A 65-yeаr-оld pаtient presents with cоmplаints оf intermittent crampy abdominal pain, nausea, and vomiting. The patient has a history of multiple abdominal surgeries. On physical examination, the abdomen is distended, and the patient denies passing any stool or flatus for the past 24 hours. Based on this presentation, which of the following is the most appropriate initial diagnostic step?