Journal
BRITISH JOURNAL OF ANAESTHESIA
Volume 109, Issue 5, Pages 782-789Publisher
OXFORD UNIV PRESS
DOI: 10.1093/bja/aes265
Keywords
anaesthesia; depth; anaesthetics volatile; isoflurane; monitoring; depth of anaesthesia; monitoring; electroencephalography; rat
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Funding
- Department of Computer Science and Engineering, University of Oulu, Oulu, Finland
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA
- American Heart Association [09SDG2110140]
- National Institute of Health [RO1 HL071568]
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Animal studies often require reliable measures for anaesthetic drug effects. Lately, EEG-based depth of anaesthesia estimation has been widely applied to rat models. This study investigated the reliability of different EEG spectral properties in revealing awakening from isoflurane anaesthesia in rats. Adult Wistar rats with previously implanted frontal epidural electrodes were anaesthetized using isoflurane. The anaesthesia was slowly lightened until awakening, as observed by the first spontaneous movement, after which anaesthesia was induced again by increasing the isoflurane concentration. EEG was recorded during the recovery and induction periods, and the spectrograms and 23 quantitative spectral parameters used in the depth of anaesthesia estimation were calculated from the signals. The awakening was accompanied by a decrease in EEG activity at frequencies below 25 Hz, while the activity at higher frequencies (25150 Hz) was increased. Whereas the behaviour of parameters used to measure activity in the lower frequencies was subject to variability between animals, the increase in higher frequency activity was more consistent, resulting in a statistically significant change in the relative gamma power parameters at the moment of awakening. The increase in frontal relative gamma activity, especially in the 50150 Hz frequency band, seems to be the most reliable EEG indicator for the awakening of a rat from isoflurane anaesthesia. A number of other spectral measures can also be used to detect this event. However, the role of gamma frequencies in the performance of these parameters is crucial.
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