Anesth Analg 2006;102:966
© 2006 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000190854.30550.01
LETTER TO THE EDITOR
EEG During Anesthesia Is Not a Linear Random Process
Satoshi Hagihira, MD, PhD,
Masaki Takashina, MD,
Takahiko Mori, MD, and
Takashi Mashimo, MD, PhD
Department of Anesthesiology, Osaka University Graduate School of Medicine, hagihira{at}masui.med.osaka-u.ac.jp (Hagihira)
Surgical Center, Osaka University Hospital (Takashina)
Department of Anesthesiology, Osaka General Medical Center (Mori)
Department of Anesthesiology, Osaka University Graduate School of Medicine, Osaka, Japan (Mashimo)
To the Editor:
We read the recent article written by Jeleazcov et al. (1) with great interest. They analyzed 90 h of electroencephalogram (EEG) recorded from 20 patients. They found that the bicoherence was zero or a mere constant. We found a significant increase of EEG bicoherence during isoflurane or sevoflurane anesthesia (2–4). We also found the same changes in EEG bicoherence during propofol-fentanyl anesthesia (data not shown). What is the difference? Bispectral analysis quantifies the phase relation (quadratic phase coupling) among the frequency components of a signal in stationary state. This means that all epochs used for calculation of bispectrum/bicoherence must be taken from a signal in the same stationary state, whereas Jeleazcov et al. (1) calculated EEG bicoherence from EEG data recorded from different patients in various anesthetic states, which is theoretically violent. We could not get correct EEG bicoherence values with such a method. We should analyze the EEG recorded at one anesthetic state of one patient. Although we could occasionally obtain meaningful EEG bicoherence data from EEG in transient state (2), they were probably exceptional cases. We think that EEG during anesthesia cannot be a linear random process.
References
- Jeleazcov C, Fechner J, Schwilden H. Electroencephalogram monitoring during anesthesia with propofol and alfentanil: the impact of second order spectral analysis. Anesth Analg 2005;100:1365–9.[Abstract/Free Full Text]
- Hagihira S, Takashina M, Mori T, et al. Practical issues in bispectral analysis of electroencephalographic signals. Anesth Analg 2001;93:966–70.[Abstract/Free Full Text]
- Hagihira S, Takashina M, Mori T, et al. Changes of electroencephalographic bicoherence during isoflurane anesthesia combined with epidural anesthesia. Anesthesiology 2002;97:1409–15.[ISI][Medline]
- Hagihira S, Takashina M, Ueyama H, et al. Electroencephalographic bicoherence is sensitive to noxious stimuli during isoflurane or sevoflurane anesthesia. Anesthesiology 2004;100:818–25.[ISI][Medline]
