Page 54 - Physiological based CPAP for preterm infants at birth Tessa Martherus
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Chapter 2
Ethics
The local institutional Research Ethics Committee of the LUMC and the University Hospital of Cologne and the LUMC approved the study protocol and issued a statement of no objection for performing this research.
Sample Size Calculation
Sample size was calculated based on the oxygen saturation of an independent sample. In the clinical trial of Dekker et al. (32) infants below 28 weeks of gestation received 5-8 cmH2O of CPAP according to the LUMC local protocol. The mean ± SD oxygen saturation in the first 7 min after birth was 68 ± 13%. To detect an absolute increase of 10% in SpO2 when using higher pressure levels, using a power of 80% and α=0.05, 54 infants (28 in each group) where calculated to be required. Infants included in the clinical trial (32), thus included in the sample size calculation, were excluded in this study.
Statistical Analyses
Data were analyzed using IBM SPSS Statistics version 23.0 (IBM Software, Chicago, Illinois, USA, 2016). Categorical data were analyzed using Related-Samples McNemar tests and are presented as n (%). Numerical data were assessed for normality by visual inspection of histograms. The data were analyzed by the Related-Samples Wilcoxon Signed Rank test and presented as median (IQR).
Physiological parameters were compared between groups over time using a linear mixed-effect regression model, accounting for the relation between multiple measurements of the same infant with a heterogeneous first-order autoregressive covariance structure on the residuals. Group, time and group∗time interaction were included as fixed factors in the model. The model corrected for Apgar score ‘1 minute after birth. As all infants born at the University Hospital of Cologne were born by cesarean section, we were unable to correct for mode of delivery. Therefore, a sensitivity analysis was also performed including infants born by cesarean section only. The SpO2 and FiO2 variables were transformed using logit transformations: Ln(X/(1-X)) for SpO2 and Ln(79/100∗(X−0.21)/(1-79/100∗(X−0.21))) for FiO2, to ensure that the estimated values of both parameters remained between 0-100% and 21-100%, respectively, in the statistical model. Raw data is presented as median (IQR). P-values <0.05 were considered statistically significant and reported p-values are two sided.
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