Statistical analysis

The data were compiled using a standard spreadsheet application (Excel, Microsoft, Redmond, WA, USA) and were analyzed using the IBM SPSS Statistics ver. 22 (IBM Corp., Armonk, NY, USA). We generated descriptive statistics and presented them as frequencies and percentages for the categorical data and median with interquartile range for the continuous data. In comparison of the intubation time among the 4 devices, the Friedman test was used for continuous variables. A post-hoc analysis was conducted with the Wilcoxon rank-sum test using the Bonferroni correction. The Kaplan-Meier analysis was performed to analyze the cumulative success rate regarding intubation time. A post-hoc analysis was also performed using the log-rank test with the Bonferroni correction. For all analyzed data, P-value was calculated by two-sided tests and P<0.05 was considered statistically significant. In contrast, in post-hoc analysis, P<0.0083 was considered significant.