Review Question - QID 211062

A 5-year-old boy presents to the emergency department with sudden onset nausea and vomiting that started 2 hours ago. The patient's parents can not recall any inciting event and note he suddenly started acting irritable, started vomiting, and experienced 1 episode of diarrhea. His temperature is 98.7°F (37.1°C), blood pressure is 90/50 mmHg, pulse is 160/min, respirations are 29/min, and oxygen saturation is 99% on room air. The patient experiences 1 episode of bloody emesis while in the emergency department. Laboratory values are ordered as seen below.

Serum:
Na+: 140 mEq/L
Cl-: 100 mEq/L
K+: 4.3 mEq/L
HCO3-: 19 mEq/L
Glucose: 99 mg/dL
Creatinine: 1.1 mg/dL
Ca2+: 10.2 mg/dL

Radiography is performed and is notable for radiopaque objects in the gastrointestinal tract. Which of the following is the most appropriate initial step in management?