The Stroke Oxygen Study (SO2S): A multi-centre, prospective, randomised, open, blinded-endpoint study to assess whether routine oxygen supplementation (ROS) in the first 72 hours after a stroke improves long-term outcome

Approximately 110,000 strokes occur in England every year and it is the third largest cause of mortality. 33,000 are significantly disabled, making it the single largest cause of adult disability, about 50% of stroke survivors are dependent on others for everyday activities. Stroke costs the NHS and the economy approximately £7 billion a year of which £2.8 billion are direct costs, £2.4 billion are care costs and £1.8 billion in income loss due to lost productivity and disability. Hypoxia is common early after acute stroke and is associated with worse outcome. About 60% of stroke patients will have at least one episode of hypoxia in the first 48 hours. Even amongst stroke patients who are normoxic on screening during the day 23% develop hypoxia at night. Routine oxygen supplementation could prevent hypoxia and related brain damage. However, there is some evidence from preclinical studies that hyperoxia may be neurotoxic, and a small clinical study of short-term fixed-dose oxygen supplementation did not show overall benefit. Appropriate management of post stroke hypoxia could prevent deterioration and improve recovery. A survey of British Stroke Physicians shows that there is uncertainty about when and how to treat hypoxia after stroke. European Stroke guidelines and the American Stroke Association suggest maintaining oxygen saturation levels at 92% or above and the UK Royal College of Physicians Guidelines state to keep oxygen saturation at or above 95%. Since there is no evidence from clinical trials to support any of the recommendations, it is not surprising that there are differences. This research will provide the clinical data to support the development of evidence-based guidelines and protocols for the prevention and treatment of hypoxia after stroke. This could be incorporated into the recommended minimal procedural data set which underpins care pathways implemented in stroke units as recommended by NICE.