Review question
We reviewed the evidence regarding effects of oxygen compared with air on breathlessness in people with chronic obstructive pulmonary disease (COPD) with only mildly or moderately decreased blood oxygen levels.
Background
People with COPD are sometimes prescribed oxygen therapy to reduce the severity of breathlessness. However, the use of oxygen in people who do not have severely reduced levels of oxygen in their bloodstream remains controversial, as little is known about its effectiveness. Additionally, oxygen is relatively costly and is not given without risk, particularly to smokers because of the risk of fire.
Study characteristics
We examined the research published to 12 July 2016. We included studies of oxygen therapy versus air delivered through nasal prongs or mask during exertion, continuously, 'as needed' over a defined period or as short-burst oxygen before exertion. Study participants were 18 years of age or older, had received a diagnosis of COPD, had low oxygen levels in the blood and did not receive long-term oxygen therapy. We included a total of 44 studies (1195 participants) in this review. Compared with the previous review, which was published in 2011, we have added 14 studies (493 participants) to this review.
Key results
We found that oxygen can modestly reduce breathlessness. To be effective, oxygen has to be given during exercise. Most studies evaluated oxygen given during exercise testing in the laboratory. Oxygen therapy during daily life had uncertain effects on breathlessness and did not clearly change patient quality of life.
Quality of the evidence
We rated the quality of evidence using one of the following grades: very low, low, moderate or high. For very low-quality evidence, we were uncertain about the results. With high-quality evidence, we were very certain about the results. We found that evidence for oxygen given for breathlessness was moderate to low. We are moderately confident that oxygen can relieve breathlessness when given during exercise to people with COPD with mildly or moderately decreased blood oxygen levels. However, most studies reported acute effects during an exercise test, and no evidence suggests that oxygen decreases breathlessness during daily life. Findings indicate that oxygen does not affect health-related quality of life.
We are moderately confident that oxygen can relieve breathlessness when given during exercise to mildly hypoxaemic and non-hypoxaemic people with chronic obstructive pulmonary disease who would not otherwise qualify for home oxygen therapy. Most evidence pertains to acute effects during exercise tests, and no evidence indicates that oxygen decreases breathlessness in the daily life setting. Findings show that oxygen does not affect health-related quality of life.
Breathlessness is a cardinal symptom of chronic obstructive pulmonary disease (COPD). Long-term oxygen therapy (LTOT) is given to improve survival time in people with COPD and severe chronic hypoxaemia at rest. The efficacy of oxygen therapy for breathlessness and health-related quality of life (HRQOL) in people with COPD and mild or no hypoxaemia who do not meet the criteria for LTOT has not been established.
To determine the efficacy of oxygen versus air in mildly hypoxaemic or non-hypoxaemic patients with COPD in terms of (1) breathlessness; (2) HRQOL; (3) patient preference whether to continue therapy; and (4) oxygen-related adverse events.
We searched the Cochrane Airways Group Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and Embase, to 12 July 2016, for randomised controlled trials (RCTs). We handsearched the reference lists of included articles.
We included RCTs of the effects of non-invasive oxygen versus air on breathlessness, HRQOL or patient preference to continue therapy among people with COPD and mild or no hypoxaemia (partial pressure of oxygen (PaO2) > 7.3 kPa) who were not already receiving LTOT. Two review authors independently assessed articles for inclusion in the review.
Two review authors independently collected and analysed data. We assessed risk of bias by using the Cochrane 'Risk of bias tool'. We pooled effects recorded on different scales as standardised mean differences (SMDs) with 95% confidence intervals (CIs) using random-effects models. Lower SMDs indicated decreased breathlessness and reduced HRQOL. We performed subanalyses and sensitivity analyses and assessed the quality of evidence according to the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) approach.
Compared with the previous review, which was published in 2011, we included 14 additional studies (493 participants), excluded one study and included data for meta-analysis of HRQOL. In total, we included in this review 44 studies including 1195 participants, and we included 33 of these (901 participants)in the meta-analysis.
We found that breathlessness during exercise or daily activities was reduced by oxygen compared with air (32 studies; 865 participants; SMD -0.31, 95% CI -0.43 to -0.20; I2 = 29%; low-quality evidence). This translates to a decrease in breathlessness of about 0.7 points on a 0 to 10 numerical rating scale. In contrast, we found no effect of short-burst oxygen given before exercise (four studies; 90 participants; SMD -0.03, 95% CI -0.28 to 0.22; I2 = 0%; low-quality evidence). Oxygen reduced breathlessness measured during exercise tests (30 studies; 591 participants; SMD -0.34, 95% CI -0.46 to -0.22; I2 = 29%; moderate-quality evidence), whereas evidence of an effect on breathlessness measured in daily life was limited (two studies; 274 participants; SMD -0.13, 95% CI, -0.37 to 0.11; I2 = 0%; low-quality evidence).
Oxygen did not clearly affect HRQOL (five studies; 267 participants; SMD 0.12, 95% CI -0.04 to 0.28; I2 = 0%; low-quality evidence). Patient preference and adverse events could not be analysed owing to insufficient data.