Visualization of Cerebral Pressure Autoregulatory Insults in Traumatic Brain Injury

OBJECTIVES: The first aim was to investigate the combined effect of insult intensity and duration of the pressure reactivity index (PRx) and deviation from the autoregulatory cerebral perfusion pressure target (triangle CPPopt = actual CPP - optimal CPP [CPPopt]) on outcome in traumatic brain injury. The second aim was to determine if PRx influenced the association between intracranial pressure (ICP), CPP, and triangle CPPopt with outcome. DESIGN: Observational cohort study. SETTING: Neurocritical care unit, Cambridge, United Kingdom. PATIENTS: Five hundred fifty-three traumatic brain injury patients with ICP and arterial blood pressure monitoring and 6-month outcome data (Glasgow Outcome Scale [GOS]). INTERVENTION: None. MEASUREMENTS AND MAIN RESULTS: The insult intensity (mm Hg or PRx coefficient) and duration (minutes) of ICP, PRx, CPP, and triangle CPPopt were correlated with GOS and visualized in heatmaps. In these plots, there was a transition from favorable to unfavorable outcome when PRx remained positive for 30 minutes and this was also the case for shorter durations when the intensity was higher. In a similar plot of triangle CPPopt, there was a gradual transition from favorable to unfavorable outcome when triangle CPPopt went below -5 mm Hg for 30-minute episodes of time and for shorter durations for more negative triangle CPPopt. Furthermore, the percentage of monitoring time with certain combinations of PRx with ICP, CPP, and triangle CPPopt were correlated with GOS and visualized in heatmaps. In the combined PRx/ICP heatmap, ICP above 20 mm Hg together with PRx above 0 correlated with unfavorable outcome. In a PRx/CPP heatmap, CPP below 70 mm Hg together with PRx above 0.2-0.4 correlated with unfavorable outcome. In the PRx-/triangle CPPopt heatmap, triangle CPPopt below 0 together with PRx above 0.2-0.4 correlated with unfavorable outcome. CONCLUSIONS: Higher intensities for longer durations of positive PRx and negative triangle CPPopt correlated with worse outcome. Elevated ICP, low CPP, and negative triangle CPPopt were particularly associated with worse outcomes when the cerebral pressure autoregulation was concurrently impaired.