1. Clinical Medicine Skill Center, Jining Medical University, Jining, Shandong 272067, P.R. China
2. Department of Anesthesiology, Xiangyang No. 1 People's Hospital Affiliated to Hubei University of Medicine, Xiangyang, Hubei 441000, P.R. China
3. Endoscopy Center, Binzhou City Center Hospital, Binzhou, Shandong 251700, P.R. China