220 Thumus Size and its Relationship to the Respiratory Distress Syndrome and Cord Blood Cortisol Level in the Preterm Infants

Abstract

Purpose: Thymic size can be affected by glucocorticoids. Glucocorticoids increase surfactant synthesis in preterm infants. We assessed the hypothesis that fetal lung maturity in preterm infants correlates with thymus size detected at birth on routine chest radiograph. We also searched for a possible relationship between thymus size, respiratory distress syndrome, and the cord blood cortisol level.Methods: The cardiothymic/thoracic ratio within 3 hours after birth and cord blood cortisol level were measured in 42 preterm infants admitted to the neonatal intensive care unit of Seoul National University Children's Hospital from June 2002 to December 2003. Multiple linear regression analysis was done to assess the relationships between cardiothymic/thoracic ratio, perinatal events and cord blood cortisol. The receiver operation characteristic curve analysis was done to evaluate the cardiothymic/thoracic ratio in the prediction of respiratory distress syndrome.Results: 8 infants (19.0%) developed respiratory distress syndrome. The cardiothymic/thoracic ratio positively correlated with birthweight (R=0.416, P=0.044), but not with gestational age. The cardiothymic/thoracic ratio were significantly larger in preterm infants with respiratory distress syndrome than those without respiratory distress syndrome (0.419¡3/4 0.058 versus 0.358¡3/4 0.069, P=0.019). After multiple linear regression, birthweight and respiratory distress syndrome were all independently associated with cardiothymic/thoracic ratio (R2=0.252, P=0.048 for RDS, P=0.012 for birthweight). The cord blood cortisol levels were significantly lower in preterm infants with respiratory distress syndrome than in those without respiratory distress syndrome [median 1.550 microgram/dL(range 0.400–13.600 microgram/dL) versus median 3.450 microgram/dL(range 1.000–18.200 microgram/dL), P=0.016]. The cord blood cortisol levels were negatively correlated with cardiothymic/thoracic ratio (R2=0.212, P=0.002). The cardiothymic/thoracic ratio less than 0.37 identified infants with respiratory distress syndrome with 87.5% sensitivity and 61.8% specificity.Conclusion: The larger thymus at birth can be used to identify respiratory distress syndrome. The lower cord blood cortisol levels may be associated with larger thymus in respiratory distress syndrome.