All analyses were conducted on an intention-to-treat basis. Values are reported as mean and standard deviation. Continuous variables were compared with the use of the unpaired t-test or the Wilcoxon rank-sum test, depending on their distributional characteristics. Categorical variables were compared with the use of Fisher's exact test or the chi-square test, when appropriate. The Kaplan-Meier curve for intubation rate was plotted and was compared by the log-rank and Wilcoxon tests. All reported P values are two-sided.