Further Controversies About Brain Tissue Oxygenation Pressure-Reactivity After Traumatic Brain Injury

Andresen M, Donnelly J, Aries M, Juhler M, Menon D, Hutchinson P & Smielewski P

This paper investigates the potential usefulness of the Brain Tissue Oxygenation Pressure-Reactivity (ORx) index in a large cohort of patients treated at Addenbrooke’s Hospital in Cambridge, England. The work was carried out during Morten Andresen’s stay at the institution in 2014.


Continuous monitoring of cerebral autoregulation is considered clinically useful due to its ability to warn against brain ischemic insults, which may translate to a relationship with adverse outcome. It is typically performed using the pressure reactivity index (PRx) based on mean arterial pressure and intracranial pressure. A new ORx index based on brain tissue oxygenation and cerebral perfusion pressure (CPP) has been proposed that similarly allows for evaluation of cerebrovascular reactivity. Conflicting results exist concerning its clinical utility.


Retrospective analysis was performed in 85 patients with traumatic brain injury (TBI). ORx was calculated using three time windows of 5, 20, and 60 min. Correlation coefficients and individual “optimal CPP” (CPPopt) were calculated using both PRx and ORx, and relation to patient outcome investigated.


Correlation coefficients for all comparisons between PRx and ORx indicated poor association between these indices (range from –0.04 to 0.07). PRx was significantly lower in patients with good outcome (p = 0.01), while none of the ORx indices proved to be significantly different in the two outcome groups. Higher mortality related to average CPP < CPPopt was found regardless of which index was used to calculate CPPopt.


In the TBI setting, ORx does not appear to correlate with vascular pressure reactivity as assessed with PRx. Its potential use for individualizing CPP thresholds remains unclear.

Read the full paper in Neurocrit Care (click here).