A 68-year-old man presents to the emergency department with acute onset severe abdominal pain and abdominal distension for 6 hours. He has a history of previous abdominal surgery 15 years ago. On examination, he is afebrile, blood pressure 130/85 mmHg, heart rate 102/min, and the abdomen is distended with hyperactive bowel sounds. Plain abdominal radiograph shows multiple dilated small bowel loops (>3 cm diameter) with air-fluid levels in a stepladder pattern, and collapsed distal small bowel. What is the most likely diagnosis?