PANCE Practice Test 14

A 14-month-old girl is brought to the emergency department because of episodes of inconsolable crying every 15 to 20 minutes for 8 hours, during which she draws her legs up to her abdomen. Between episodes she is quiet and pale. She has vomited three times and passed one stool containing blood and mucus. Temperature is 37.2°C (99.0°F), pulse 132/min, and blood pressure 92/58 mm Hg. The abdomen is soft without guarding. Ultrasonography shows a target-shaped mass in the right upper quadrant. Which of the following is the most appropriate next step in management?