Statistical analysis
All quantitative variables are summarized as mean and standard
deviation (SD), and the qualitative variables are summarized as
frequency and percentage. The results are reported separately for
each of the two groups (NIV use and no NIV use). The statistical
analysis was conducted by parametric or non-parametric test,
according to the distribution of variables as assessed by the
Shapiro-Wilk test. Student’s t-test for unpaired data was used to
compare the quantitative variables between the two groups (NIV
use and no NIV use), while the chi-squared test was used for
qualitative variables. The unadjusted odds ratio (OR) for NIV use
vs. no NIV use and its associated 95% confidence interval (95%
CI) were calculated for each variable by a logistic regression
analysis. One-way ANOVA for repeated measures was used with
the clinical parameters, ABG results and lactate values to evaluate
the effects of NIV use over 24 h. Contrast analysis, a priori
specified, was used for comparisons versus previous time points.