Temporal Neurophysiological Dynamics in Traumatic Brain Injury: Role of Pressure Reactivity and Optimal Cerebral Perfusion Pressure for Predicting Outcome

Abstract

Intracranial pressure (ICP), cerebral perfusion pressure (CPP), and the pressure reactivity index (PRx) have been shown to correlate with outcome after traumatic brain injury (TBI), but their temporal evolution is less studied. Optimal CPP (CPPopt; i.e., the CPP with the lowest [optimal] PRx value) has been proposed as a dynamic, individualized CPP target. Our aim was to map the temporal course of these parameters and their relation to outcome, in particular the extent and impact of CPP insults based both on fixed CPP thresholds and on divergence from CPPopt. Data from 362 TBI patients with ICP-monitoring treated at the neurointensive care unit of Uppsala University Hospital, Uppsala, Sweden, between 2008-2016 were retrospectively analyzed for the temporal course of ICP, mean arterial blood pressure, CPP, PRx, PRx55-15 (a variant of PRx), and CPPopt the first 10 days post-injury. PRx and PRx55-15 showed significantly lower/better values for those with favorable outcome, most pronounced on Days 2 to 5. PRx55-15 gave better separation between the two groups. In the univariate analysis, CPP insults (both fixed and CPPopt-thresholds) were significantly correlated with outcome on these days. Multi-variate logistic regression showed that age, Glasgow Coma Score Motor, pupillary abnormality at admission, CPP > CPPopt, and PRx55-15 were significant independent outcome predictors. PRx was significant when PRx55-15 was excluded. High PRx55-15 and high grade of monitoring time with CPP > CPPopt, but not the traditional fixed CPP thresholds, were strong predictors for worse clinical outcome. The study supports the concept that CPPopt is an important parameter in TBI management.

Keywords: CPPopt; cerebral autoregulation; neurointensive care; traumatic brain injury.