• MiHye Park, Kangha Jung, Woo Seog Sim, Duk Kyung Kim, In Sun Chung, Ji Won Choi, Eun Jee Lee, Nam Young Lee, and Jie Ae Kim.
• Department of Anesthesiology and Pain Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine in Seoul, South Korea.
• J Clin Anesth. 2021 Sep 1; 72: 110285.

Study ObjectiveWe evaluated the feasibility of use and effects on postoperative atelectasis and complications of lower inspired oxygen fraction (FIO2) compared to conventional oxygen therapy.DesignSingle center, randomized clinical trial.SettingUniversity hospital, operating room and postoperative recovery area.PatientsOne hundred ninety patients aged ≥50 with an American Society of Anesthesiologists physical status of I-III who underwent abdominal surgery with general anesthesia.InterventionsParticipants were randomly assigned to either the low FIO2 group (intraoperative: FIO2 0.35, during induction and recovery: FIO2 0.7) or the conventional FIO2 group (intraoperative: FIO2 0.6, during induction and recovery: FIO2 1.0).MeasurementsThe primary outcome was postoperative atelectasis measured with lung ultrasonography at postoperative 30 min in the post-anesthesia care unit (consolidation score: each region 0-3, 12 region, total score range of 0 to 36, a lower score indicating better aeration).Main ResultsSeven patients in the low FIO2 group were omitted from the study due to changing FIO2 during intervention (7/95 (8.4%) vs. 2/95 (2.1%), p = 0.088; low FIO2 group vs. conventional FIO2 group). Overall, atelectasis was detected in 29.7% (51/172) of patients 30 min after surgery by lung ultrasound and 40.1% (69/172) of patients after 2 days after surgery by chest X-ray. The scores of lung ultrasonography and the incidence of significant atelectasis (consolidation score ≥ 2 at any region) were lower in the low FIO2 group than in the conventional FIO2 group (median [IQR]: 3 [1,6] vs. 7 [3,9], p < 0.001 and 17/85 (20%) vs. 34/87 (39%), RR: 0.512 [95% CI: 0.311-0.843], p = 0.006, respectively). The incidence of surgical site infection and length of hospitalization were not significantly different between the two groups.ConclusionsBased on our findings, decreased inspired oxygen fraction during anesthesia and recovery did not cause hypoxic events, but instead reduced immediate postoperative atelectasis. The use of intraoperative conventional higher inspired oxygen did not afford any clinical advantages for postoperative recovery in abdominal surgery.Copyright © 2021 Elsevier Inc. All rights reserved.

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