56 Chapter 3 from the data port or display of the ventilator under investigation. Secondary outcomes included: proportion of time in various degrees of hypoxaemia (SpO2 <80%, SpO2 80%-84%, SpO2 85-90%, SpO2 ≤90%) and hyperoxaemia (SpO2 >95%, SpO2 96%-98%, and SpO2 >98% while receiving supplemental oxygen); SpO2 and FiO2 coefficient of variation; frequency of 30 and 60 second episodes in hypoxaemia and hyperoxaemia; bradycardic episodes (heart rate <100 beats per minute for ≥10 consecutive seconds); frequency of FiO2 adjustments, both manual and automatic; and average oxygen exposure. Continuous data is represented as median (IQR) or mean ±SD as appropriate, with standard tests for normality. Time within particular SpO2 ranges was collated for each infant individually and expressed as proportion of usable recorded time. Differences in time in target range and other outcomes were assessed with the Wilcoxon matched-pairs test. The intention-to-treat principle was applied. Statistical analyses were performed by an analysist blinded to allocation using R 3.4.4 (R Core Team (2016). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL https://www.R-project.org/). Sample size calculation was based around data from previous studies of the two automated control algorithms. In a study using the CLiO2 in Leiden in preterm infants the proportion of time in the SpO2 TR was 60.4% (±15.6%). 24 In the first clinical study of the OxyGenie algorithm TR time was 78% (±15%). We considered a difference of 5% TR time a clinically relevant difference. For a two-sided paired statistical test, 44 infants would be needed assuming a standard deviation of 10% for a power of 90% and an alpha of 0.05. Because a non-parametric test would be used in the analysis we made a 15% addition to the sample size, as described by Lehmann,27 requiring a total of 50 participants. Early termination Just prior to study commencement, the SLE6000 ventilator was deployed as the standard device for neonatal respiratory support at LUMC. The AVEA ventilators were thereafter only used when an infant was included in the study. Based on historical data, we anticipated to complete recruitment in a year, which was also considered the maximum time competence of medical staff in working with both ventilators could be guaranteed. However, the recruitment rate was slower than expected and to ensure patient safety and an unbiased comparison of both oxygen control with the two ventilators the trial was terminated after a 12 month recruiting period.
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