Determination of sample size
Using G-power (version3.1.9.2) software to calculate the sample size, the main research index of this study was the difference in pulse oxygen saturation of children after extubation. According to the results of the previous pre-test (a total of 90 children were included, among which the mean pulse oxygen saturation after extubation with the supine position was 95.7%, the mean pulse oxygen saturation with the head-high 15°in lateral position was 96.2%, and the mean pulse oxygen saturation with the head-high 15°in lateral position was 96.3%), the setting = 0.05, power = 0.95, 122 children were included in each group. Considering that the dropout rate was 0.2, according to the formula dropout rate = number of dropouts / total sample size, a total of 153 children should be included in each group.