You are evaluating a 3-week-old infant with vomiting for the past 3 hours. The mother states that he has been doing well with his cow's milk based formula until 3 hours ago. The vomitus was described as undigested milk mixed with green material. The diagnostic workup of choice for this infant is:
Emergent abdominal ultrasound.
Emergent barium enema.
Emergency upper GI series.
CBC and lipase levels.
Change his diet to a protein hydrolysate formula.
Bilious vomiting in the neonatal period always necessitates an emergent evaluation since 20% of these infants will require surgical intervention. Conditions that present with bilious vomiting in this age group are malrotation with or without a midgut volvulus, annular pancreas, duodenal and jejunal atresia, mecomium ileus, and Hirschsprung disease. Malrotation with midgut volvulus is the most life threatening of these causes and is a surgical emergency. Approximately 50% of cases present in the first month of life. Barium enema is not as reliable as an upper GI series in diagnosing malrotation. It is most useful in evaluating distal bowel obstruction such as Hirschsprung disease. Abdominal ultrasound is useful in diagnosing pyloric stenosis. A CBC and lipase levels are not helpful in making the definitive diagnosis. Changing the formula in an infant who is vomiting bile is not indicated.