A 5-Week-Old Boy with a 1-Week History of Vomiting

A 5-week-old male infant presented with a 1-week history of vomiting. His mother stated that the vomiting generally occurred soon after the infant was fed. Initially, the vomiting was infrequent but was progressively worsening. The patient’s mother reported that the infant had been feeding well and had a good appetite. However, he had begun vomiting the entire volume of formula shortly after being fed since the day prior to this presentation. His mother reported that the vomitus was nonbilious and that there was a decrease in urinary output from 6 to 4 diapers daily. The patient was not febrile, and there was no cough or shortness of breath. History was negative for diarrhea or bloody stool. The infant was born full term via normal spontaneous vaginal delivery. A review of the patient’s past medical and family history was noncontributory. On physical examination, the patient was afebrile with a minimally elevated heart rate. He appeared to be somewhat uncomfortable but was in no acute distress. Mucous membranes were moist, and the lungs were clear on auscultation. The abdomen was moderately distended; on palpation of the abdomen, the infant forcefully vomited and then began to cry. Rectal examination was normal, and the stool was negative for blood. The remainder of the physical examination was normal. An intravenous fluid bolus of 20 mL/kg of normal saline was started, and an abdominal radiograph (Figure 1) and electrolyte panel were ordered (Table).