title: Influence of hypobaric hypoxia on bispectral index and spectral entropy in volunteers.
abstract: BACKGROUND
  Hypoxia has been shown to change electroencephalogram parameters including frequency and amplitude, and may thus change bispectral index (BIS) and spectral entropy values. If hypoxia per se changes BIS and spectral entropy values, BIS and spectral entropy values may not correctly reflect the depth of anaesthesia during hypoxia. The aim of this study was to examine the changes in BIS and spectral entropy values during hypobaric hypoxia in volunteers.
  
  
  METHODS
  The study was conducted in a high-altitude chamber with 11 volunteers. After the subjects breathed 100% oxygen for 15 min at the ground level, the simulated altitude increased gradually to the 7620 m (25,000 ft) level while the subjects continued to breathe oxygen. Then, the subjects discontinued to breath oxygen and breathed room air at the 7620 m level for up to 5 min until they requested to stop hypoxic exposure. Oxygen saturation (SpO2), heart rate, 95% spectral edge frequency (SEF), BIS, response entropy (RE), and state entropy (SE) of spectral entropy were recorded throughout the study period.
  
  
  RESULTS
  Of the 11 subjects, seven subjects who underwent hypoxic exposure for 4 min were analysed. SpO2 decreased to 69% at the 7620 m level without oxygen. However, SEF, BIS, RE, and SE before and during hypoxic exposure were almost identical.
  
  
  CONCLUSIONS
  These data suggest that hypoxia of oxygen saturation around 70% does not have a strong effect on BIS and spectral entropy.
authors.affiliation: Department of Anesthesiology, National Defense Medical College, Tokorozawa, Japan. tikeda@nyc.odn.ne.jp
authors.forename: T
authors.initials: T
authors.lastname: Ikeda
authors.forename: S
authors.initials: S
authors.lastname: Yamada
authors.forename: T
authors.initials: T
authors.lastname: Imada
authors.forename: H
authors.initials: H
authors.lastname: Matsuda
authors.forename: T
authors.initials: T
authors.lastname: Kazama
mesh_terms: D000328:Adult; D000399:Air Pressure; D000531:Altitude; D001273:Atmosphere Exposure Chambers; D004569:Electroencephalography; D019277:Entropy; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D015656:Respiratory Mechanics / Q000502:physiology; D055815:Young Adult
chemical_list: D010100:Oxygen