Approach to growth faltering Quiz: Ace Your Exams

A 1-month-old female infant is evaluated in the clinic during a 1-month-old well check. The infant is breastfed, but the parents note that she tires easily and sweats while feeding. She feeds 8-10 times a day, five minutes on each side, and latches well. There is no history of choking, coughing with feeding, diarrhea, or vomiting. Parents report frequent spit-ups that are nonbloody, nonbilious, not projectile and do not cause the infant discomfort. There is appropriate urine output and 6-8 diapers with stool every day. There is an older sibling at home who attends daycare and is frequently sick. The infant was born at full term with no complications during pregnancy or delivery. At birth, weight, length, and head circumference were at the 30th percentile. Temperature is 37° C (98.6° F), pulse is 180/min, respirations are 45/min, blood pressure is 82/45 mm Hg, and oxygen saturation is 96% on room air. Weight and height are at less than the 5^th percentile. Head circumference is at the 25^th percentile. Physical examination reveals a calm infant in mild respiratory distress. No dysmorphic features are noted. There is tachypnea and faint diffuse crackles are appreciated on lung examination. Cardiac examination reveals a grade 2/6 holosystolic murmur heard best at the left sternal border. No hepatosplenomegaly is appreciated. The patient is sent to the Emergency Department. Which of the following is the best next step in management?