Increase in high frequency EEG activity explains the poor performance of EEG spectral entropy monitor during S-ketamine anesthesia

• Published in: Clinical neurophysiology Vol. 117; no. 8; pp. 1660 - 1668
• Main Authors: Maksimow, A., Särkelä, M., Långsjö, J.W., Salmi, E., Kaisti, K.K., Yli-Hankala, A., Hinkka-Yli-Salomäki, S., Scheinin, H., Jääskeläinen, S.K.
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 01.08.2006; Elsevier Science
• Subjects: Adult; Anesthetics, Dissociative - pharmacology; Anesthetics, Intravenous - pharmacology; Anesthetics. Neuromuscular blocking agents; Biological and medical sciences; Brain - drug effects; Depth of anesthesia; EEG; Electrodiagnosis. Electric activity recording; Electroencephalography - drug effects; Electromyography - drug effects; Humans; Investigative techniques, diagnostic techniques (general aspects); Ketamine - pharmacology; Male; Medical sciences; Monitoring; Monitoring, Intraoperative - methods; Nervous system; Neuropharmacology; Pharmacology. Drug treatments; Propofol - pharmacology; S-Ketamine; Sensitivity and Specificity; Spectral entropy; Spectral entropy; S-Ketamine; EEG; Monitoring; Depth of anesthesia; Human; EEC; Electrophysiology; Electroencephalography; Entropy; Spectral analysis; Depth; Ketamine; Anesthetic; Anesthesia; Serum; Hypnosis; High frequency; Performance; Power spectrum
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/j.clinph.2006.05.011

To study the effects of S-ketamine on the EEG and to investigate whether spectral entropy of the EEG can be used to assess the depth of hypnosis during S-ketamine anesthesia. The effects of sub-anesthetic (159 (21); mean (SD) ng/ml) and anesthetic (1959 (442) ng/ml) serum concentrations of S-ketamine on state entropy (SE), response entropy (RE) and classical EEG spectral power variables (recorded using the Entropy™ Module, GE Healthcare, Helsinki, Finland) were studied in 8 healthy males. These EEG data were compared with EEG recordings from 6 matching subjects anesthetized with propofol. The entropy values decreased from the baseline SE 85 (3) and RE 96 (3) to SE 55 (18) and RE 72 (17) during S-ketamine anesthesia but both inter- and intra-individual variation of entropy indices was wide and their specificity to indicate unconsciousness was poor. Propofol induced more pronounced increase in delta power ( P<0.02) than S-ketamine, whereas anesthetic S-ketamine induced more high frequency EEG activity in the gamma band ( P<0.001). Relative power of 20–70 Hz EEG activity was associated with high SE ( P=0.02) and RE ( P=0.03) values during S-ketamine anesthesia. These differences in low and high frequency EEG power bands probably explain why entropy monitor, while adequate for propofol, is not suitable for assessing the depth of S-ketamine anesthesia. The entropy monitor is not adequate for monitoring S-ketamine-induced hypnosis.