The goal of this clinical trial is to compare the effectiveness of two airway clearance techniques for patients with ventilator associated pneumonia. The main questions it aim to answer are:

• effect of the therapies on volume changes
• outcome on sputum clearance Participants will receive airway clearance techniques of
• chest physiotherapy
• high frequency chest wall oscillation.

Sputum can be accumulated in the airways of intubated patients, resulting in recurrent pneumonia. The airway clearance therapy is often utilized with chest physiotherapy or high frequency chest wall oscillation which has become popular for its easy of use and less time consuming to the healthcare workers. The main questions it aim to answer are on effectiveness of the therapies on lung volume changes and sputum clearance by two airway clearance techniques. With the oscillation of entire chest wall, the investigators hypothesize that the high frequency chest wall oscillation is more effectively clear sputum in the distal airways.

Inclusion Criteria:

• Diagnosed with chronic pulmonary disease
• Diagnosed with ventilator associated pneumonia
• Receive airway clearance therapy

Exclusion Criteria:

• Head injury, spinal injury
• Instable hemodynamics
• Intercranial pressure > 20 cmH2O
• Active hemoptysis
• Empyema
• Eye surgery
• Abdominal distension
• Chest tube insertion
• Active tuberculosis

The group will be coded and masked to the investigator and the outcome accessor.