Pre-oxygenation in the obese patient: effects of position on tolerance to apnoea

Br J Anaesth. 2005 Nov;95(5):706-9. doi: 10.1093/bja/aei231. Epub 2005 Sep 2.


Background: In obese patients, reduced functional residual capacity exacerbated by supine position might decrease the effectiveness of pre-oxygenation and the tolerance to apnoea. The aim of this study was to compare the effect of body posture during pre-oxygenation, sitting or supine, on its effectiveness in obese patients.

Methods: Forty obese patients (BMI > or =35 kg m(-2)) undergoing surgery with general anaesthesia were randomly assigned to one of two groups: Group 1 (sitting, n=20) or Group 2 (supine, n=20). In the predetermined body position, pre-oxygenation was achieved with eight deep breaths within 60 s and an oxygen flow of 10 litre min(-1). After rapid sequence induction of anaesthesia in decubitus position, the trachea was intubated and the patient was left apneic and disconnected from the anaesthesia circuit until Sp(o2) decreased to 90%. The time taken for desaturation to 90% from the end of induction of anaesthesia was recorded. Arterial blood oxygen tension was measured before (baseline) and after pre-oxygenation. Values were compared with two-way anova and unpaired Student's t-test.

Results: Oxygen and carbon dioxide tensions were similar between groups, both at baseline and after pre-oxygenation. However, the mean time to desaturation to 90% was significantly longer in the sitting group compared with the supine group [mean (SD): 214 (28) vs 162 (38) s, P<0.05].

Conclusions: Pre-oxygenation in sitting position significantly extends the tolerance to apnoea in obese patients when compared with the supine position.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Anesthesia, General
  • Anthropometry
  • Apnea / prevention & control*
  • Carbon Dioxide / blood
  • Female
  • Humans
  • Intraoperative Complications / prevention & control*
  • Male
  • Middle Aged
  • Obesity / complications*
  • Oxygen / blood
  • Oxygen Inhalation Therapy / methods*
  • Partial Pressure
  • Posture
  • Preoperative Care / methods*
  • Supine Position


  • Carbon Dioxide
  • Oxygen