An updated introduction to electroencephalogram-based brain monitoring during intended general anesthesia
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CONTINUING PROFESSIONAL DEVELOPMENT
Continuing professional development module An updated introduction to electroencephalogram-based brain monitoring during intended general anesthesia
Darren F. Hight, PhD • Heiko A. Kaiser, MD • Jamie W. Sleigh, MBChB • Michael S. Avidan, MBBCh
Received: 3 March 2019 / Revised: 25 July 2019 / Accepted: 13 July 2020 / Published online: 15 November 2020 Ó Canadian Anesthesiologists’ Society 2020, corrected publication 2020
Abstract The electroencephalogram (EEG) provides a reliable reflection of the brain’s electrical state, so it can reassure us that the anesthetic agents are actually reaching the patient’s brain, and are having the desired effect. In most patients, the EEG changes somewhat predictably in response to propofol and volatile agents, so a frontal EEG channel can guide avoidance of insufficient and excessive administration of general anesthesia. Persistent alphaspindles (around 10 Hz) phase-amplitude coupled with slow delta waves (around 1 Hz) are commonly seen during an ‘‘appropriate hypnotic state of general anesthesia’’. Such patterns can be appreciated from the EEG waveform or from the spectrogram (a colour-coded display of how the power in the various EEG frequencies changes with time). Nevertheless, there are exceptions to this. For example, administration of ketamine and nitrous oxide is generally not associated with the aforementioned alphaspindle coupled with delta wave pattern. Also, some patients, including older adults and those with neurodegenerative disorders, are less predisposed to generate a strong electroencephalographic ‘‘alphaspindle’’ pattern during general anesthesia. There might
also be some rare instances when the frontal EEG shows a pattern suggestive of general anesthesia, while the patient has some awareness and is able to follow simple commands, albeit this is typically without obvious distress or memory formation. Thus, the frontal EEG alone, as currently analyzed, is an imperfect but clinically useful mirror, and more scientific insights will be needed before we can claim to have a reliable readout of brain ‘‘function’’ during general anesthesia.
D. F. Hight, PhD H. A. Kaiser, MD Department of Anaesthesiology and Pain Medicine, Bern University Hospital, University of Bern, Bern, Switzerland
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J. W. Sleigh, MBChB Department of Anaesthesiology, University of Auckland, Auckland, New Zealand M. S. Avidan, MBBCh (&) Department of Anesthesiology, Washington University School of Medicine, 660 South Euclid Avenue, Campus Box 8054, St. Louis, MO, USA e-mail: [email protected]
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Objectives of the Continuing Professional Development module: After reading this module, the reader should be able to: 1)
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Formulate basic concepts of the typical electroencephalogram (EEG) changes accompanying general anesthesia with volatile anesthetics or propofol. Differentiate excessive, adequate, and possibly insufficient ‘‘hypnosis’’ during intended general anesthesia, based on the EEG. Apply information gained from the raw EEG or its density spect
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