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The Stroke Oxygen Study (SO2S) - a multi-center study to assess whether routine oxygen treatment in the first 72 hours after a stroke improves long-term outcome: study protocol for a randomized controlled trial

Christine Roffe1*, Tracy Nevatte2, Peter Crome3, Richard Gray4, Julius Sim5, Sarah Pountain6, Linda Handy7 and Peter Handy7

Author Affiliations

1 Stroke Research, North Staffordshire Combined Healthcare NHS Trust, Holly Lodge, 62 Queens Road, Stoke on Trent, Staffordshire ST4 7LH, UK

2 Stroke Research, Institute for Science and Technology in Medicine, Keele University, Keele ST5 5BG, UK

3 Primary Care and Population Health, University College London Medical School (Royal Free Campus), Rowland Hill Street, London NW3 2PF, UK

4 Clinical Trial Service Unit, University of Oxford, Roosevelt Drive, Oxford OX3 7LF, UK

5 Health Services Research Unit, Keele University, Keele ST5 5BG, UK

6 Stroke Research, Heart of England NHS Foundation Trust, Birmingham B9 5SS, UK

7 Strokes R Us, High Lane, Stoke on Trent ST6 7DZ, UK

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Trials 2014, 15:99  doi:10.1186/1745-6215-15-99

Published: 31 March 2014



Mild hypoxia is common in stroke patients and may have significant adverse effects on the ischemic brain after stroke. The use of oxygen treatment is rapidly increasing in European stroke units but is not without side effects. It impedes early mobilization, could pose an infection risk, and may encourage the formation of toxic free radicals, leading to further damage to the ischemic brain. In the Stroke Oxygen Pilot Study (2 or 3 L/min for 72 hours) neurological recovery at one week was better in the oxygen group than in controls, and after correction for difference in baseline stroke severity and prognostic factors, there was a trend to better outcome with oxygen at six months. Oxygen was as effective in mild as in severe strokes.

Oxygen saturation is lower at night than during the day, and episodes of oxygen desaturation are common during sleep. Nocturnal oxygen supplementation is likely to reduce the burden of hypoxia without interfering with daytime mobilization and rehabilitation.

Before wider use of oxygen supplementation becomes established it is important to obtain better evidence on which patients benefit from such treatment.


Participants will be randomized to one of three groups: the first will receive continuous oxygen for 72 hours (at a rate of 2 or 3 L/min depending on baseline oxygen saturation), the second group will receive nocturnal oxygen only (at a rate of 2 or 3 L/min depending on baseline oxygen saturation) and the third group will not receive any oxygen (control). A baseline assessment is performed at randomization and a one-week follow-up completed. Outcome data at three, six and twelve months will be obtained via a questionnaire sent to the patient by the trial center.


This study will provide evidence on the effectiveness of oxygen supplementation for the treatment of stroke and whether nocturnal oxygen is a potentially beneficial therapy regimen.

Trial registration

This trial is registered with the ISRCTN register ID number ISRCTN52416964

Stroke; Oxygen supplementation; Oxygen; Hypoxia; Oximetry; Oxygen saturation