title: Analysis of the EEG bispectrum, auditory evoked potentials and the EEG power spectrum during repeated transitions from consciousness to unconsciousness.
abstract: We have compared the auditory evoked potential (AEP) index (a numerical index derived from the AEP), 95% spectral edge frequency (SEF), median frequency (MF) and the bispectral index (BIS) during alternating periods of consciousness and unconsciousness produced by target-controlled infusions of propofol. We studied 12 patients undergoing hip or knee replacement under spinal anaesthesia. During periods of consciousness and unconsciousness, respective mean values for the four measurements were: AEP index, 60.8 (SD 13.7) and 37.6 (6.5); BIS, 85.1 (8.2) and 66.8 (10.5); SEF, 24.2 (2.2) and 18.7 (2.1); and MF, 10.9 (3.3) and 8.8 (2.0). Threshold values with a specificity of 100% for a state of unconsciousness were: AEP index, 37 (sensitivity 52%); BIS, 55 (sensitivity 15%); and SEF, 16.0 (sensitivity 9%). There was no recorded value for MF that was 100% specific for unconsciousness. Of the four measurements, only AEP index demonstrated a significant difference (P < 0.05) between all mean values 1 min before recovery of consciousness and all mean values 1 min after recovery of consciousness. Our findings suggest that of the four electrophysiological variables, AEP index was best at distinguishing the transition from unconsciousness to consciousness.
authors.affiliation: University Department of Anaesthesia, HCI International Medical Centre, Clydebank, Scotland.
authors.forename: R J
authors.initials: RJ
authors.lastname: Gajraj
authors.forename: M
authors.initials: M
authors.lastname: Doi
authors.forename: H
authors.initials: H
authors.lastname: Mantzaridis
authors.forename: G N
authors.initials: GN
authors.lastname: Kenny
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000768:Anesthesia, General; D018686:Anesthetics, Intravenous; D019643:Arthroplasty, Replacement; D003243:Consciousness / Q000502:physiology*; D004569:Electroencephalography; D005072:Evoked Potentials, Auditory; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D015742:Propofol; D012680:Sensitivity and Specificity; D014474:Unconsciousness / Q000503:physiopathology*
chemical_list: D018686:Anesthetics, Intravenous; D015742:Propofol