1. Intensive Care Unit, Affiliated Qingdao Municipal Hospital of Qingdao University, Qingdao, Shandong 266071, P.R. China
2. Department of Respiratory Medicine, Zibo First Hospital, Zibo, Shandong 255200, P.R. China
3. Department of Emergency, Affiliated Qingdao Municipal Hospital of Qingdao University, Qingdao, Shandong 266071, P.R. China