• Andreas Ranft, Daniel Golkowski, Tobias Kiel, Valentin Riedl, Philipp Kohl, Guido Rohrer, Joachim Pientka, Sebastian Berger, Alexander Thul, Max Maurer, Christine Preibisch, Claus Zimmer, George A Mashour, Eberhard F Kochs, Denis Jordan, and Rüdiger Ilg.
• From the Departments of Neurology (D.G., G.R., A.T., M.M., R.I.), Anesthesiology (A.R., T.K., P.K., J.P., S.B., A.T., M.M., E.F.K., D.J.), and Neuroradiology (V.R., C.P., C.Z.), Klinikum rechts der Isar der Technischen Universität München, München, Germany; and Department of Anesthesiology, University of Michigan Medical School, Ann Arbor, Michigan (G.A.M.).
• Anesthesiology. 2016 Nov 1; 125 (5): 861-872.

BackgroundThe neural correlates of anesthetic-induced unconsciousness have yet to be fully elucidated. Sedative and anesthetic states induced by propofol have been studied extensively, consistently revealing a decrease of frontoparietal and thalamocortical connectivity. There is, however, less understanding of the effects of halogenated ethers on functional brain networks.MethodsThe authors recorded simultaneous resting-state functional magnetic resonance imaging and electroencephalography in 16 artificially ventilated volunteers during sevoflurane anesthesia at burst suppression and 3 and 2 vol% steady-state concentrations for 700 s each to assess functional connectivity changes compared to wakefulness. Electroencephalographic data were analyzed using symbolic transfer entropy (surrogate of information transfer) and permutation entropy (surrogate of cortical information processing). Functional magnetic resonance imaging data were analyzed by an independent component analysis and a region-of-interest-based analysis.ResultsElectroencephalographic analysis showed a significant reduction of anterior-to-posterior symbolic transfer entropy and global permutation entropy. At 2 vol% sevoflurane concentrations, frontal and thalamic networks identified by independent component analysis showed significantly reduced within-network connectivity. Primary sensory networks did not show a significant change. At burst suppression, all cortical networks showed significantly reduced functional connectivity. Region-of-interest-based thalamic connectivity at 2 vol% was significantly reduced to frontoparietal and posterior cingulate cortices but not to sensory areas.ConclusionsSevoflurane decreased frontal and thalamocortical connectivity. The changes in blood oxygenation level dependent connectivity were consistent with reduced anterior-to-posterior directed connectivity and reduced cortical information processing. These data advance the understanding of sevoflurane-induced unconsciousness and contribute to a neural basis of electroencephalographic measures that hold promise for intraoperative anesthesia monitoring.

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