Optimal oxygen concentration during induction of general anesthesia

Background: The use of 100% oxygen during induction of anesthesia may produce atelectasis. The authors investigated how different oxygen concentrations affect the formation of atelectasis and the fall in arterial oxygen saturation during apnea. Methods: Thirty-six healthy, nonsmoking women were randomized to breathe 100, 80, or 60% oxygen for 5 min during the induction of general anesthesia. Ventilation was then withheld until the oxygen saturation, assessed by pulse oximetry, decreased to 90%. Atelectasis formation was studied with computed tomography. Results: Atelectasis in a transverse scan near the diaphragm after induction of anesthesia and apnea was 9.8 +/- 5.2 cm(2) (5.6 +/- 3.4% of the total lung area; mean +/- SD), 1.3 +/- 1.2 cm(2) (0.6 +/- 0.7%), and 0.3 +/- 0.3 cm(2) (0.2 +/- 0.2%) in the groups breathing 100, 80, and 60% oxygen, respectively (P < 0.01). The corresponding times to reach 90% oxygen saturation were 411 84, 303 +/- 59, and 213 +/- 69 s, respectively (P < 0.01). Conclusion: During routine induction of general anesthesia, 80% oxygen for oxygenation caused minimal atelectasis, but the time margin before unacceptable desaturation occurred was significantly shortened compared with 100% oxygen.