title: Effect of head elevation on passive upper airway collapsibility in normal subjects during propofol anesthesia.
abstract: BACKGROUND
  Head elevation can restore airway patency during anesthesia, although its effect may be offset by concomitant bite opening or accidental neck flexion. The aim of this study is to examine the effect of head elevation on the passive upper airway collapsibility during propofol anesthesia.
  
  
  METHODS
  Twenty male subjects were studied, randomized to one of two experimental groups: fixed-jaw or free-jaw. Propofol infusion was used for induction and to maintain blood at a constant target concentration between 1.5 and 2.0 μg/ml. Nasal mask pressure (PN) was intermittently reduced to evaluate the upper airway collapsibility (passive PCRIT) and upstream resistance (RUS) at each level of head elevation (0, 3, 6, and 9 cm). The authors measured the Frankfort plane (head flexion) and the mandible plane (jaw opening) angles at each level of head elevation. Analysis of variance was used to determine the effect of head elevation on PCRIT, head flexion, and jaw opening within each group.
  
  
  RESULTS
  In both groups the Frankfort plane and mandible plane angles increased with head elevation (P < 0.05), although the mandible plane angle was smaller in the free-jaw group (i.e., increased jaw opening). In the fixed-jaw group, head elevation decreased upper airway collapsibility (PCRIT ~ -7 cm H₂O at greater than 6 cm elevation) compared with the baseline position (PCRIT ~ -3 cm H₂O at 0 cm elevation; P < 0.05).
  
  
  CONCLUSIONS
  : Elevating the head position by 6 cm while ensuring mouth closure (centric occlusion) produces substantial decreases in upper airway collapsibility and maintains upper airway patency during anesthesia.
authors.affiliation: Department of Clinical Physiology, Nagasaki University Graduate School of Biomedical Science, Nagasaki, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Takao
authors.initials: T
authors.lastname: Ayuse
authors.forename: Yuko
authors.initials: Y
authors.lastname: Hoshino
authors.forename: Shinji
authors.initials: S
authors.lastname: Kurata
authors.forename: Shunji
authors.initials: S
authors.lastname: Moromugi
authors.forename: Hartmut
authors.initials: H
authors.lastname: Schneider
authors.forename: Jason P
authors.initials: JP
authors.lastname: Kirkness
authors.forename: Alan R
authors.initials: AR
authors.lastname: Schwartz
authors.forename: Kumiko
authors.initials: K
authors.lastname: Oi
mesh_terms: D000328:Adult; D000402:Airway Obstruction / Q000517:prevention & control*; D000771:Anesthesia, Intravenous; D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006257:Head; D006801:Humans; D007568:Jaw / Q000502:physiology; D008297:Male; D009333:Neck; D015742:Propofol / Q000494:pharmacology*; D020181:Sleep Apnea, Obstructive / Q000628:therapy
chemical_list: D018686:Anesthetics, Intravenous; D015742:Propofol