Recurrent Vomiting in a 6-year-old Boy

A 6-year-old boy presents to the emergency department (ED) with a 1-day history of nonbilious, nonbloody vomiting occurring every 1 to 2 hours. He was not tolerating oral fluids and had decreased urination for 24 hours before presentation. He has nasal congestion and discharge but no fever, abdominal pain, or diarrhea. The parent denies sick contacts and the possibility of ingestions. Vital signs are notable for tachycardia (heart rate, 114...