Improving Diagnosis and Prognosis in Acute Severe Brain Injury
Abstract
Detecting signs of preserved awareness and predicting recovery after severe acute brain injury in the intensive care unit (ICU) is clinically and scientifically challenging. Treatment decisions are often based on unreliable behavioural responses rather than objective and quantifiable measures. This dissertation examines the utility of using advanced neuroimaging methods to improve diagnosis and prognosis after severe brain injury. In Chapter 2, a series of functional MRI (fMRI) studies were employed to assess preserved brain activity in a patient with severe traumatic brain injury (TBI) and at 9-months post injury. Preserved sound and speech perception were demonstrated acutely, and an increased response to higher-order cognitive tasks with greater functional connectivity was observed at recovery. In Chapter 3, we performed a series of multimodal, longitudinal investigations in 33 patients with acute severe TBI that integrated results from resting-state and stimulus-based fMRI, diffusion tractography, and behavioural assessments to identify biomarkers of recovery. Neuroimaging measures predicted good functional recovery at 6 months with 87.5% accuracy and outperformed clinical and demographic predictors. In Chapter 4, we evaluated the use of functional near-infrared spectroscopy (fNIRS) to detect biomarkers of conscious processing. We demonstrate that fNIRS can capture somatosensory perception, auditory processing, and command-driven brain activity with adequate sensitivity at the single-subject level in healthy participants. We then used fNIRS to detect covert brain activity in one acutely brain-injured patient in the ICU and found a greater level of cognitive processing than what bedside behavioural measures demonstrated. In Chapter 5, we test for preserved covert conscious awareness in 14 critically ill unresponsive patients using fNIRS. We found that 4 patients were able to willfully modulate their brain activity when asked to complete a motor imagery task, suggesting a level of awareness that was entirely inconsistent with their behavioural examination. Collectively, these studies demonstrate that advanced neuroimaging techniques can improve the detection of consciousness in the ICU and accurately predict functional recovery. These tests may inform discussions regarding the trajectory of care and drive efforts to develop interventions that facilitate recovery and improve quality of life.