Brain Tissue Oxygen and Cerebrovascular Reactivity in Traumatic Brain Injury: A Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury Exploratory Analysis of Insult Burden

Pressure reactivity index (PRx) and brain tissue oxygen (PbtO(2)) are associated with outcome in traumatic brain injury (TBI). This study explores the relationship between PRx and PbtO(2) in adult moderate/severe TBI. Using the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI) high resolution intensive care unit (ICU) sub-study cohort, we evaluated those patients with archived high-frequency digital intraparenchymal intracranial pressure (ICP) and PbtO(2) monitoring data of, a minimum of 6 h in duration, and the presence of a 6 month Glasgow Outcome Scale -Extended (GOSE) score. Digital physiological signals were processed for ICP, PbtO(2), and PRx, with the % time above/below defined thresholds determined. The duration of ICP, PbtO(2), and PRx derangements was characterized. Associations with dichotomized 6-month GOSE (alive/dead, and favorable/unfavorable outcome; <= 4 = unfavorable), were assessed. A total of 43 patients were included. Severely impaired cerebrovascular reactivity was seen during elevated ICP and low PbtO(2) episodes. However, most of the acute ICU physiological derangements were impaired cerebrovascular reactivity, not ICP elevations or low PbtO(2) episodes. Low PbtO(2) without PRx impairment was rarely seen. % time spent above PRx threshold was associated with mortality at 6 months for thresholds of 0 (area under the curve [AUC] 0.734, p = 0.003), > +0.25 (AUC 0.747, p = 0.002) and > +0.35 (AUC 0.745, p = 0.002). Similar relationships were not seen for % time with ICP >20 mm Hg, and PbtO(2) < 20 mm Hg in this cohort. Extreme impairment in cerebrovascular reactivity is seen during concurrent episodes of elevated ICP and low PbtO(2). However, the majority of the deranged cerebral physiology seen during the acute ICU phase is impairment in cerebrovascular reactivity, with most impairment occurring in the presence of normal PbtO(2) levels. Measures of cerebrovascular reactivity appear to display the most consistent associations with global outcome in TBI, compared with ICP and PbtO(2).