A 5-week-old boy is brought to the office by his mother due to vomiting. The mother explains, "Over the past 4 days, my son has been vomiting forcefully right after drinking his formula. He used to spit up after feeding, but it has been getting worse, and now, he seems to throw up everything he eats." The emesis is the color of milk. The patient has had fewer wet diapers today and a single stool yesterday. He was born at 39 weeks gestation after an uncomplicated pregnancy. Newborn metabolic screening was normal. Medical history is notable for switching to formula at age 2 weeks due to low breast milk production. At that time, the patient was at the 25th percentile for length, weight, and head circumference. Today, he is at the 10th percentile for weight, although length and head circumference remain at the 25th percentile. Temperature is 36.7 C (98.1 F) and pulse is 169/min. Physical examination shows an awake, alert, slightly fussy infant. The anterior fontanelle is open and mildly sunken. The lips and mucous membranes are slightly dry. Cardiopulmonary examination shows no abnormalities. The abdomen is soft and nondistended with active bowel sounds, although waves of peristalsis are visible. There is no hepatosplenomegaly or tenderness to palpation. Serum chemistry is pending. The diagnosis is confirmed. Which of the following is the best next step in management of this patient?
A)Administer intravenous fluids
B)Administer oral rehydration solution
C)Immediately perform a pyloromyotomy
D)Place nasogastric tube for bowel rest