Background: Although older traumatic brain injury (TBI) patients often exhibit cerebral autoregulatory impairment with high pressure reactivity index (PRx), the role of autoregulatory-guided management in these patients remains elusive. In this study, we aimed to explore if age affected the prognostic role of the autoregulatory variables, PRx and the PRx-derived optimal cerebral perfusion pressure (CPPopt), in a large TBI cohort.

Methods: In this observational study, 550 TBI patients who had been treated in the neurocritical care unit, Addenbrooke's Hospital, Cambridge, UK, between 2002 and 2022 with available data on age, intracranial pressure monitoring, and outcome (Glasgow Outcome Scale [GOS]) were included. The patients were classified into three age groups; youth and early adulthood (16-39 years), middle adulthood (40-59 years), and senior adulthood (60 years and above). Autoregulatory variables were studied in relation to outcome using heatmaps. Multivariate logistic regressions of mortality and favourable outcome (GOS 4 to 5) were performed with PRx and Delta CPPopt (CPP-CPPopt) in addition to baseline variables.

Results: TBI patients in the senior adulthood group exhibited higher PRx and lower ICP than younger patients. There was a transition towards worse outcome with higher PRx in heatmaps for all age groups. The combination of high PRx together with low CPP or negative Delta CPPopt was particularly associated with lower GOS. In multivariate logistic regressions, higher PRx remained independently associated with higher mortality and lower rate of favourable outcome in the senior adulthood cohort. There was a transition towards worse outcome for negative Delta CPPopt for all age groups, but it did not reach statistical significance for the senior adulthood group.

Conclusions: PRx was found to be an independent outcome predictor and influenced the safe and dangerous CPP and Delta CPPopt interval for all age groups. Thus, TBI patients older than 60 years may also benefit from autoregulatory-guided management and should not necessarily be excluded from future trials on such therapeutic strategies.