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

Abstract

BackgroundMild 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.MethodsParticipants 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.DiscussionThis 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 registrationThis trial is registered with the ISRCTN register ID number ISRCTN52416964

Hypoxia after stroke: a review of experimental and clinical evidence

“…At 6 months [83] there was no statistically significant difference between the two groups, although there remained a small trend towards overall benefit with supplemental oxygen. This data led to the Stroke Oxygen Study (SO 2 S) [84], in which 8003 patients within 24 h of hospital admission with acute stroke were randomized 1:1:1 to receive either continuous supplemental oxygen, supplemental oxygen only at night (9pm–7am) oxygen, or no supplemental oxygen treatment for 72 h. This study has completed recruitment and is expected to report in 2016.…”

Normobaric hyperoxygenation: a potential neuroprotective therapy for acute ischemic stroke?

“…These trials compared low-flow (2-3 L/min) oxygen supplementation to room air delivered from 24 to 72 h after ischemic or hemorrhagic stroke and provided inconclusive results [13,14]. The phase III Stroke Oxygen Study (N = 8000) with a similar objective [15] showed no benefit ofbut also no safety issues withlow-flow supplemental oxygen (results presented at the 23rd European Stroke Conference 2014 in Nice, France).…”

The effect of concentration and duration of normobaric oxygen in reducing caspase-3 and -9 expression in a rat-model of focal cerebral ischaemia

“…Certainly, a recent randomized controlled trial that investigated the effects of high flow (30-45 l per minute) NBO (100%) given to acute stroke patients for 8 h was terminated early due to excess mortality in the NBO group when compared to the group on air/low flow oxygen (40% versus 17%) (Singhal et al, 2014). However, preliminary findings from the largest NBO stroke trial to date, found no benefit with lower concentrations of NBO (24-32%) given up to 72 h in 8000 acute stroke patients (Roffe et al, 2014a(Roffe et al, , 2014b. Thus medium concentrations of 61% NBO may be safer and better tolerated by acute stroke patients than high NBO concentrations, but are possibly more effective than lower NBO concentrations at reducing short-term neurological impairment.…”