A 74-year-old woman presents to the emergency department with several days of worsening abdominal pain and constipation. She reports that her last bowel movement was 3 days ago and is unsure if she has been passing flatus. Vital signs are within normal limits. Physical examination is notable for a markedly distended abdomen. A barium enema radiograph is shown in Figure A. Which of the following is the best next step in management?