Introduction: The Stroke Oxygen Study (SO2S) primary analysis revealed that routine oxygen supplementation, either continuous or only at night, for 72h post stroke did not improve patient outcome. A previous study suggested that the benefits of oxygen therapy may vary with stoke severity.
Objectives: to establish whether routine oxygen supplementation early after acute stroke improves functional outcome for any predefined patient subgroups.
Methods: patients within 24h of hospital admission, with no definite indications or contraindications to oxygen treatment were eligible for inclusion to the SO2S. Participants were randomised 1:1:1 to continuous oxygen, oxygen at night (between 21:00-06:00) only, or to control (room air) for 72h. Oxygen was given at a rate of 3L/min if the baseline oxygen saturation was ≤93% and at 2L/min if it was >93%. Follow-up at 3 months was by postal questionnaire with telephone follow-up for non-responders.
Results: 8003 participants were recruited from 136 hospitals in the UK (April 2008 to June 2013); Median age was 74 (range 19-100) y, 4398 (54.9%) were male, and the baseline NIHSS score was 5 (range 0-34). None of the predefined subgroups of oxygen treatment before enrolment (p=0.16), oxygen saturation on air at randomization (p=0.94), baseline NIHSS p=0.60), final diagnosis (p=0.97), time since stroke onset (p=0.94), aetiology (p=0.86), age (p=0.94), SSV prognostic index (p=0.17), level of consciousness (p=1.00), history of heart failure (p=0.73) or of chronic obstructive airways disease (p=0.13) showed any statistically significant interactions. All odds ratios were close to one with a range of 0.79-1.29).
Conclusion: Routine oxygen therapy does not improve functional outcome at 90 days in any of the predefined subgroups including stroke type or severity.