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

Abstract

Background: 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.

Methods: 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.

Results: 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).

Conclusion: 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.