Key learning points
- Long-term oxygen therapy is used for many patients with chronic stable hypoxaemia
- Studies suggest a relationship between survival and average daily duration of oxygen use
- Oxygen is not recommended for patients who are breathless but not hypoxic
Long-term oxygen therapy (LTOT) is a well-established therapy for many patients with chronic stable hypoxaemia. There are deficits in our knowledge regarding mechanisms of action, indications for prescription and effects on patient outcomes. This article discusses the role of LTOT and the evidence we have for its use.
A review of the evidence
What we know about LTOT derives mainly from studies in chronic obstructive pulmonary disease (COPD), although patients with other causes of chronic hypoxaemia and its consequences are also likely to benefit.
Early studies in LTOT included the Medical Research Council (MRC) and Nocturnal Oxygen Therapy Trial Group (NOTT) trials.1,2 The MRC trial investigated 87 patients randomised to two groups, reporting a survival benefit in hypoxic patients with COPD receiving oxygen therapy compared with controls who did not receive supplemental oxygen.1 Among men, it took 500 days for this survival benefit to be observed, while there were too few women included for any specific subgroup analyses of women to be conducted.1
The NOTT study compared two different oxygen delivery methods: continuous oxygen and 12-hour nocturnal oxygen therapy.2 The study reported that the mortality rate was almost two times higher for patients receiving nocturnal oxygen compared with those receiving continuous oxygen.2
Together, these studies suggest improved survival among patients receiving 12 to 15 hours of LTOT, indicating a relationship between survival and average daily duration of oxygen use.1,2 Meanwhile, any differences in survival that are observed may be related to the duration of oxygen therapy, the method used, or both.
Since the publication of these early trials, several uncontrolled studies have been conducted, which have obtained findings that are broadly consistent with these data.3,4 Such studies have also identified factors that independently reduce survival in patients receiving LTOT, including increasing age and the presence of chest wall abnormalities.5
In contrast with the NOTT and MRC studies, subsequent trials have reported no effect of LTOT on survival.6,7 However, these studies included participants with moderate rather than severe resting hypoxaemia, suggesting that individuals with less severe COPD do not, as a group, derive any survival benefit from LTOT.
Pragmatically, we tend to prescribe LTOT for 15–16 hours a day, allowing some time off oxygen in which patients can continue with their life. Moreover, if an individual goes out of the home or desaturates on exercise, ambulatory oxygen can be prescribed.8
Many patients with severe COPD continue to smoke and it remains unclear whether LTOT is efficacious for current smokers. There are also risks of burns if people smoke while using oxygen because of oxygen’s ability to enhance the combustion of an existing fire. Unfortunately, burns and deaths due to smoking while on oxygen continue to occur.9
If a patient with advanced disease is breathless and hypoxic, oxygen is the preferred treatment. However, palliative oxygen therapy is not recommended for patients who are breathless and not hypoxic, and other interventions such as fan therapy should be considered.10 Therefore, LTOT provides a treatment option for severe COPD, but only for appropriate patients.
For information on prescribing LTOT see the article by Jane Scullion on Prescribing long-term oxygen therapy
Jane Scullion, respiratory nurse consultant, University Hospitals of Leicester, and a respiratory clinical lead within the East Midlands working with the Clinical Senate
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