Definition of respiratory support need
The respiratory needs in our study included hood oxygen support, CPAP, mechanical ventilation (MV) and PS. In this study, we defined ”hood oxygen support need” as over 6 hours of support after birth that still did not relieve the infant’s respiratory difficulty. Different from temporary usage, this prolonged hood oxygen support is highly likely a harbinger of severe TTN, RDS or other lung diseases according to our experience. According to our policy, pure oxygen with a pressure of 6 cm H2O was led into a hood that covered the infant’s head completely, so it mixed with ambient air and provided the infant with approximately 30% oxygen and atmospheric pressure. CPAP was applied when hood oxygen support could not stabilize the infant’s oxygen saturation, or when severe lung diseases were confirmed by chest X-ray. CPAP using a mask with a starting pressure of approximately 6-8 cm H2O and positive end-expiratory pressure (PEEP) was individualized depending on clinical condition, oxygenation and perfusion. MV was used in infants with RDS or when other methods of respiratory support failed. PS use depends on a combination of clinical evidence (e.g., FiO2 to maintain normal saturations, work of breathing) and appearance on chest X-ray. Usually, FiO2 >0.30 in infants on CPAP is regarded as the threshold22. All infants received respiratory support and were later confirmed to have certain lung diseases, and the diagnosis was made according to the integration of evidence from prenatal and postnatal clinical data (such as GA, inflammatory markers, microbiological test results, and physical examination findings) and X-ray images (RDS22-23, TTN24, pneumonia23, MAS25).