Definition of respiratory support need
Respiratory need in our study includes hood oxygen support, CPAP, mechanical ventilation(MV) and pulmonary surfactant(PS). In this study, we defined ”hood oxygen support need” as over 6-hour support after birth that still can not relief infants’ respiratory difficulty. Different from temperary usage, this prolonged hood oxygen support is high likely a harbinger of severe TTN, RDS or other lung diseases according to our experience. As our policy, pure oxygen with pressure of 6 cm H2O was lead into a hood covered the head of infants completely, so it mixed with air and provide him/her oxygen of approxmate 30% oxygen with atmospheric pressure. The CPAP applied when hood oxygen support can not stabilize infants’ oxygen saturation, or severe lung diseases were confirmed by chest X-ray. The CPAP using a mask with a starting pressure of about 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 have failed. Pulmonary surfactant 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 a threshold22. All infants received respiratory support were confirmed with certain lung diseases later, and the diagnosis was made according to integrating evidence of prenatal and postnatal clinical data (such as GA, inflammatory markers, microbiological test results, and physical examination findings) and X-ray inspection(RDS22-23,TTN24, pneumonia23, MAS25).
Statistical Analysis
Data were tested for normality with Kolmogorov-Smirnov test and expressed as mean (standard deviation) or median (interquartile range) as appropriate. Receiver operating characteristic (ROC) analysis was used to evaluate the reliability of the LUS to predict all kinds of respiratory support need(comprehensively and respectively). Areas under the curves (AUCs) and cutoff values showing the highest sensitivity were reported. The AUCs were compared using the method by Hanley and McNeil26 .p< .05 was considered statistically significant. Analyses were performed using SPSS version 15.0 (SPSS Inc) and MedCalc version 13.3 (MedCalc bvba) statistical software.