1. Department of General Surgery, Medical College of Shandong University, Jinan, Shandong 250012, P.R. China
2. Department of Gastroenterology, Binzhou Medical University Hospital, Binzhou, Shandong 256603, P.R. China
3. Department of Anesthesiology, Binzhou Medical University Hospital, Binzhou, Shandong 256603, P.R. China
4. Department of General Surgery, Binzhou Medical University Hospital, Binzhou, Shandong 256603, P.R. China