A 3-DAY-OLD infant boy was admitted to the neonatal intensive care unit with a history of persistent tachypnea. He was the 2500-g product of a 37-week gestation and normal vaginal delivery. Apgar scores were 8 and 9 at 1 and 5 minutes, respectively. At the referring hospital, his respiratory rate was 120/min and the oxygen saturation was 85% in room air. Supplemental oxygen was given, a blood culture was obtained, and intravenous treatment with ampicillin sodium and gentamicin sulfate was begun. The initial chest radiograph showed perihilar density and fluid in the transverse fissure that was thought to represent transient tachypnea. The blood culture results were negative for organisms after 72 hours and the antibiotic treatment was discontinued. The infant continued to breathe room air but was tachypneic.
On his arrival in the intensive care nursery, his respiratory rate was 110/min and arterial oxygen saturation was normal. Growth parameters, temperature,