A Cochrane review included 4 studies with a total of 331 subjects. In the intervention groups, the patients were on long-term (> 2 weeks) ambulatory domiciliary oxygen therapy. In the control groups the patients were given placebo air cylinders. Two studies showed a statistically and clinically significant benefit in favour of the intervention for dyspnoea post exercise. The quality of life domain for all four included studies produced a statistically significant benefit for the subcategories of dyspnoea and fatigue, in favour of the oxygen group (dyspnoea mean difference [MD] 0.28, 95% CI 0.10 to 0.45; fatigue MD 0.17, 95% CI 0.04 to 0.31). No evidence of any effect was reported for survival, and limited benefits were observed for exercise capacity as measured by step test and distance walk test.
Statistically significant effects of oxygen on exercise capacity were found in only one of the studies, a crossover trial involving 9 patients with severe hypoxia at rest. This study reported a reduction in minute ventilation at maximal exercise (WMD -11.00 L/min; 95%CI -17.53 , -4.47L/min) and an increase in PaO2 at rest (WMD 17.00 mmHg; 95%CI 9.13,24.87 L/min) with oxygen therapy when compared to placebo. The other study recruited patients who did not have resting hypoxaemia.Comment: The quality of evidence is downgraded by sparse data, indirectness of evidence, and potential reporting bias.