A newborn is noted to have a wide pulse pressure with bounding peripheral pulses and a continuous machinery murmur maximal at the left infraclavicular area. Two days later the infant develops differential cyanosis, with lower limb oxygen saturation lower than upper limb saturation. What is the most likely explanation for this change?

• A Transposition of the great arteries with mixing at the ductal level
• B Coexisting coarctation of the aorta proximal to the ductus
• C Closure of the ductus arteriosus with resultant right-to-left flow across a VSD
• D Reversal of shunt through the ductus due to pulmonary hypertension ✓

Explanation

Differential cyanosis occurs when pulmonary vascular resistance rises and the ductal shunt reverses to right-to-left, delivering desaturated ductal blood into the descending aorta while the head and arms receive oxygenated blood from the proximal aorta. Coarctation proximal to the ductus would cause differential cyanosis of the upper limbs instead, which kills that distractor. Transposition causes general rather than differential cyanosis.

Reference: Nelson Textbook of Pediatrics, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.