1. Department of Anesthesiology, The Third Hospital of Hebei Medical University, Shijiazhuang, Hebei 050051, P.R. China
2. Department of Anesthesiology, Hebei Chest Hospital, Shijiazhuang, Hebei 050051, P.R. China
3. Department of Orthopaedic Surgery, The Third Hospital of Hebei Medical University, Shijiazhuang, Hebei 050051, P.R. China