Emergency Department the Second Affi liated Hospital of Zhejiang University School of Medicine Hangzhou 310009 China;
Emergency Department the Second Affi liated Hospital of Zhejiang University School of Medicine Hangzhou 310009 China;
Emergency Department the Second Affi liated Hospital of Zhejiang University School of Medicine Hangzhou 310009 China;
Emergency Department the Second Affi liated Hospital of Zhejiang University School of Medicine Hangzhou 310009 China;
High-flow nasal cannula oxygen; Noninvasive ventilation; Lung ultrasound; Extubation;