Clinical respiratory parameters:
Respiratory data were collected for all infants during the first 7 days
of life. Data included mean airway pressure (MAP), fraction of inspired
oxygen (FiO2), arterial blood gas measurements, total
mechanical ventilation days, total oxygen days, and success/failure of
extubation events. Oxygen saturation index (OSI) was calculated on
postnatal days 3 and 7; OSI = MAP x FiO2 x100 / arterial
oxygen saturation 10. We stratified respiratory
severity into mild, moderate, and severe based on OSI of ≤ 2.9, 3.0-6.4,
and ≥6.5, respectively 11.