Covert Consciousness and Traumatic Brain Injury Prognostication: The Acute Care Perspective

Traumatic brain injury (TBI) remains a major cause of death and disability in the United States and beyond. Loss of consciousness is common after TBI but is usually transient. Assessment of level of consciousness is of paramount clinical relevance in the acute setting after TBI, as it influences important decisions about approaches to care and is a key factor in determining prognosis. The bedside neurologic examination is currently the gold standard for consciousness assessment in acute TBI. While this provides a window into the extent of brain injury, it relies on the capability of a patient to demonstrate overt clinical responses that are identified by the examiner. Reliance on overt behaviors to determine level of consciousness is problematic because a variety of factors (e.g., sedation, intoxication, polytrauma) may confound the assessment, leading to misdiagnosing a conscious patient as being unconscious. The term covert consciousness refers to a state of awareness not detectable using traditional bedside neurobehavioral tests but that is detectable via task-based functional magnetic resonance imaging (fMRI) or electroencephalography (EEG). In this narrative review, we will describe techniques to detect both overt and covert consciousness after TBI. In particular, we will address use of the behavioral exam, EEG, fMRI, and other tools to identify consciousness and/or predict its recovery after severe TBI starting in the acute setting.