Monitoring anesthesia using simultaneous functional Near Infrared Spectroscopy and Electroencephalography

•The anesthesia maintenance phase is characterized by a significant decrease in the complexity and power of cerebral hemodynamic signals.•Adults exhibit a higher coupling between low frequency oscillations (0.01–0.1 Hz) in fNIRS and EEG as compared to children.•fNIRS offers a complementary neurovascular assessment to EEG that improves the accuracy of anesthesia monitoring. This study aims to understand the neural and hemodynamic responses during general anesthesia in order to develop a comprehensive multimodal anesthesia depth monitor using simultaneous functional Near Infrared Spectroscopy (fNIRS) and Electroencephalogram (EEG). 37 adults and 17 children were monitored with simultaneous fNIRS and EEG, during the complete general anesthesia process. The coupling of fNIRS signals with neuronal signals (EEG) was calculated. Measures of complexity (sample entropy) and phase difference were also quantified from fNIRS signals to identify unique fNIRS based biomarkers of general anesthesia. A significant decrease in the complexity and power of fNIRS signals characterize the anesthesia maintenance phase. Furthermore, responses to anesthesia vary between adults and children in terms of neurovascular coupling and frontal EEG alpha power. This study shows that fNIRS signals could reliably quantify the underlying neuronal activity under general anesthesia and clearly distinguish the different phases throughout the procedure in adults and children (with less accuracy). A multimodal approach incorporating the specific differences between age groups, provides a reliable measure of anesthesia depth.