Department of Respiratory and Critical Care Medicine The Affiliated Hospital of Qingdao University Qingdao 266003 Shandong Province China;
Department of Hematology The Eighth Medical Center General Hospital of Chinese PLA Beijing 100091 China;
Operation Room The Fourth People’s Hospital of Jinan Jinan 250031 Shandong Province China;
Department of Gynecology and Pediatrics PLA Rocket Force Characteristic Medical Center Beijing 100088 China;
Department of Cardiovascular Surgery The Affiliated Yantai Yuhuangding Hospital of Qingdao University Yantai 264000 Shandong Province China;
Department of Respiratory and Critical Care Medicine The Affiliated Hospital of Qingdao University Qingdao 266003 Shandong Province China;
Department of Respiratory and Critical Care Medicine Jinan Central Hospital Jinan 250013 Shandong Province China;
Refined care; Chronic obstructive pulmonary disease; Acute exacerbation period; Difficulty in expectoration;