- Click here for explanation of classification scheme.

To determine the efficacy of ambulatory oxygen in patients with COPD using single assessment studies.

• Only randomized controlled trials were included
• Adult patients with stable COPD
• COPD should have been diagnosed according to internationally accepted guidelines
• Single assessment studies on COPD patients which compare performance during an exercise test using oxygen with performance during an exercise test using placebo air
• Ambulatory oxygen is defined as the use of supplemental oxygen during exercise and activities of daily living

• Patients who did not have a diagnosis of COPD
• Longer term studies assessing the efficacy of ambulatory oxygen therapy or studies assessing the efficacy of long-term oxygen therapy

Recruitment

Cochrane Airways Group COPD register was searched with predefined search terms - (portable* or ambulat* or oxygen* or O₂ or hypoxaemia* or hypoxemia*) and (therap*), as well as other electronically available databases such as CENTRAL.  Bibliographies were also reviewed.  Searches were current as of March 2005.

Design:  Systematic Review 

Blinding used (if applicable):  Studies did not have to be blinded.

Intervention (if applicable):  Both authors extracted and entered data into RevMan 4.2. 

Statistical Analysis

• All trial data was combined using RevMan analyses 1.0.2.
• Funnel plots were carried out to test for the presence of publication bias where possible
• Due to crossover design of the studies, data was entered as generic inverse variance data
• For continuous variables such as exercise capacity and breathlessness scores, a weighted mean difference was used
• Random and/or fixed effects models were used depending on the level of statistical heterogeneity observed

Timing of Measurements

Studies had to compare oxygen and placebo when administered to people with COPD who were undergoing an exercise test.

Dependent Variables

• Exercise capacity (distance, time or steps during maximal tests or endurance tests) 
• Dyspnea scores (through Borg scores or visual analog scale)
• Arterial oxygen saturation - SaO₂
• Physiological measurements such as V_E during exercise 
• Patient preference

Independent Variables

• Oxygen or placebo

Control Variables

 

Initial N: 60 studies were identified through the literature search.  31 studies, contributing 33 data sets, randomizing 534 participants met the inclusion criteria

Attrition (final N):  as above

Age:  mean age reported in included studies ranged from 47 to 73 years

Ethnicity:  not mentioned

Other relevant demographics:  sample sizes ranged from 5 to 41

Anthropometrics:  all trials were crossover in design

Location:   Worldwide studies

 

Other Findings

Oxygen improved all pooled outcomes relating to endurance exercise capacity (distance, time, number of steps) and maximal exercise capacity (exercise time and work rate).

Data relating to VO_2max could not be pooled and results from the original studies were not consistent.

For the secondary outcomes of breathlessness, SaO₂ and VE, comparisons were made at isotime.

In all studies except 2, the isotime is defined as the time at which the placebo test ended.

Oxygen improved breathlessness, SaO₂/PaO₂ and VE at isotime with endurance exercise testing.

There was no data on breathlessness at isotime with maximal exercise testing.

Oxygen improved SaO₂/PaO₂ and reduced VE at isotime. 

This review provides some evidence from small, single assessment studies that ambulatory oxygen improves exercise performance in people with moderate to severe COPD.  The results of the review may be affected by publication bias, and the small sample sizes in the studies.  Although positive, the findings of the review require replication in larger trials with more distinct subgroups of participants.  Maximal or endurance tests can be used in ambulatory oxygen assessment.  Consideration should be given to the measurement of SaO₂ and breathlessness at isotime as these provide important additional information.  We recommend that these outcomes are included in the assessment for ambulatory oxygen.  Future research needs to establish the level of benefit of ambulatory oxygen in specific subgroups of people with COPD.

Government:

North Ireland Research and Development

• Authors note that the results of the review may be affected by publication bias and small sample sizes in studies.
• Authors also note the lack of statistical heterogeneity in many of the meta-analyses - the studies differed in many ways, such as in the type of exercise test deployed, the method and amount of oxygen, whether participants were known to be able to exercise up to a certain capacity, whether studies were single or double blind, and the severity of the participants recruited to the studies