title: [The correlation of middle ear pressure variations with mastoid pneumatization during nitrous oxide administration].
abstract: BACKGROUND
  The present study evaluated the relationship between the middle ear (ME) pressure increase rate (PIR) and the mastoid size as well as the effect of mastoid size on the incidence of nausea and vomiting during nitrous oxide (N2O) anesthesia.
  
  
  METHODS
  Twelve healthy male volunteers were recruited. The extent of mastoid pneumatization was measured planimetrically using a mastoid X-ray (Schuller's view). The ears were then divided into a small or large mastoid group according to the median value. The ME pressure was compared just before each increase to 33%, 50%, and 67% N2O. Using the ME pressure curve, the PIR for the first peak of the curve steepness was calculated.
  
  
  RESULTS
  Increasing the end-tidal N2O concentration to 50% and 67% in the large mastoid group and to 33%, 50%, and 67% in the small mastoid group significantly increased the ME pressure. The PIR in the ears in the large mastoid group was significantly lower and the incidence of nausea was 33% in the small mastoid group during 33% N2O anesthesia.
  
  
  CONCLUSIONS
  A higher PIR in the ears and a higher incidence of nausea were observed in the small mastoid group, compared with the large mastoid group.
authors.affiliation: Department of Anesthesiology, Tokyo Women's Medical University Medical Center East, Tokyo 166-8567.
authors.forename: Junko
authors.initials: J
authors.lastname: Ichikawa
authors.forename: Kumiko
authors.initials: K
authors.lastname: Taira
authors.forename: Keiko
authors.initials: K
authors.lastname: Nishiyama
authors.forename: Mitsuharu
authors.initials: M
authors.lastname: Kodaka
authors.forename: Makiko
authors.initials: M
authors.lastname: Komori
authors.forename: Makoto
authors.initials: M
authors.lastname: Ozaki
mesh_terms: D000328:Adult; D000769:Anesthesia, Inhalation; D004432:Ear, Middle / Q000502:physiology*; D006801:Humans; D008297:Male; D008416:Mastoid / Q000033:anatomy & histology / Q000502:physiology*; D009609:Nitrous Oxide / Q000494:pharmacology*; D011312:Pressure
chemical_list: D009609:Nitrous Oxide