Anesthesiology, V 120 • No 4 1050 April 2014 We read not only with interest but also with some surprise the review on high intraoperative oxygen concentration by Hovaguimian et al. 1 that appeared recently in ANESTHE- SIOLOGY. he authors selected 9 to 11 of 21 studies and by a meta-analysis they concluded that “Intraoperative high inspired oxygen fraction decreases the risk of surgical-site infection in surgical patients receiving prophylactic antibi- otics, has a weak beneicial efect on nausea, and does not increase the risk of postoperative atelectasis.” We notice that two of the four largest studies that were included in the meta- analysis (434 and 1,386 patients) showed no better result with high oxygen 2,3 and that the largest study (2,012 patients) 4 was designed to evaluate efects of nitrous oxide (0 or 70%) rather than oxygen. In another three studies, the nitrous oxide con- centration was also varied. his must be considered a con- founding factor when aiming at an analysis of oxygen efects. Among the remaining studies, one was discontinued because of more adverse efects by the high oxygen concentration. 5 In a study by Meyhof et al., 6 high oxygen concentrations increased mortality in patients undergoing cancer surgery. Whether high oxygen concentrations are good or harmful in a surgical wound can thus still be discussed and is indeed a hot issue in redox signaling and tissue repair. 7 he other result that surprises us is the conclusion that high oxygen concentration (80 vs. 30%) does not increase the risk of postoperative atelectasis. he anesthesia was pre- sumably induced by preoxygenation with 100% oxygen in both groups and this causes atelectasis within a few min- utes of anesthesia. 8 he atelectasis remains during the whole anesthetic period and the switch to either 30 or 80% oxy- gen does not add much to the initial atelectasis. 9 Moreover, the atelectasis remains for some time postoperatively. One may rather conclude that with present standard routines for anesthesia and ventilation atelectasis will develop in the vast majority of patients (90% or more) with no additional efect by the intraoperative oxygen concentration. If the intention is to avoid atelectasis, the lung has to be recruited after induction of anesthesia. Continuation with 30 or 80% oxygen will then show a clear diference between the groups with more atelectasis in the high oxygen group. 9 A rationale to avoid atelectasis, besides its impairment of oxygenation, may be that proliferation and translocation of bacteria to promote pneumonia have been shown in the atelectatic lung in anesthetized, mechanically ventilated animals. 10 All taken together, whether high or low oxygen concentration is to be used, atelectasis can and should be avoided. Acknowledgments Supported by grants from the Swedish Research Council, No. 5315, Stockholm, Sweden, and the Swedish Heart-Lung Fund, Stockholm, Sweden. Competing Interests The authors declare no competing interests. Goran Hedenstierna, M.D., Ph.D., Lennart Edmark, M.D., Ph.D. University Hospital, Hedenstierna Laboratory, Uppsala, Sweden (G.H.). goran.hedenstierna@medsci.uu.se References 1. Hovaguimian F, Lysakowski C, Elia N, Tramèr MR: Effect of intraoperative high inspired oxygen fraction on surgical site infection, postoperative nausea and vomiting, and pulmo- nary function: Systematic review and meta-analysis of ran- domized controlled trials. ANESTHESioLogy 2013; 119:303–16 2. Meyhoff CS, Wetterslev J, Jorgensen LN, Henneberg SW, Høgdall C, Lundvall L, Svendsen PE, Mollerup H, Lunn TH, Simonsen i, Martinsen KR, Pulawska T, Bundgaard L, Bugge L, Hansen Eg, Riber C, gocht-Jensen P, Walker LR, Bendtsen A, Johansson g, Skovgaard N, Heltø K, Poukinski A, Korshin A, Walli A, Bulut M, Carlsson PS, Rodt SA, Lundbech LB, Rask H, Buch N, Perdawid SK, Reza J, Jensen KV, Carlsen Cg, Jensen FS, Rasmussen LS; PRoXi Trial group: Effect of high perioperative oxygen fraction on surgical site infection and pulmonary complications after abdominal surgery: The PRoXi randomized clinical trial. JAMA 2009; 302:1543–50 3. Thibon P, Borgey F, Boutreux S, Hanouz JL, Le Coutour X, Parienti JJ: Effect of perioperative oxygen supplementation on 30-day surgical site infection rate in abdominal, gyneco- logic, and breast surgery: The iSo2 randomized controlled trial. ANESTHESioLogy 2012; 117:504–11 4. Myles PS, Leslie K, Chan MT, Forbes A, Paech MJ, Peyton P, Silbert BS, Pascoe E; ENigMA Trial group: Avoidance of nitrous oxide for patients undergoing major surgery: A ran- domized controlled trial. ANESTHESioLogy 2007; 107:221–31 5. Pryor Ko, Fahey TJ iii, Lien CA, goldstein PA: Surgical site infection and the routine use of perioperative hyperoxia in a general surgical population: A randomized controlled trial. JAMA 2004; 291:79–87 6. Meyhoff CS, Jorgensen LN, Wetterslev J, Christensen KB, Rasmussen LS; PRoXi Trial group: increased long-term mor- tality after a high perioperative inspiratory oxygen fraction during abdominal surgery: Follow-up of a randomized clini- cal trial. Anesth Analg 2012; 115:849–54 7. Jiang F, Zhang y, Dusting gJ: NADPH oxidase-mediated redox signaling: Roles in cellular stress response, stress tol- erance, and tissue repair. Pharmacol Rev 2011; 63:218–42 8. Rothen HU, Sporre B, Engberg g, Wegenius g, Reber A, Hedenstierna g: Prevention of atelectasis during general anaesthesia. Lancet 1995; 345:1387–91 9. Hedenstierna g, Edmark L: Mechanisms of atelectasis in the perioperative period. Best Pract Res Clin Anaesthesiol 2010; 24:157–69 10. van Kaam AH, Lachmann RA, Herting E, De Jaegere A, van iwaarden F, Noorduyn LA, Kok JH, Haitsma JJ, Lachmann B: Reducing atelectasis attenuates bacterial growth and trans- location in experimental pneumonia. Am J Respir Crit Care Med 2004; 169:1046–53 (Accepted for publication November 19, 2013.) Does High Oxygen Concentration Reduce Postoperative Infection? To the Editor: Copyright © 2014, the American Society of Anesthesiologists, Inc. Lippincott Williams & Wilkins. Anesthesiology 2014; 120:1050-9 CORRESPONDENCE