NIRS frequency analysis to evaluate cerebrovascular reactivity after acute brain injury

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.

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.

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).

Patients with favorable outcomes exhibited increased VLFO during mild hyperoxia with a fraction of inspired oxygen ( ${\mathrm{FiO}}_2$ ) of 50%, whereas no further rise occurred at ${\mathrm{FiO}}_2$ 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.

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.