2.2 | Data analysis
Statistical analysis was carried out using SAS version 9.4 software
(Cary, NC). Continuous variables were reported as medians and
interquartile ranges. Categorical variables were reported as frequencies
and percentages. For Table 1 and Table 2, Wilcoxon rank sum test was
used to test differences in distribution of continuous variables between
the two modes of ventilation. Chi-square test and Fisher’s exact test
were used for the comparison of proportions of categorical variables
between the two modes. P values of <0.05 were considered
statistically significant.
A multilevel linear mixed model was used to test for association between
gastric emptying rates and ventilation modes (MD-nCPAP, bCPAP)
accounting for emptying period (early, late) and gestational age (25+0
to 27+6 weeks, 28+0 to 34+6 weeks). All possible interactions, as well
as main effects, were included. Multivariable linear regression with
backward elimination was used to test for association between total
gastric emptying rates and ventilation mode accounting for GA. The
interaction between ventilation mode and GA group, as well as the main
effects were included in the model. Manual backward elimination was used
to identify main effects and interactions that were statistically
significant. In the case of a significant interaction term, post-hoc
paired comparisons were performed, and a Bonferroni adjustment was used
to account for multiple comparisons.