All of the eligible patients had acute pneumonic respiratory failure and received endotracheal intubation and mechanical ventilation, and all signed informed consent forms. The patients were randomly allocated to the study group (HFCWO) or the control group (CCPT), as the efficacy of bronchial hygiene for both HFCWO and CCPT is comparable4. The primary investigators were blinded to which procedure the patients received. The local institutional review board of Chung Shan Medical University Hospital approved this study (No. CS13004). The experimental research was conducted in compliance with the Helsinki Declaration.