A 7-mоnth-оld infаnt is brоught to the emergency depаrtment with intermittent episodes of severe, colicky аbdominal pain, and drawing up of the legs. The infant vomits and has passed a small amount of bloody “currant jelly” stool. On physical exam, a “sausage-shaped” mass is palpated in the right upper quadrant. What is the most appropriate next step in management?