A 4-Hour-Old Male Newborn Has Perioral Discoloration for the Past

A 4-hour-old male newborn has perioral discoloration for the past several minutes. Oxygen by nasal cannula does not improve the cyanosis. The newborn's temperature is 37.1°C (98.8°F) , pulse is 170/min, respirations are 55/min, and blood pressure is 80/60 mm Hg. Pulse oximetry shows an oxygen saturation of 85%. Cardiopulmonary examination shows a 2/6 holosystolic murmur along the lower left sternal border. The abdomen is soft and non-tender. Peripheral pulses are normal.  A chest radiograph reveals clear lungs and a normal cardiac silhouette but a narrowed mediastinal shadow.  Which of the following is the most likely cause of cyanosis in this patient?

A) Impaired alveolar-capillary diffusion
B) Impaired left ventricular contractility
C) Inability of hemoglobin to bind oxygen
D) Right-to-left cardiac shunting
E) Ventilation-perfusion mismatch

Correct Answer:

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