Perioperative Medicine  |   May 2020
Spectral and Entropic Features Are Altered by Age in the Electroencephalogram in Patients under Sevoflurane Anesthesia
Author Notes
  • From the Department of Anaesthesiology and Intensive Care, Klinikum rechts der Isar, Technical University Munich, Munich, Germany (M.K., S.B., G.S.); the Department of Anesthesiology (M.K., M.A.S., P.S.G.) and the Medical Scientist Training Program (M.A.S.), Emory University School of Medicine, Atlanta, Georgia; the Anesthesiology and Research Divisions, Atlanta Veterans Affairs Medical Center, (M.K., M.A.S., P.S.G.) Atlanta, Georgia; the Department of Anaesthesia, Waikato Clinical School, University of Auckland, Hamilton, New Zealand (D.H., J.W.S.); the Waikato District Health Board, Hamilton, New Zealand (D.H., J.W.S.); the Department of Anaesthesiology and Pain Medicine, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland (D.H.); and the Department of Anesthesiology, Columbia University Irving Medical Center, New York, New York (P.S.G.).
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    Supplemental Digital Content is available for this article. Direct URL citations appear in the printed text and are available in both the HTML and PDF versions of this article. Links to the digital files are provided in the HTML text of this article on the Journal’s Web site (www.anesthesiology.org).×
  • Submitted for publication December 9, 2018. Accepted for publication December 5, 2019. Published online first on February 25, 2020.
    Submitted for publication December 9, 2018. Accepted for publication December 5, 2019. Published online first on February 25, 2020.×
  • Address correspondence to Dr. García: Department of Anesthesiology, Vagelos College of Physicians and Surgeons, Columbia University Irving Medical Center, 622 West 168th Street, New York, New York 10032. pg2618@cumc.columbia.edu. Information on purchasing reprints may be found at www.anesthesiology.org or on the masthead page at the beginning of this issue. Anesthesiology’s articles are made freely accessible to all readers, for personal use only, 6 months from the cover date of the issue.
Article Information
Perioperative Medicine / Clinical Science / Central and Peripheral Nervous Systems / Pharmacology
Perioperative Medicine   |   May 2020
Spectral and Entropic Features Are Altered by Age in the Electroencephalogram in Patients under Sevoflurane Anesthesia
Anesthesiology 5 2020, Vol.132, 1003-1016. doi:https://doi.org/10.1097/ALN.0000000000003182
Anesthesiology 5 2020, Vol.132, 1003-1016. doi:https://doi.org/10.1097/ALN.0000000000003182
Abstract

Background: Preexisting factors such as age and cognitive performance can influence the electroencephalogram (EEG) during general anesthesia. Specifically, spectral EEG power is lower in elderly, compared to younger, subjects. Here, the authors investigate age-related changes in EEG architecture in patients undergoing general anesthesia through a detailed examination of spectral and entropic measures.

Methods: The authors retrospectively studied 180 frontal EEG recordings from patients undergoing general anesthesia, induced with propofol/fentanyl and maintained by sevoflurane at the Waikato Hospital in Hamilton, New Zealand. The authors calculated power spectral density and normalized power spectral density, the entropic measures approximate and permutation entropy, as well as the beta ratio and spectral entropy as exemplary parameters used in current monitoring systems from segments of EEG obtained before the onset of surgery (i.e., with no noxious stimulation).

Results: The oldest quartile of patients had significantly lower 1/f characteristics (P < 0.001; area under the receiver operating characteristics curve, 0.84 [0.76 0.92]), indicative of a more uniform distribution of spectral power. Analysis of the normalized power spectral density revealed no significant impact of age on relative alpha (P = 0.693; area under the receiver operating characteristics curve, 0.52 [0.41 0.63]) and a significant but weak effect on relative beta power (P = 0.041; area under the receiver operating characteristics curve, 0.62 [0.52 0.73]). Using entropic parameters, the authors found a significant age-related change toward a more irregular and unpredictable EEG (permutation entropy: P < 0.001, area under the receiver operating characteristics curve, 0.81 [0.71 0.90]; approximate entropy: P < 0.001; area under the receiver operating characteristics curve, 0.76 [0.66 0.85]). With approximate entropy, the authors could also detect an age-induced change in alpha-band activity (P = 0.002; area under the receiver operating characteristics curve, 0.69 [0.60 78]).

Conclusions: Like the sleep literature, spectral and entropic EEG features under general anesthesia change with age revealing a shift toward a faster, more irregular, oscillatory composition of the EEG in older patients. Age-related changes in neurophysiological activity may underlie these findings however the contribution of age-related changes in filtering properties or the signal to noise ratio must also be considered. Regardless, most current EEG technology used to guide anesthetic management focus on spectral features, and improvements to these devices might involve integration of entropic features of the raw EEG.

Editor’s Perspective:

What We Already Know about This Topic:

  • Age-related changes in the electroencephalograms of anesthetized surgical patients have been explored but not fully characterized

What This Article Tells Us That Is New:

  • Older age is associated with a shift to a less predictable electroencephalogram, which could influence intraoperative monitoring approaches