title: High-frequency components of auditory evoked potentials are detected in responsive but not in unconscious patients.
abstract: BACKGROUND
  The dose-dependent suppression of midlatency auditory evoked potentials by general anesthetics has been proposed to measure depth of anesthesia. In this study, perioperatively recorded midlatency auditory evoked potentials were analyzed in a time-frequency space to identify significant changes induced by general anesthesia.
  
  
  METHODS
  Perioperatively recorded auditory evoked potentials of 19 patients, recorded at varying levels of anesthesia, were submitted to a multiscale analysis using the wavelet analysis. Energy contents of the signal were calculated in frequency bands 0-57.1 Hz, 57.1-114.3 Hz, 114.3-228.6 Hz, and 228.6-457.1 Hz. A Friedman test and a Dunn multiple comparisons test were performed to identify significant differences.
  
  
  RESULTS
  Statistical evaluation showed a highly significant decrease of the wavelet energies for the frequency bands 57.1-114.3 Hz (P < 0.0001), 114.3-228.6 Hz (P < 0.0001), and 228.6-457.1 Hz (P < 0.0001) for the measuring points representing deep general anesthesia. This decrease is accompanied by a decrease in the wavelet energy of the frequency band 0-57.1 Hz of no statistical significance (P = 0.021) (level of significance set to P = 0.01). The changes are most prominent in the poststimulus interval between 10 and 30 ms.
  
  
  CONCLUSIONS
  This study describes the presence of high-frequency components of the auditory evoked potential. The amount of these components is higher during responsiveness when compared to unconsciousness. Temporal localization of the high-frequency components within the auditory evoked potential shows that they represent a response to the auditory stimulus. Further studies are required to identify the source of these high-frequency components.
authors.affiliation: Department of Anesthesiology, Johann-Wolfgang-Goethe Universität Frankfurt, Frankfurt, Germany. scheller@em.uni-frankfurt.de
authors.forename: Bertram
authors.initials: B
authors.lastname: Scheller
authors.forename: Gerhard
authors.initials: G
authors.lastname: Schneider
authors.forename: Michael
authors.initials: M
authors.lastname: Daunderer
authors.forename: Eberhard F
authors.initials: EF
authors.lastname: Kochs
authors.forename: Bernhard
authors.initials: B
authors.lastname: Zwissler
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D000465:Algorithms; D000768:Anesthesia, General; D018686:Anesthetics, Intravenous / Q000008:administration & dosage; D003243:Consciousness / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects; D005072:Evoked Potentials, Auditory / Q000187:drug effects*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010880:Piperidines / Q000008:administration & dosage; D015742:Propofol / Q000008:administration & dosage; D000077208:Remifentanil
chemical_list: D018686:Anesthetics, Intravenous; D010880:Piperidines; D000077208:Remifentanil; D015742:Propofol