Oxygen therapy in the pre-hospital setting for sudden worsening of chronic obstructive pulmonary disease

Background

Chronic obstructive pulmonary disease (COPD) is a chronic condition characterised by progressively worsening reduction of airflow through the lungs. People with COPD are prone to sudden episodes where their symptoms become worse (e.g. persistent increase in shortness of breath and changes in mucous volume and consistency) and oxygen levels may fall. Initial treatment during these episodes, when patients are being transported to hospital, usually includes oxygen. However, delivering too much oxygen to these patients may cause a rise in the level of carbon dioxide that can eventually lead to a reduced breathing rate and possibly stop their ability to breathe at all.

Review question

This review aimed to investigate if oxygen therapy delivered at different concentrations based on patient needs would be less harmful, more harmful, or make no difference when compared to a control group using high-flow oxygen.

Study characteristics

To investigate this question we looked for randomised controlled trials (RCTs), these are studies in which people involved have an equal chance of receiving the treatment or comparator. We were interested in trials that compared different flow rates (concentrations) of oxygen delivered in an ambulance to people being transferred to hospital because of sudden worsening of COPD symptoms.

Key results

Only one study was found that addressed the review question. The study randomised participants to either have titrated oxygen (oxygen therapy delivered at different concentrations tailored to patient needs in order to keep the levels of oxygen in the blood between 88% and 92%) or high-flow oxygen (oxygen therapy delivered at a consistently high concentration).

There were fewer deaths (two people) in the group that received titrated oxygen, compared to the control group using high-flow oxygen delivered at eight to ten litres per minute using a mask (11 people).

Certainty of evidence

Due to inclusion of only one study, and the small number of deaths that occurred, our confidence in the size of the difference between the two treatments is limited. We judged the evidence to be of low certainty.

Bottom line

The one included study found that delivering individually tailored oxygen concentrations to people when they are being transported to hospital with sudden worsening of COPD, reduces the risk of death compared to using a consistently high concentration of oxygen. However, the body of evidence is too small to confidently claim that titrated oxygen is less harmful and more effective than high-flow oxygen in this group of people across the board.

This plain language summary is current to September 2019.

Authors' conclusions: 

The one included study found a reduction in pre/in-hospital mortality for the titrated oxygen arm compared to the high-flow control arm. However, the paucity of evidence somewhat limits the reliability of these findings and generalisability to other settings. There is a need for robust, well-designed RCTs to further investigate the effect of oxygen therapies in the pre-hospital setting for people with AECOPD.

Read the full abstract...
Background: 

Chronic obstructive pulmonary disease (COPD) is a global leading cause of morbidity and mortality, characterised by acute deterioration in symptoms. During these exacerbations, people are prone to developing alveolar hypoventilation, which may be partly caused by the administration of high inspired oxygen concentrations.

Objectives: 

To determine the effect of different inspired oxygen concentrations ("high flow" compared to "controlled") in the pre-hospital setting (prior to casualty/emergency department) on outcomes for people with acute exacerbations of COPD (AECOPD).

Search strategy: 

The Cochrane Airways Group Specialised Register, reference lists of articles and online clinical trial databases were searched. Authors of identified randomised controlled trials (RCTs) were also contacted for details of other relevant published and unpublished studies. The most recent search was conducted on 16 September 2019.

Selection criteria: 

We included RCTs comparing oxygen therapy at different concentrations or oxygen therapy versus placebo in the pre-hospital setting for treatment of AECOPD.

Data collection and analysis: 

Two review authors independently assessed trial quality and extracted data. The primary outcome was all-cause and respiratory-related mortality.

Main results: 

The search identified a total of 824 citations; one study was identified for inclusion and two studies are awaiting classification. The 214 participants involved in the included study were adults with AECOPD, receiving treatment by paramedics en route to hospital. The mean age of participants was 68 years.

A reduction in pre/in-hospital mortality was observed in favour of the titrated oxygen group (two deaths in the titrated oxygen group compared to 11 deaths in the high-flow control arm; risk ratio (RR) 0.22, 95% confidence interval (CI) 0.05 to 0.97; 214 participants). This translates to an absolute effect of 94 per 1000 (high-flow oxygen) compared to 21 per 1000 (titrated oxygen), and a number needed to treat for an additional beneficial outcome (NNTB) of 14 (95% CI 12 to 355) with titrated oxygen therapy. Other than mortality, no other adverse events were reported in the included study.

Wide confidence intervals were observed between groups for arterial blood gas (though this may be confounded by protocol infidelity in the included study for this outcome measure), treatment failure requiring invasive or non-invasive ventilation or hospital utilisation. No data were reported for quality of life, lung function or dyspnoea. Risk of bias within the included study was largely unclear, though there was high risk of bias in domains relating to performance and attrition bias. We judged the evidence to be of low certainty, according to GRADE criteria.

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