EEG can detect hidden consciousness just days after brain injury

EEG data reveals nearly one in seven ICU patients with brain injuries shows evidence of hidden consciousness just days after injury, and that these patients are more likely to recover.

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Currently, clinicians use bedside neurological examinations, imaging and electrophysiological examinations to predict the likelihood of recovery for unconscious, brain-injured patients. However, this is frequently inaccurate.  

MRI and EEG studies have shown hidden consciousness in 14% of chronically unresponsive patients. MRI is challenging to perform in a critical setting; however, EEG may be an easy and fast way to identify signs of hidden consciousness.

An EEG study, which was published in New England Journal of Medicine, focused on 104 patients in an intensive care unit who had recently sustained a sudden brain injury due to hemorrhage, trauma or oxygen deprivation. None of the patients were paralyzed, however, they were unable to talk and did not respond to commands to move. 

Each day, in addition to standard neurological exams, the patients were asked multiple times to open and close their hands or stop opening and closing their hands. The team then used a machine learning technique to analyze the EEG data to look for signs that the patients detected a difference between the commands.

Researchers noticed a reproducible different pattern of activity between the commands, suggesting patients were able to understand the difference between the commands. Within 4 days of the injury 15% of the still unresponsive patients had brain activity on at least one EEG recording. Among the patients with these patterns, 50% improved and were able to follow verbal commands before being discharged from hospital compared with 26% of those without such brain activity. 

A year later, patients who were discharged were followed up to assess their ability to function independently. Of the patients with brain activity 44% were able to function independently for up to 8 hours a day compared with 14% of those with such signals. Approximately one-third of patients in each group died. 

The researchers found that hidden consciousness was more common in patients with brain injuries from hemorrhage and trauma than from oxygen deprivation. However, the results lack statistical power to determine the predictive value of the EEG analysis across different causes of brain injury.

“Though our study was small, it suggests that EEG – a tool that’s readily available at the patient’s bedside in the intensive care unit in almost any hospital across the globe – has the potential to completely change how we manage patients with acute brain injury,” commented lead author Jan Claassen (Columbia University; NY, USA).

Studies with a larger sample size are required to determine the utility of EEG monitoring in predicting patient outcomes. Furthermore, Claassen comments on how artifacts can be misinterpreted as brain activation if testing paradigm is poorly designed or computational analysis is applied incorrectly.

If the researcher’s findings can be confirmed in a larger study and the technical challenges avoided, this would suggest a strong potential of EEG being used to help physicians predict which patients are most likely to recover. 

Sources: Claassen J, Doyle K, Matory A et al. Detection of brain activation in unresponsive patients with acute brain injury. N. Engl. J. Med. doi:10.1056/NEJMoa1812757 (2019) (Epub ahead of print);

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