NIRS frequency analysis to evaluate cerebrovascular reactivity after acute brain injury

Significance: Cerebral autoregulation (CA) relies on cerebrovascular reactivity, and it is often impaired after acute brain injury (ABI), contributing to secondary brain damage. Noninvasive neuromonitoring with near-infrared spectroscopy (NIRS) can detect oscillations in cerebral hemodynamics, which may reflect autoregulatory function and may therefore be a candidate biomarker for CA monitoring. Aim: We investigated whether changes in the spectral composition of the NIRS signal in ABI under the condition of mild hyperoxia are associated with clinical outcomes in ABI patients. Approach: Bilateral prefrontal NIRS recording was performed during hyperoxia challenges in mechanically ventilated ABI patients admitted to the neurocritical care unit. Spectral power in low-frequency and very low-frequency oscillations (VLFO) was computed and correlated with clinical scores and functional outcomes (Glasgow Outcome Scale). Results: Patients with favorable outcomes exhibited increased VLFO during mild hyperoxia with a fraction of inspired oxygen ( ) of 50%, whereas no further rise occurred at 70%, likely due to oxygen-induced vasoconstriction. In a subgroup of patients with subarachnoid hemorrhage, VLFO changes correlated with clinical severity and independently predicted outcome. Conclusions: Our preliminary findings in a group of 20 patients suggest a potential role of NIRS in the development of individualized neuromonitoring strategies for brain-injured patients.