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Respiratory problems are common after birth in extremely preterm infants (<28 weeks of gestation), and most of these infants require assisted ventilation until they are sufficiently mature and strong enough to breathe by themselves. However, immature lungs are not meant to be exposed to higher concentrations of oxygen than the very low levels provided in the uterus or to the airway pressure that is provided by ventilators to assist breathing. Such exposure can injure the lungs, and injury may arrest pulmonary development.1 Some extremely preterm infants become oxygen dependent for many weeks and are subsequently subject to the development of bronchopulmonary dysplasia.1
Assisted ventilation has changed substantially since the 1970s, when ventilation delivered through an endotracheal tube predominated.2 Less invasive forms of ventilation, including nasal continuous positive airway pressure (CPAP), have evolved over time and in some medical centers have become the most common means of assisting ventilation after birth. Less invasive ventilation is considered to be “gentler” — easier on the lungs — and therefore potentially less injurious. The introduction of antenatal glucocorticoids3 in the 1970s and exogenous surfactant4 in 1991 has also modified the risk of postnatal lung disease, and fewer infants now have the severe atelectasis caused by a lack of surfactant.
Although assisted ventilation has become less invasive during the past 25 years, it is unclear whether assisted ventilation has been associated with improvements in short-term or long-term respiratory function. The aim of our study was to compare changes in assisted ventilation and oxygen therapy administered during the newborn period and in lung function at 8 years of age in children in Victoria, Australia, whose birth was extremely premature over three distinct periods, all of which followed the introduction of exogenous surfactant into clinical practice. We hypothesized that respiratory outcomes would have improved over time, with less oxygen dependence and improved lung function at 8 years of age.
Methods
Study Population and Oversight
Perinatal care in the state of Victoria has been centralized since the 1970s. There have been only four neonatal intensive care units in the state since that time. These neonatal units have collaborated with governmental data-collection agencies and the statewide transport service since the late 1970s to obtain population-based data on long-term outcomes...