title: Preoxygenation is more effective in the 25 degrees head-up position than in the supine position in severely obese patients: a randomized controlled study.
abstract: BACKGROUND
  Class III obese patients have altered respiratory mechanics, which are further impaired in the supine position. The authors explored the hypothesis that preoxygenation in the 25 degrees head-up position allows a greater safety margin for induction of anesthesia than the supine position.
  
  
  METHODS
  A randomized controlled trial measured oxygen saturation and the desaturation safety period after 3 min of preoxygenation in 42 consecutive (male:female 13:29) severely obese (body mass index > 40 kg/m) patients who were undergoing laparoscopic adjustable gastric band surgery and were randomly assigned to the supine position or the 25 degrees head-up position. Serial arterial blood gases were taken before and after preoxygenation and 90 s after induction. After induction, ventilation was delayed until blood oxygen saturation reached 92%, and this desaturation safety period was recorded.
  
  
  RESULTS
  The mean body mass indexes for the supine and 25 degrees head-up groups were 47.3 and 44.9 kg/m, respectively (P = 0.18). The group randomly assigned to the 25 degrees head-up position achieved higher preinduction oxygen tensions (442 +/- 104 vs. 360 +/- 99 mmHg; P = 0.012) and took longer to reach an oxygen saturation of 92% (201 +/- 55 vs. 155 +/- 69 s; P = 0.023). There was a strong positive correlation between the induction oxygen tension achieved and the time to reach an oxygen saturation of 92% (r = 0.51, P = 0.001). There were no adverse events associated with the study.
  
  
  CONCLUSIONS
  Preoxygenation in the 25 degrees head-up position achieves 23% higher oxygen tensions, allowing a clinically significant increase in the desaturation safety period--greater time for intubation and airway control. Induction in the 25 degrees head-up position may provide a greater safety margin for airway control.
authors.affiliation: Australian Center for Obesity Research and Education, Monash University, Alfred Hospital, Melbourne 3181, Victoria, Australia. john.dixon@med.monash.edu.au
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Dixon
authors.forename: John B
authors.initials: JB
authors.lastname: Dixon
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Carden
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Burn
authors.forename: Linda M
authors.initials: LM
authors.lastname: Schachter
authors.forename: Julie M
authors.initials: JM
authors.lastname: Playfair
authors.forename: Cheryl P
authors.initials: CP
authors.lastname: Laurie
authors.forename: Paul E
authors.initials: PE
authors.lastname: O'Brien
mesh_terms: D000328:Adult; D000768:Anesthesia, General / Q000379:methods*; D001784:Blood Gas Analysis; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000097:blood* / Q000601:surgery / Q000628:therapy; D010101:Oxygen Consumption / Q000502:physiology; D010102:Oxygen Inhalation Therapy / Q000379:methods*; D016683:Supine Position / Q000502:physiology*