• Tatsuya Yoshimura, Kenichi Ueda, Akihito Kakinuma, Jun Sawai, and Yoshinori Nakata.
• From the *Department of Anesthesiology, Teikyo University Hospital, Tokyo, Japan; †Department of Anesthesia, The University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, Iowa; and ‡Graduate School of Public Health, Teikyo University, Tokyo, Japan.
• Anesth. Analg.. 2014 Mar 1;118(3):666-70.

BackgroundEffective lung collapse of the nonventilated lung can facilitate thoracic surgery. Previous studies showed that using a bronchial blocker could delay the time of lung collapse compared with using a double-lumen endotracheal tube. We hypothesized that the use of nitrous oxide (N2O) in the inspired gas mixture during 2-lung ventilation would lead to clinically relevant improvement of lung collapse during subsequent 1-lung ventilation with a bronchial blocker.MethodsFifty patients were randomized into 2 groups: N2O (n =26) or O2 (n = 24). The N2O group received a gas mixture of oxygen and N2O (FIO2 = 0.5), and the O2 group received 100% oxygen until the start of 1-lung ventilation. Lung isolation was achieved with an Arndt® wire-guided bronchial blocker (Cook® Critical Care, Bloomington, IN. After turning patients to the lateral decubitus position, the cuff of the bronchial blocker was inflated under fiberoptic bronchoscopy surveillance, and thereafter, the dependent lung was ventilated with 100% oxygen during 1-lung ventilation in both groups. Surgeons blinded to the randomization evaluated the degree of lung collapse by using a verbal rating scale (lung collapse scale, 0 = no collapse to 10 = complete collapse) at 5 minutes after opening the pleura. Also, as secondary outcomes, lung collapse at 1 and 10 minutes were evaluated.ResultsThe score on the lung collapse scale in the N2O group was significantly higher compared with the O2 group at 5 minutes after opening the pleura (7 vs 5, P < 0.001, WMWodds = 7.3, 95% confidence interval (CI), 6.0 to 9.0). It was also higher in the N2O group at 10 minutes (10 vs 7, P < 0.001, WMWodds = 10.1, 95% CI, 1.9-13.3). The lung collapse scale between groups was not significant at 1 minute after opening the pleura (2 vs 2, P = 0.76, WMWodds = 1.1, 95% CI, 0.96-1.2). None of the patients developed hypoxia (SpO2 <92%) during 1-lung ventilation.ConclusionsFilling the lung with 50% N2O before 1-lung ventilation facilitated lung collapse 5 minutes after opening the chest compared with 100% oxygen when a bronchial blocker was used. The N2O/O2 mixture (FIO2 = 0.5) did not have a harmful effect on subsequent arterial oxygenation during 1-lung ventilation.

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