• Carla Troyas, Julian Ostertag, Gerhard Schneider, Paul S Garcia, Jamie W Sleigh, and Matthias Kreuzer.
• Department of Anesthesiology and Intensive Care Medicine, Technical University of Munich, School of Medicine, Munich, Germany.
• Anesthesiology. 2024 Sep 23.

BackgroundNumerous, sometimes conflicting, changes in brain functional connectivity have been associated with the transition from wakefulness to unresponsiveness at induction of general anesthesia. However, relatively few studies have looked at: the detailed time evolution of the transition; for different EEG frequency bands; and in the clinical scenario of surgical patients undergoing general anesthesia.MethodsWe investigated the changes in the frontal and fronto-parietal directed and undirected functional connectivity to multichannel EEG data recorded from 29 adult male surgical patients undergoing propofol-induced loss of consciousness during induction of anesthesia. Directed functional connectivity was estimated using bivariate frequency domain Granger causality, and undirected connectivity was assessed using EEG coherence.ResultsAround the point of loss of consciousness: local frontal, interhemispheric frontal, and frontoparietal feedback and feedforward Granger causality all decreased between 31% and 51.5% in the delta-band (median [interquartile range] for local frontal: 0.14 [0.08, 0.27] to 0.08 [0.06, 0.12] (p=0.02)). After a lag of a few minutes, Granger Causality markedly increased in the gamma and beta bands for local frontal (0.03 [0.02, 0.07] to 0.09 [0.07, 0.11](p<0.001)) and long-distance cross-hemispheric frontoparietal feedback (0.02 [0.01, 0.04] to 0.07 [0.04, 0.09], p<0.001) and feedforward (0.02 [0.01, 0.04] to 0.03 [0.03, 0.04], p=0.01) coupling; but not for within-hemispheric frontoparietal feedback and feedforward. Frontal interhemispheric EEG coherence significantly decreased in the lower frequencies (f<12Hz) at loss of consciousness, while no significant increase for the beta and gamma bands was observed.ConclusionsPropofol-induced loss of consciousness in surgical patients is associated with a global breakdown in low-frequency directed functional connectivity, coupled with a high-frequency increase between closely located brain regions. At loss of consciousness, Granger causality shows more pronounced changes than coherence.Copyright © 2024 American Society of Anesthesiologists. All Rights Reserved.

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