Review Question - QID 216244

A 67-year-old man presents to the emergency room reporting sudden-onset abdominal and back pain that began 3 hours ago. He was eating dinner when he started feeling severe pain in his abdomen that made him lose his appetite. He denies any diarrhea or hematochezia and says the pain is not affected by movement. He has a history of hypertension, hyperlipidemia, and depression. He currently takes amlodipine and atorvastatin and is compliant with his medications. He has a 45-pack-year smoking history, but he does not drink alcohol or use any illicit drugs. His temperature is 98.6°F (37°C), his blood pressure is 110/64 mmHg, pulse is 97/min, and respirations are 15/min. Physical exam is notable for diffuse abdominal tenderness without rigidity or guarding. During evaluation, the patient becomes diaphoretic and pale and reports that he feels fatigued. Repeat blood pressure is 87/50 and pulse is 127. Intravenous fluid boluses are administered. Which of the following is the most likely diagnosis?