Review Question - QID 109243

A 4-week-old boy presents with his parents to the pediatrician for a well-child visit. His mother reports he was eating well until 1 week ago when he began vomiting after breastfeeding. His mother has tried increasing the frequency of feeds and decreasing the amount of each feed, but the vomiting seems to be getting worse. The patient now vomits after every feed. The vomitus looks like breast milk. The patient’s mother is exclusively breastfeeding and would prefer not to switch to formula but worries that the patient is not getting the nutrition he needs. Two weeks ago, the patient was in the 75th percentile for weight and 70th for height. He is now in the 60th percentile for weight and 68th percentile for height. His temperature is 98.2°F (36.8°C), blood pressure is 58/37 mmHg, pulse is 144/min, and respirations are 34/min. On physical exam, the patient has dry mucous membranes. His abdomen is soft and non-distended. Which of the following is the most appropriate next step in management?