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This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.

There was no benefit to routinely giving oxygen to people who have had a stroke. Oxygen given continuously, or just overnight, did not reduce disability or death and it did not improve people’s ability to do everyday tasks or live independently. There were no oxygen-related adverse events reported.

Strokes occur when the blood supply to the brain is disrupted by either a blocked or burst blood vessel. They can lead to death or disability as parts of the brain are deprived of blood. Therefore, giving oxygen to reduce the potential damage may appear to make sense.

Guidelines from NICE and the British Thoracic Society recommend that people are not routinely given oxygen after a stroke unless their oxygen levels drop. This large NIHR funded trial provides evidence to support these recommendations and reinforces the need to monitor oxygen levels to guide the appropriate use of oxygen therapy on an individual basis. Given the size and quality of this UK-based trial, it is unlikely that future research would change these recommendations.

Why was this study needed?

A stroke is when the brain is deprived of blood, either due to a blocked blood vessel (the commonest form) or a bleed (less common). There are over 100,000 strokes annually in the UK.

The reduced flow of blood and oxygen can lead to areas of the brain being damaged or dying. Stroke treatment is improving, and twice as many people survive strokes now than they did in 1990. However, around two-thirds of stroke survivors are left with a long-term disability.

Giving oxygen to people who have had a stroke could plausibly help to prevent or reduce brain damage. However, high levels of oxygen can also be harmful – causing constriction of the blood vessels, reduced blood flow to the brain, damage to the lungs and restricting people’s mobility.

This trial aimed to provide further clarity about whether routinely offering people low-dose oxygen after a stroke affected a range of outcomes important to patients.

What did this study do?

The UK-based SO2S randomised controlled trial equally allocated 8,003 adults admitted to hospital after stroke to groups who either received continuous oxygen, night-time oxygen or no routine oxygen (control) within 24 hours. Participants’ oxygen levels were monitored four times a day.

The average age of participants was 72 years, 55% were men, and 92% were living independently before their stroke. Oxygen was administered before hospital admission in 20% of people, and the average oxygen saturation was 96.6% at randomisation.

Diagnoses were an ischaemic stroke (82%), haemorrhagic stroke (7%), stroke of unknown type (4%), transient ischaemic attack (2%), non-stroke diagnosis (4%) and missing data (1%).

Around 82% of people managed to take the oxygen in the way intended. The remainder did not, and this was mainly due to confusion and restlessness. Monitoring at 6 am and midnight were introduced halfway through the trial to check this “adherence”.

What did it find?

  • There was no difference in people’s level of disability after 90 days whether they received oxygen or not (adjusted odds ratio [aOR] 0.97, 95% confidence interval [CI] 0.89 to 1.06), and no difference between people who received continuous oxygen or night-time oxygen (aOR 1.01, 95%CI 0.92 to 1.12).
  • The number of people who died was similar in all people who received oxygen compared with those who did not (hazard ratio [HR] 0.97, 99% CI 0.78 to 1.21). There was also no difference between continuous and night-time only oxygen (HR 1.15, 99% CI 0.90 to 1.48).
  • There was no difference between the groups in the number of people at 90 days who were living independently or living in their own home, their ability to perform basic or extended everyday activities, or quality of life. Neurological outcomes after one week were also similar.
  • The number of serious adverse events was similar in all groups, and no oxygen-related adverse events were reported.

What does current guidance say on this issue?

Guidelines by NICE (2008), the Royal College of Physicians (2016) and the British Thoracic Society (2017) recommend giving oxygen to people who have had a stroke if their oxygen levels drop. The accepted threshold at which oxygen is advised is around 95% oxygen saturation. Routine oxygen administration is not recommended.

Oxygen monitoring is advised every four hours day and night. Oxygen should be administered via a tube in the nose, using the lowest concentration possible to restore oxygen levels. Keeping people with existing heart or respiratory conditions sitting upright can help to maintain oxygen levels.

What are the implications?

This trial provides robust UK data that reinforces guideline recommendations to not routinely give additional oxygen to people after they have had a stroke. Rather, people’s oxygen levels should be monitored so that supplemental oxygen can be used when medically necessary.

These findings highlight the need for regular monitoring of oxygen levels for all people who have had a stroke and monitoring of oxygen use to ensure adherence when it is used.

Not using oxygen routinely is likely to save the NHS money and nurse time for use on other things.

Citation and Funding

Roffe C, Nevatte T, Sim J, et al; Stroke Oxygen Study Investigators and the Stroke Oxygen Study Collaborative Group. Effect of Routine Low-Dose Oxygen Supplementation on Death and Disability in Adults With Acute Stroke: The Stroke Oxygen Study Randomized Clinical Trial. JAMA. 2017;318(12):1125-35.

This project was funded by the National Institute for Health Research Health Technology Assessment Programme (project number 09/104/21) and the Research for Patient Benefit Programme.



British Thoracic Society Emergency Oxygen Guideline Development Group. BTS guideline for oxygen use in adults in healthcare and emergency settings. Thorax. 2017;72(suppl 1):256-73.

Intercollegiate stroke working party. National clinical guideline for stroke. London: The Royal College of Physicians; 2016.

NHS website. Stroke. London: Department of Health and Social Care; updated 2016.

NICE. Stroke and transient ischaemic attack in over 16s: diagnosis and initial management. CG68. London: National Institute for Health and Care Excellence; 2008.

Stroke Association. State of the nation: stroke statistics. London: Stroke Association; 2017.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre


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