Protective measures during tracheostomy for patients with novel coronavirus pneumonia report of 4 cases Zhonghua Er Bi Yan Hou Tou Jing Wai Ke Za Zhi 2020 Dec 07 55 12 1172 1174 Authors He LC Sun YQ Wang YS Wang SJ Wang SC Fan YP Zhang D PMID 33342135 PubMed as supplied by publisher