This study aims to identify whether the addition of positive expiratory pressure (PEP) mask therapy to standard medical care improves clinically important outcomes in individuals with acute exacerbations of chronic obstructive pulmonary disease. It is hypothesized that those who receive the additional PEP mask therapy will show greater improvements than those who do not.

This study aims to identify whether the addition of positive expiratory pressure (PEP) mask therapy to standard medical care improves symptoms, quality of life and risk of re-exacerbation in individuals with acute exacerbations of chronic obstructive pulmonary disease.

A PEP mask is a small hand-held device that is self-applied over the nose and mouth. It creates a resistance against exhalation (outward) breaths which helps facilitate movement of sputum from the lungs towards the mouth.

Participants will be recruited from two tertiary metropolitan hospitals in Melbourne, Australia and randomised to receive either 'usual care' (comprising medical management, non-invasive ventilation if required, rehabilitation and allied health interventions) or 'usual care' plus PEP mask therapy for the duration of their hospital admission. All participants will then complete daily diaries for six months after discharge.

The effect of PEP mask therapy will be evaluated using a range of outcomes important to both patients and health care providers.

Inclusion Criteria (all of the following criteria must be met):

• The primary reason for hospital admission is an acute exacerbation of clinically diagnosed COPD
• There is evidence of sputum expectoration or they are a chronic sputum producer ('regularly expectorates sputum on most days')
• They are able and willing to provide written, informed consent
• Recent (within the last 6 months) lung function data indicates obstructive lung disease (of any severity), according to the GOLD criteria: post-bronchodilator FEV1/FVC < 0.7 (only if available)
• They have a smoking history of ≥ 10 pack/years (only if diagnosis unclear)

Exclusion Criteria (none of the following criteria must be present):

• They are breathing via an artificial airway (e.g. endotracheal or tracheostomy tube)
• They have a more significant respiratory disease other than COPD (e.g. primary diagnosis of bronchiectasis, cystic fibrosis, interstitial lung disease, asthma, lung cancer)
• They have had recent (within the last 6 months) lung volume reduction procedure(s) (e.g. surgery, valve or stent insertion, or other), lung transplantation or pneumonectomy
• The intervention is contraindicated (including but not limited to evidence of undrained pneumothorax, significant frank haemoptysis, recent facial, oral, oesophageal or skull surgery/trauma, altered conscious state or inability to co-operate)
• They have poor oxygen saturation at rest (SpO2 < 88%) despite supplemental oxygen delivered via nasal prongs
• They intend to continue performing established ACT routines throughout the study period
• It is more than 48 hours since being admitted as an inpatient to hospital.