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 cm2 (5.6 +/- 3.4% of the total lung area; mean +/- SD), 1.3 +/- 1.2 cm2 (0.6 +/- 0.7%), and 0.3 +/- 0.3 cm2 (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).


CONCLUSIONS
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.
Edmark
Lennart
L
Department of Anesthesiology and Intensive Care, Central Hospital, Västerås, and Research Associate, Department of Medical Sciences, Clinical Physiology, University Hospital, Uppsala, Sweden. lennart.edmark@ltvastmanland.se
Kostova-Aherdan
Kamelia
K
Enlund
Mats
M
Hedenstierna
Göran
G
D000328:Adult; D000368:Aged; D000399:Air Pressure; D000768:Anesthesia, General; D001049:Apnea / Q000209:etiology; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000209:etiology; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D010100:Oxygen / Q000008:administration & dosage* / Q000009:adverse effects / Q000097:blood; D011175:Positive-Pressure Respiration; D001261:Pulmonary Atelectasis / Q000209:etiology; D012121:Respiration, Artificial; D014057:Tomography, X-Ray Computed
D010100:Oxygen