A 2-month-old infant with vomiting, diarrhea, tachypnea, and cyanosis

A 2-month-old female infant is brought to your clinic in a rural area for a routine well-baby checkup. According to the child’s chart, she was delivered 2 weeks early because of maternal toxemia. There was no neonatal distress; her birth weight was 7 pounds and 11 ounces.

Today, the mother states that she has noticed an intermittent bluish discoloration of the baby’s lips, tip of the nose, and ears. Physical examination of the infant is negative for both cardiac murmurs and abnormalities on lung auscultation. A below-average weight gain is noted. Feedings have been 4 ounces of diluted formula every 2 hours. The infant has occasional loose stools. You instruct the parents to increase caloric feedings with vitamin and mineral supplements and to call you immediately if any further episodes of the bluish discoloration are observed.

Approximately 3 weeks later, the baby’s frantic parents call your office; the infant is crying incessantly and has vomiting and profuse diarrhea. When the baby is brought to your clinic a few minutes later, she is afebrile but has tachypnea, cyanosis, and drowsiness. Her blood pressure is 78/30 mm Hg (normal 50th percentile for her age is 80/46 mm Hg), heart rate is 140/min, and respiration rate is 40/min. An ambulance is summoned and 100% oxygen by face mask is administered; however, no improvement in the cyanosis is noted on her arrival at the hospital emergency department.

The examining emergency physician now notes a grade II/VI systolic murmur and central cyanosis, which has not improved despite administration of 100% oxygen for nearly 1 hour. There is no evidence of cardiac failure, atelectasis, pneumonitis, or pneumothorax. Therapy is started, which results in a dramatic resolution of the cyanosis. The infant is discharged on the second hospital day with no evidence of central nervous system hypoxic damage.

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