Photo Credit: EvgeniyShkolenko

The following is a summary of “Revisiting the oxygen reactivity index in traumatic brain injury: the complementary value of combined focal and global autoregulation monitoring,” published in the January 2025 issue of Critical Care by Wettervik et al. 

The oxygen reactivity index (ORx) was used to describe the correlation between focal brain tissue oxygen (pbtO₂) levels and cerebral perfusion pressure (CPP).  

Researchers conducted a retrospective study investigating whether the ORx conveys cerebral autoregulatory information and its relationship to outcomes in a larger traumatic brain injury (TBI) cohort.  

They included 425 patients with TBI treated at Addenbrooke’s Hospital, Cambridge, UK, who underwent intracranial pressure (ICP) and pbtO₂ monitoring for at least 12 hours. The association between the ORx and ICP, pressure reactivity index (PRx), CPP, ΔCPPopt (actual CPP-CPPopt [PRx-based optimal CPP]), and pbtO₂ was assessed using generalized additive models (GAMs). Logistic regression and heatmaps were used to examine the relationship between ORx and outcome (Glasgow Outcome Scale [GOS]) for 239 patients with available GOS data.  

The results showed the ORx increased with higher ICP, PRx above +0.30, CPP below 60-70 mmHg, and negative ΔCPPopt. Unlike PRx, ORx did not rise with higher CPP. Heatmaps indicated a shift towards worse outcomes when ORx exceeded +0.50, especially for prolonged durations, and when combined with high ICP, high PRx, low CPP, negative ΔCPPopt, and low pbtO₂. Multivariable logistic regressions revealed that higher ORx was linked to increased mortality. 

Investigators concluded that ORx appeared sensitive to the lower, but not the upper, limit of autoregulation, unlike PRx, and the combination of high ORx and PRx values was linked to worse outcomes, suggesting that ORx could complement PRx and help identify safe and dangerous perfusion target intervals. 

Source: ccforum.biomedcentral.com/articles/10.1186/s13054-025-05261-6