Routine use of low-dose oxygen supplementation in the first days after stroke doesn’t improve overall survival or reduce disability, according to a large new study.
The poststroke death and disability odds ratio was 0.97 for those receiving one of two continuous low-dose oxygen protocols, compared with the control group (95% confidence interval, 0.89-1.05; P = .47).
The Stroke Oxygen Study (SO2S) was a single-blinded, randomized, controlled trial that recruited 8,003 adults with a diagnosis of acute stroke within 24 hours of hospital admission, drawing from 136 centers in the United Kingdom, according to an article in JAMA (2017;318:1125-35). A total of 7,677 participants (96%) had data available for analysis of the primary outcome measure, a composite of death and disability 90 days post stroke.
Participants, who were not hypoxic at enrollment, were randomized 1:1:1 to receive continuous oxygen supplementation for the first 72 hours after stroke, to receive supplementation only at night, or to receive oxygen when indicated by usual care protocols. The average participant age was 72 years and 55% were men in all study arms, and all stroke severity levels were included in the study.
Patients in the two intervention arms received 2 L of oxygen by nasal cannula when their baseline oxygen saturation was greater than 93%, and 3 L when oxygen saturation at baseline was 93% or less. Participation in the study did not preclude more intensive respiratory support when clinically indicated.
Nocturnal supplementation was included as a study arm for two reasons: Poststroke hypoxia is more common at night, and night-only supplementation would avoid any interference with early rehabilitation caused by cumbersome oxygen apparatus and tubing.
Not only was no benefit seen for patients in the pooled intervention arm cohorts, but no benefit was seen for night-time versus continuous oxygen as well. The odds ratio for a better outcome was 1.03 when comparing those receiving continuous oxygen to those who only received nocturnal supplementation (95% CI, 0.93-1.13; P = .61).
First author Christine Roffe, MD, and her collaborators in the Stroke Oxygen Study Collaborative Group also performed subgroup analyses and did not see benefit of oxygen supplementation for older or younger patients, or for patients with chronic obstructive pulmonary disease, heart failure, or more severe strokes.
“Supplemental oxygen could improve outcomes by preventing hypoxia and secondary brain damage but could also have adverse effects,” according to Dr. Roffe, consultant at Keele (England) University and her collaborators.
A much smaller SOS pilot study, they said, had shown improved early neurologic recovery for patients who received supplemental oxygen after stroke, but the pilot also “suggested that oxygen might adversely affect outcome in patients with mild strokes, possibly through formation of toxic free radicals,” wrote the investigators.
These were effects not seen in the larger SO2S study, which was designed to have statistical power to detect even small differences and to do detailed subgroup analysis. For patients like those included in the study, “These findings do not support low-dose oxygen in this setting,” wrote Dr. Roffe and her collaborators.
Dr. Roffe reported receiving compensation from Air Liquide. The study was funded by the United Kingdom’s National Institute for Health Research.
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