A 3800-gram newborn is delivered at 43 weeks’ gestation to a 28-year-old woman (G3P3). Apgar scores at 1 and 5 minutes are 2 and 4, respectively. The newborn’s nails and skin are meconium-stained. He is immediately intubated and mechanically ventilated at FiO2 of 100%. Blood gas analysis shows: pH 7.08, pCO2 33 mmHg, pO2 30 mmHg. Chest x-ray shows no pulmonary infiltrates or cardiomegaly. Transthoracic echocardiography shows normal cardiac anatomy with a right-to-left shunt across the foramen ovale. Which of the following is the most likely explanation for these findings?
Closure of ductus arteriosus
Decreased pulmonary vascular resistance
Failure of pulmonary vasodilation
Increased systemic vascular resistance
Intracardiac left-to-right shunt
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Cut-to-the-chase Answer (0:20):
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HY USMLE Answer (8:19):
