Time-frequency balanced spectral entropy as a measure of anesthetic drug effect in central nervous system during sevoflurane, propofol, and thiopental anesthesia.
BACKGROUND
Time-frequency balanced spectral entropy of electroencephalogram (EEG) and frontal electromyogram (FEMG) is a novel measure of hypnosis during anesthesia. Two Entropy parameters are described: Response entropy (RE) is calculated from EEG and FEMG; and State Entropy (SE) is calculated mainly from EEG. This study was performed to validate their performance during transition from consciousness to unconsciousness under different anesthetic agents.


METHODS
Response entropy, SE [S/5 Entropy Module, M-ENTROPY (later in text: Entropy), Datex-Ohmeda Division, Instrumentarium Corp., Helsinki, Finland] and BIS (BIS XP, A-2000, Aspect Medical Systems, Newton, MA) data were collected from 70 patients; 30 anesthetized with propofol 2 mg kg-1, 20 with sevoflurane inhalation, and 20 with thiopental 5 mg kg-1. Loss and regaining of consciousness (LOC, ROC) was tested every 10 s, and sensitivity, specificity, and prediction probability (Pk) were calculated. Behavior of the indices was studied.


RESULTS
Sensitivity, specificity, and Pk values for consciousness were high and similar for all indices. During regaining of consciousness after propofol bolus, RE, SE, and BIS values recovered by 81 +/- 22%, 75 +/- 26%, and 59 +/- 18% (mean +/- SD), respectively, from the minimum relative to their baseline. After thiopental bolus, RE, SE, and BIS values recovered by 86+/-21%, 88 +/- 13%, and 63 +/- 14%, respectively. The relative rise was higher in RE and SE compared with BIS (P < 0.01). During deep levels of hypnosis, RE and SE decreased monotonously as a function of burst suppression ratio, while BIS showed biphasic behavior. On average, RE indicated emergence from anesthesia 11 s earlier than SE, and 12.4 s earlier than BIS.


CONCLUSIONS
All indices, RE, SE, and BIS, distinguished excellently between conscious and unconscious states during propofol, sevoflurane, and thiopental anesthesia. During burst suppression, Entropy parameters RE and SE, but not BIS, behave monotonously. During regaining of consciousness after a thiopental or propofol bolus, RE and SE values recovered significantly closer to their baseline values than did BIS. Response entropy indicates emergence from anesthesia earlier than SE or BIS.
Vakkuri
A
A
Department of Anesthesia, Surgical Hospital, Helsinki University Hospital, Kasarmikatu 11-13, PO Box 263, 00029 HUS, Helsinki, Finland. anne.vakkuri@hus.fi
Yli-Hankala
A
A
Talja
P
P
Mustola
S
S
Tolvanen-Laakso
H
H
Sampson
T
T
Viertiö-Oja
H
H
D000293:Adolescent; D000328:Adult; D000368:Aged; D000777:Anesthetics / Q000494:pharmacology*; D004569:Electroencephalography / Q000187:drug effects*; D004576:Electromyography / Q000187:drug effects; D019277:Entropy; D006801:Humans; D008738:Methyl Ethers / Q000494:pharmacology*; D008875:Middle Aged; D015742:Propofol / Q000494:pharmacology*; D012680:Sensitivity and Specificity; D000077149:Sevoflurane; D013874:Thiopental / Q000494:pharmacology*; D013997:Time Factors
D000777:Anesthetics; D008738:Methyl Ethers; D000077149:Sevoflurane; D013874:Thiopental; D015742:Propofol