Interstitial lung diseases (ILDs) are characterized by scarring of lung tissue. Stiffening of the lungs leads to reduced transfer of oxygen into the blood, decreased exercise capacity and premature death. Around 85% of the ILDs are known as fibrotic ILD (fILD), a form of ILD which tends to have worse outcomes than other types of ILD. People with fibrotic ILD often experience distressing breathlessness, cough and fatigue; loss of independence and life roles; financial strain; and unpleasant treatment side effects.The most common of the fILDs is idiopathic pulmonary fibrosis (IPF), which has an average survival of 3 years from diagnosis. Recently, two new treatments have been shown to halve the annual decline in lung function in mild to moderate IPF, making it a 'treatable' condition for the first time. However, these treatments only slow the decline in lung function; they do not stabilize or reverse it, nor do patients experience improved quality of life or breathlessness.

For people with fILD who have abnormally low oxygen in the blood at rest, long term oxygen therapy (LTOT, used ≥18 hours per day) is strongly recommended, based on survival benefits in studies of people with chronic obstructive pulmonary disease (COPD). However, for people with fILD who have low oxygen levels only during exertion, the role of oxygen therapy is not clear.

Ambulatory oxygen therapy (AOT), defined as the use of oxygen during exercise and activities of daily living, has historically been used to improve blood oxygen levels and exercise capacity. However, many people with fILD find this treatment difficult to use. Oxygen cylinders are heavy and run out quickly, therefore patient burden often exceeds any benefits. Portable oxygen concentrators (POCs) are newly available, lighter and rechargeable. However there are potential disadvantages to POCs. Generally, they deliver oxygen in pulses, which is where oxygen is delivered only when breathing in, and they do not deliver 100% oxygen. Doctors often express concerns that POCs cannot meet the demands of people with fILD during exercise. Recently it was shown that people with fILD who use a POC have similar blood oxygen levels to those who use a cylinder during exercise, suggesting that this might be a useful treatment.

This study will examine the benefits and costs of ambulatory oxygen, delivered using a POC, in people with fILD and exertional desaturation. The aim is to compare the impact of AOT vs air in people with fILD who have low blood oxygen during exercise, and to compare the cost-effectiveness of AOT and air in fILD. A total of 260 people with fILD will be invited to participate. The trial will be conducted at four sites in Australia and two sites in Sweden. Participants will be randomly allocated into two groups; Group 1 will be administered AOT using a POC (AOT group); and Group 2 will be administered sham AOT using an identical POC (air group). Participants, health professionals and trial staff will not be aware of which POC is being used. The allocated treatment will be delivered for 6 months. Measurements of physical activity during daily life, symptoms, exercise capacity and HRQOL will be collected at the beginning of the trial, and 3 and 6 months after treatment has commenced. Information about use of health care services, both from hospital records and directly from participants will also be collected.