Spectral and Entropic Features Are Altered by Age in the Electroencephalogram in Patients under Sevoflurane Anesthesia

• Authors: Paul Garcia, Emory University; Peter Sebel, Emory University; M Kreuzer, Technical University of Munich; MA Stern, Emory University; D Hight, University of Auckland; S Berger, Technical University of Munich; G Schneider, Technical University of Munich; JW Sleigh, University of Auckland
• Journal Title: ANESTHESIOLOGY
• Volume: Volume 132, Number 5
• Publisher: LIPPINCOTT WILLIAMS & WILKINS | 2020-05-01, Pages 1003-1016
• Type of Work: Article
• Publisher DOI: http://doi.org/10.1097/ALN.0000000000003182
• Keywords: Science & Technology; Life Sciences & Biomedicine; Anesthesiology; APPROXIMATE ENTROPY; PERMUTATION ENTROPY; POSTOPERATIVE DELIRIUM; INDEX CALCULATION; MONITORING DEPTH; CEREBRAL STATE; TIME-DELAY; SLEEP EEG; PROPOFOL; POWER

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. Agerelated 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. (ANESTHESIOLOGY 2020; 132:1003-16).