A randomised trial comparing 80% and 100% inspired oxygen concentrations for time to adequate preoxygenation using end-tidal oxygen concentration targets.

BACKGROUND AND AIMS: Preoxygenation with 100% oxygen is associated with absorption atelectasis. This study compared 80% and 100% fractional inspired oxygen concentration (FiO2) for the time to achieve adequate preoxygenation, defined by end-tidal oxygen (EtO2). Secondary outcomes included the incidence of postoperative atelectasis, proportion of patients requiring more than 3 minutes for preoxygenation, haemodynamic changes, and desaturation. METHODS: Two-hundred patients for general anaesthesia were randomly divided into either Group I or Group S, the intervention and the standard practice groups, and were preoxygenated with 80% and 100% FiO2, respectively. The time taken to reach an EtO2 of 10% below the administered FiO2 was considered the time to adequate preoxygenation. A lung ultrasonography was performed at baseline and again immediately after extubation. Independent t-test or Mann-Whitney U test and the Chi-square test were used for continuous and nominal categorical data, respectively. Non-inferiority was concluded if the lower bound of the confidence interval remained above the predefined non-inferiority margin of -15 seconds. RESULTS: The median preoxygenation time was comparable between groups: 95 s [interquartile range (IQR) 70-133] and 99.5 s (IQR 80.3-140) in Group I and S, respectively (P = 0.484; 95% confidence interval -21 to 11). Non-inferiority was not demonstrated. The effect size was small (r = -0.096), indicating minimal clinical difference. However, atelectasis was significantly higher in Group S (31.9%) compared to Group I (8.6%) (P = 0.002). CONCLUSION: Non-inferiority of FiO2 80% with 100% could not be established within the prespecified margin, though the median time to achieve adequate preoxygenation was comparable.