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


METHODS
The effects of sub-anesthetic (159 (21); mean (SD) ng/ml) and anesthetic (1,959 (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.


RESULTS
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.


CONCLUSIONS
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.


CONCLUSIONS
The entropy monitor is not adequate for monitoring S-ketamine-induced hypnosis.
Maksimow
A
A
Turku PET Centre, University of Turku, P.O. Box 52, FIN-20521 Turku, Finland. anu.maksimow@utu.fi
Särkelä
M
M
Långsjö
J W
JW
Salmi
E
E
Kaisti
K K
KK
Yli-Hankala
A
A
Hinkka-Yli-Salomäki
S
S
Scheinin
H
H
Jääskeläinen
S K
SK
D000328:Adult; D000778:Anesthetics, Dissociative / Q000494:pharmacology*; D018686:Anesthetics, Intravenous / Q000494:pharmacology; D001921:Brain / Q000187:drug effects; D004569:Electroencephalography / Q000187:drug effects*; D004576:Electromyography / Q000187:drug effects; D006801:Humans; D007649:Ketamine / Q000494:pharmacology*; D008297:Male; D016343:Monitoring, Intraoperative / Q000379:methods*; D015742:Propofol / Q000494:pharmacology; D012680:Sensitivity and Specificity
D000778:Anesthetics, Dissociative; D018686:Anesthetics, Intravenous; D007649:Ketamine; D015742:Propofol