Hylke Salverda

108 Chapter 6 Materials and methods Study design A retrospective observational study was performed in the NICU of the Leiden University Medical Center (LUMC). This is a tertiary-level perinatal centre with an average of 100 intensive care admissions per year of infants born before 30 weeks of gestation. The ethical board of the LUMC provided a statement of no objection for obtaining and publishing the anonymised data. Infants born from 24+0 until 29+6 weeks of gestation and admitted to the NICU between May 1st 2012 and December 31st 2018 were included in the study. Infants were excluded from the analysis if admitted >24 hours after birth, had major congenital abnormalities, or required no invasive or non-invasive respiratory support during their admission. The pre-implementation cohort consisted of infants admitted between May 1st 2012 and June 17th 2015 who received manual FiO 2 titration from bedside staff according to local guidelines. The post-implementation cohort was composed of infants admitted from October 18th 2015 to December 2018, allowing for a washout period of 4 months. Data collection All data were retrieved from our patient data management system (Metavision; IMDsoft, Tel Aviv, Israel). The following outcomes were noted: mortality, ROP, BPD, NEC, culture proven sepsis, intraventricular haemorrhage (IVH), PVL, and length of NICU stay. The duration of respiratory therapy and supplemental oxygen (measured fraction of inspiratory oxygen above 0.21) was calculated from our patient data management system which routinely samples clinical parameters and ventilator settings once per minute. Mortality until one month after corrected term age was noted. The ophthalmologists in our hospital implemented the Early Treatment of Retinopathy of Prematurity study (ETROP) classification for findings of retinal examination in 2013 and ROP was defined according to this classification.21, 22 When retinal findings were described otherwise, researcher NJO classified according to the ETROP criteria retrospectively, assisted by an ophthalmologist where necessary. An assessment for BPD was made at 36 weeks postmenstrual age, using where necessary discharge papers from regional hospitals and classified as mild, moderate, or severe according to criteria from the 2000-NICHD consensus. 23 NEC was defined