Oxygen is indicated in patients with low oxygen saturations (< 94%) on air. Recent guidelines from NICE and the British Thoracic Society agree that supplementary oxygen has not been shown to be beneficial to these patients, and may indeed be harmful [5, 12]. In those with no risk of hypercapnic respiratory failure, the target saturation should be 94 - 98%, and in those who are at risk, a target of 88 - 92% is appropriate, until an arterial blood gas is available.