A 75-year-old man presents with a 1-week history of progressive abdominal distention and a 2-day history of obstipation. He is afebrile and his vital signs are within normal limits. On examination, he has massive abdominal distention and there is tympany to percussion, but no signs of peritonitis. Computed tomography reveals a large bowel obstruction with a whirl sign on the left side of the abdomen. There are no signs of bowel ischemia or perforation. What is the best next step in management?