• Matthias Kreuzer, Matthew A Stern, Darren Hight, Sebastian Berger, Gerhard Schneider, James W Sleigh, and Paul S García.
• 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.) 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.) the Department of Anesthesiology, Columbia University Irving Medical Center, New York, New York (P.S.G.).
• Anesthesiology. 2020 May 1; 132 (5): 100310161003-1016.

BackgroundPreexisting 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.MethodsThe 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).ResultsThe 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]).ConclusionsLike 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.

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