term recovery, but the current method of detection, which largely relies on MRIs, can be hard to perform in critical care settings, according to the Columbia release.  

So a group of researchers from Columbia University and NewYork-Presbyterian Hospital decided to test if EEG data, which is used to diagnose epilepsy and other brain injuries, can be used to identify hidden consciousness shortly after injury and predict patients' recovery. They published their findings Thursday in the New England Journal of Medicine.  

Study details

To test their theory, researchers looked at 104 ICU patients who had suffered sudden brain injury from trauma, hemorrhage, or oxygen deprivation. Brain activity was measured a median of four days after the injury. None of the patients were paralyzed, but they were not able to talk and did not respond to verbal commands to move.

The researchers used headphone to play a recording of simple movement instructions, such as opening and closing their hands, and monitored their brain activity via an EEG.

One year later, the researchers followed up with the patients.

Key findings

The researchers found that within four days of injury, 15% of patients, or 16 out of the 104 examined, showed brain activity on the EEG when the recording was played, which the researchers wrote suggests they were experiencing hidden consciousness.

Of those patients, the researchers found 50% improved and could follow verbal commands prior to discharge. In comparison, 26% of patients who did not show signs of hidden consciousness improved and could follow verbal commands prior to discharge.

After one year, 44% of patients who'd shown signs of hidden consciousness could function independently for up to eight hours a day, compared with 14% of patients who had not shown signs of hidden consciousness.

The researchers observed that hidden consciousness signals were more common among patients who'd been injured by trauma or hemorrhage than those whose brain injuries came from oxygen deprivation. However, the study was not designed in a way that could determine the EEG analysis' predictive value among different sources of brain injury.

Clinical implications

The researchers noted that larger studies need to be done to determine the utility of EEG monitoring for predicting patient outcomes, but if the findings are confirmed, the research could be used to help doctors predict which patients will regain consciousness.

Jan Claassen, lead author of the new study and medical director of the neurological ICU at Columbia, said, "Though our study was small, it suggests that EEG—a tool that's readily available at the patient's bedside in the ICU in almost any hospital across the globe—has the potential to completely change how we manage patients with acute brain injury."

Nicholas Schiff, a professor of neurology and neuroscience at Weill Cornell Medical College, said the findings are "very big for the field."

Brian Edlow, associate director of Massachusetts General Hospital's Center for Neurotechnology and Neurorecovery, noted, "This approach is not perfect. … But this study suggests that there are compelling reasons to acquire these types of data. And it's not hard to imagine a future where ICU's routinely get these data and send them off for analysis" (Columbia release, 6/26; Torres, "Shots," NPR, 6/27; Thompson, HealthDay, 6/26; Classen et al., New England Journal of Medicine, 6/27; Carey, New York Times, 6/26).

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