Functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) may detect consciousness in ICU patients with severe traumatic brain injuries when a standard bedside neurological exam comes up short, according to new research at Massachusetts General Hospital (MGH).
Studies have suggested that up to 40 percent of patients who have been deemed unconscious may actually be conscious on some level.
While prior research has used fMRI or EEG to detect this sort of “covert consciousness” in patients who have moved from acute-care hospitals to rehabilitation or nursing care facilities, no such study has been conducted in ICU patients.
In fact, the study is the first to test such an approach in acutely ill patients for whom critical decisions may need to be made regarding the continuation of life-sustaining care.
“Early detection of consciousness and brain function in the intensive care unit could allow families to make more informed decisions about the care of loved ones,” said Brian Edlow, M.D., of the Center for Neurotechnology and Neurorecovery in the MGH Department of Neurology, co-lead and corresponding author of the study.
“Also, since early recovery of consciousness is associated with better long-term outcomes, these tests could help patients gain access to rehabilitative care once they are discharged from an ICU.”
For ICU patients with serious brain injuries, the standard bedside neurological examination may inaccurately identify a patient as unconscious for several reasons: the patient may be unable to speak, write or move because of the effects of the injury itself or sedating medications or a clinician may mistake a weak but intentional movement as a reflex response.
For the study, the researchers enrolled 16 patients being cared for in MGH intensive care units after severe traumatic brain injury. Upon enrollment, eight were able to respond to language, three were classified as minimally conscious without language response, three classified as vegetative and two as in a coma.
fMRI studies were conducted as soon as patients were stable enough for the procedure, and EEG readings were taken soon afterwards, ideally but not always within 24 hours. A group of 16 healthy age- and sex-matched volunteers underwent the same procedures as a control group.
The screenings were taken under three experimental conditions. To test for a mismatch between the patients’ ability to imagine performing a task and their ability to physically express themselves — what is called cognitive motor dissociation — patients were asked to imagine squeezing and releasing their right hand while in the fMRI scanner and while EEG readings were being taken.
Since it is known that certain parts of the brain can react to sounds even when a person is sleeping or under sedation, the patients were exposed to brief recordings of spoken language and of music during both the fMRI and EEG tests.
These screenings were developed to detect activity in areas of the brain that are part of the higher-order cortex, which interprets the simple signals processed by the primary cortex — in this instance not just detecting a sound but potentially recognizing what it is.
Of eight patients who had been classified as unable to respond to language during the traditional bedside examination, the researchers found evidence in four patients of covert consciousness based on the hand-squeeze exercise, including the three originally classified as vegetative.
In two other patients, higher-order cortex activity was seen in response to either language or music. Although higher-order cortical activity doesn’t necessarily prove that a patient is conscious, Edlow notes, a response in these brain structures could have implications for a patient’s future recovery.
Edlow also notes that negative responses to these tests should not be considered a poor likelihood of recovery. For example, about 25 percent of the healthy controls had no detectable brain response during the hand squeeze imagery test, and one of the comatose patients who showed no response to language, music or motor imagery during the early fMRI and EEG tests made a complete recovery six months later.
In fact, no links were shown between early brain responses and long-term outcomes, which could be due to the small size of the study or the fact that several patients were sedated during the fMRI and EEG tests.
The findings are published in the journal Brain.
Source: Massachusetts General Hospital