Alpha-delta ratio as a robust marker of the impact of cerebral blood flow on EEG signal during general anesthesia

This study investigated the impact of cerebral blood flow (CBF) on electroencephalography (EEG) during general anesthesia (GA) in neuroradiology procedures and described the pressure-flow relationship during increasing and decreasing mean arterial pressure changes (mAP) challenges. Data were collected from 63 patients (aged 45 [32-53] years, 73 % women) who had EEG, mAP, and CBF monitored during stabilized GA. CBF was approximated by the mean blood velocity in the mean cerebral artery (MCAv mean ), measured by transcranial Doppler. We analyzed the alpha-delta ratio (ADR) to validate that the EEG signal under general anesthesia is influenced by CBF by demonstrating a significant association between MCAv mean changes caused by an mAP challenge and intraoperative EEG parameters. Secondary objectives include (1) an evaluation of response delays between CBF and ADR correlation; (2) characterizing the relationship between CBFv and mAP by comparing linear regression coefficients between increasing and decreasing mAP challenges. mAP challenges lasted for a median duration of 410[220-585] seconds. We found a significant linear relationship between MCAv mean changes and alpha-delta ratio, with the strongest association found for a time delay between 4’ and 9’30 s (permutation test). Our results show directional sensitivity of the cerebral pressure-flow relationship, with asymmetric responses to positive and negative mAP challenges across the cohort (0.28 [0.12 -0.37] and 0.38 [0.25 -0.74] respectively, p = 0.004). The ADR appears to be a delayed marker for studying the relationship between CBF and intraoperative EEG. We observed asymmetry in the cerebral pressure-flow relationship during increasing and decreasing mAP challenges.