Safe use of emergency oxygen in chronic respiratory disease

Abstract

There is good evidence that long-term oxygen therapy (LTOT) increases life expectancy in patients with severe hypoxaemic chronic obstructive pulmonary disease (COPD). For this reason, LTOT is the largest category of home oxygen use in adults, often supplemented by ambulatory oxygen to allow patients to mobilize. Many patients with COPD who are not sufficiently hypoxaemic to require LTOT have been advised to use short-burst oxygen therapy in the hope and expectation that it would relieve breathlessness after exertion. Although this is not a medical emergency, it is the commonest nonelective use of oxygen for patients with COPD, and the National Health Service in the United Kingdom spends about 18 million pounds per year on this treatment. Despite the widespread use of shortburst oxygen therapy in the United Kingdom, two systematic reviews have concluded that this form of oxygen use has no proven benefit in non-hypoxaemic patients with COPD, and the most recent (and largest) clinical trial has shown no benefit from short-burst oxygen therapy after exertion for patients with severe COPD, even among patients who desaturate on exertion. The advice in the National Institute for Clinical Excellence COPD guideline is that short-burst oxygen therapy should only be considered for episodes of severe breathlessness in patients with COPD not relieved by other treatments and only if an improvement in breathlessness following therapy has been documented. Patients with COPD of sufficient severity to require LTOT are at risk of acute exacerbations of COPD with worsening hypoxaemia. These patients are especially likely to be vulnerable to type 2 respiratory failure (hypercapnia) if high concentrations of oxygen are given. Hypercapnic respiratory failure can lead to increased risk of requirement for mechanical ventilation and increased risk of death when excessive oxygen is administered. Therefore, it is advisable for patients in this situation to call for medical assistance rather than simply turning up the flow rate of oxygen in the home environment. The British Thoracic Society guideline for emergency oxygen therapy recommends an oxygen saturation target range of 88–92% for most such patients although some patients may require a lower target range based on previous blood gas analysis. Most patients in this situation will require urgent transport to hospital where blood gases can be sampled and controlled oxygen therapy can be given. Patients with prior episodes of hypercapnic respiratory failure may be provided with an oxygen alert card and a personal 24% or 28% Venturi mask to ensure that they are not exposed to the risks of hyperoxic hypercapnia during ambulance transfers to hospital. Patients with severe hypoxaemia associated with hypercapnia and acidosis are likely to require treatment with noninvasive ventilation.