Statistical analysis
postoperative atelectasis
POSTOPERATIVE ATELECTASIS

According to the distribution of the data evaluated using the Kolmogorov-Smirnov test, continuous variables were analyzed using the two-sample t-test or Mann-Whitney U test and presented as mean ± standard deviation (SD) or median [interquartile range (IQR)]. Categorical variables were analyzed using the Chi-square test or Fisher’s exact test and reported as numbers and percentages. The primary outcome (the percentage of postoperative atelectasis volume) was normalized using the square root transformation and then analyzed using the two-sample t-test. Moreover, the Mann-Whitney U test was performed to assess the differences in the unnormalized primary outcome data between the two groups. The differences in the oxygenation index at the end of surgery between the two groups were compared, with the oxygenation index before anesthesia as a covariate. A two-sided 
We handled missing normalized primary outcome data using multiple imputation by chained equations (MICE), and the iterations were set to 5 [