Hai Hu1, Xinmiao Du2, Yarong He3, Cao Yu3. 1. Department of Emergency Medicine, West China Hospital, Sichuan University, Sichuan, PR China. Electronic address: whowasyoung@126.com. 2. Respiratory and Critical Care Medicine Department, West China Hospital, Sichuan University, PR China. 3. Department of Emergency Medicine, West China Hospital, Sichuan University, Sichuan, PR China.