A 63-year-old man is brought to the emergency department due to 4 days of progressively worsening, diffuse, crampy abdominal pain rated 6/10. He reports nausea and 2 episodes of vomiting today; his last bowel movement was 3 days ago. Medical history is significant for hypertension, recurrent constipation, and an emergency laparotomy 5 years ago for a perforated duodenal ulcer. His father died of colorectal cancer at age 65. The patient smokes 1 pack of cigarettes daily and takes lisinopril and lactulose. Temperature is 37.6°C (99.7°F), pulse is 89/min, and blood pressure is 120/80 mm Hg. Abdominal examination reveals distention and mild diffuse tenderness without guarding or rebound. Bowel sounds are high-pitched. Digital rectal examination is unremarkable. An abdominal x-ray is shown. In addition to fluid resuscitation, which of the following is the most appropriate next step in management for this patient?