A combination of electroencephalogram and auditory evoked potentials separates different levels of anesthesia in volunteers.
BACKGROUND
It has been shown that the combination of electroencephalogram (EEG) and auditory evoked potentials (AEP) allows a good separation of consciousness from unconsciousness. In the present study, we sought a combined EEG/AEP indicator that allows both separation of consciousness from unconsciousness and discrimination among different levels of sedation and hypnosis over a wider range of anesthesia.


METHODS
Fifteen unpremedicated volunteers received mono-anesthesia with sevoflurane or propofol in a randomized crossover design in two consecutive sessions. Loss of consciousness (LOC) and EEG burst suppression (BSP) defined end-points from the upper and lower range of general anesthesia. In addition to those two extremes, the difference between anesthetic concentration at BSP and LOC was divided into three equal intervals, resulting in two intermediate levels which divided the concentration from LOC (minimum) to BSP (maximum) into three equal steps. This data set was used to test whether a previously described combined EEG/AEP indicator "detector of consciousness" can also discriminate among degrees of anesthetic effects from the awake state to BSP. Furthermore, a new improved combined EEG/AEP indicator was developed on the basis of the data from the current study, and subsequently this new indicator was tested for its ability to separate consciousness from unconsciousness with the patient data set.


RESULTS
The former "detector of consciousness" showed a prediction probability (P(K)) of 0.77 to separate different levels of anesthesia from the current study, whereas for the new combined EEG/AEP indicator, P(K) was 0.94. The new indicator was further applied to the previous study and achieved a P(K) of 0.89.


CONCLUSIONS
These results show that with the new indicator presented here, a combination of EEG and AEP parameters can be used to differentiate degrees of anesthetic effects over a wide range of hypnosis, from the conscious state to deep anesthesia (i.e., BSP).
Department of Anesthesiology, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
Bettina
B
Horn
Stefanie
S
Pilge
Eberhard F
EF
Kochs
Gudrun
G
Stockmanns
Andreas
A
Hock
Gerhard
G
Schneider
D000293:Adolescent; D000328:Adult; D000768:Anesthesia, General; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D003243:Consciousness / Q000187:drug effects*; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography; D005072:Evoked Potentials, Auditory / Q000187:drug effects*; D006801:Humans; D008297:Male; D008738:Methyl Ethers / Q000494:pharmacology; D016343:Monitoring, Intraoperative / Q000379:methods*; D011237:Predictive Value of Tests; D015742:Propofol / Q000494:pharmacology; D000077149:Sevoflurane; D055815:Young Adult
D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D008738:Methyl Ethers; D000077149:Sevoflurane; D015742:Propofol