Exploratory comparison of autoregulation indices in severe neurological injury using near-infrared spectroscopy and pressure reactivity index

• TOx is calculated from non-invasive NIRS-derived Hgb oxygen saturation and MAP • TOx and PRx smoothed trajectories in patients with brain injury and coma were evaluated • TOx and PRx trajectories showed a good association with median correlation 0.73 • In a heterogenous population, TOx had the best predicted poor outcome with MCC 0.71 • TOx may equal PRx when measuring cerebral autoregulation in brain-injured patients • CA=cerebral autoregulation, TOx=tissue oxygen reactivity index, PRx=pressure reactivity index, NIRS=near infrared spectroscopy, Hgb=hemoglobin, MAP=mean arterial pressure, MCC=Matthew Correlation Coefficient Cerebral autoregulation monitoring utilizes pressure reactivity index (PRx) but has limited use due to its reliance on invasive continuous intracranial pressure monitoring. Non-invasive forms of cerebral autoregulation monitoring may help evaluate secondary neurological injury. We compared temporal trends for tissue oxygen reactivity index (TOx)—a non-invasive cerebral autoregulation index that utilizes the moving correlation coefficient between tissue oxygen saturation and mean arterial pressure—and PRx. A single-center, retrospective exploratory feasibility study in a Level-One Trauma and Tertiary Stroke center comparing PRx and TOx smoothed trajectories in patients with severe neurological injury and comatose exams. Eighteen patients who received TOx and PRx monitoring were analyzed. Individualized smoothed trajectories for TOx and PRx were created. Overall median correlations between TOx and PRx was 0.73. TOx and PRx were also analyzed for their association with poor clinical outcome. Matthew Correlation Coefficient (MCC) suggested that TOx had the strongest association with outcome, reaching a peak value of 0.71 that occurred after day 13 of monitoring. PRx achieved a peak MCC of 0.6 that was consistently reached after day 15 of monitoring. Our findings suggest that TOx may correlate with PRx trajectories. In our cohort, TOx was more strongly associated with poor outcome than PRx. These preliminary results should be interpreted as exploratory, and further research is required to confirm and validate these findings.