SO2S: No Benefit of Routine Oxygen in Acute Stroke

May 09, 2014

NICE, France — The biggest and most definitive study ever performed of routine oxygen supplementation in stroke has shown no benefit from such intervention.

The Stroke Oxygen Supplementation (SO2S) Study was presented here at the XXIII European Stroke Conference (ESC).

Lead investigator, Professor Christine Roffe, Keele University, United Kingdom, concluded: "Routine low-dose oxygen supplementation in unselected stroke patients does not improve outcome."

"Our message for clinical practice is that there is no point in giving oxygen to stroke patients just on the off chance that they might be hypoxic," she commented to Medscape Medical News. "Rather, it is better to find out if they are hypoxic and treat if they are."

Practice Varies Widely

She explained that current practice varies widely with different approaches in different countries and in different regions within countries.

"A lot of ambulance services give oxygen routinely, but guidelines have changed over the course of this study," Professor Roffe said. "When we started the trial all patients were given oxygen routinely and it was difficult to recruit into the study."

Since the guidelines changed in 2008-2009, there is now less use of oxygen in ambulances, she noted.

"We now advocate that ambulance staff measure oxygen saturation levels and only give oxygen if this is low," she added. "Oxygen saturation should also be measured in hospital, especially at night when it tends to fall."

8000 Patients

The SO2S trial was conducted to determine whether routine low-dose oxygen supplementation for 72 hours in patients with acute stroke improves outcome and, further, to establish whether nocturnal oxygen supplementation is more effective than continuous oxygen supplementation.

The trial randomly assigned 8000 patients with acute stroke in the United Kingdom within 24 hours of hospital admission to 3 groups: (1) continuous oxygen for 72 hours, (2) oxygen just given at night, or (3) no routine oxygen. Oxygen saturation was measured at least every 6 hours during the treatment period.

In the 2 treatment groups, oxygen was given by nasal cannula at a rate of 3 L/min if baseline oxygen saturation was below 93% or at 2 L/min if baseline oxygen saturation was above 93%.

Professor Roffe noted that wide inclusion criteria allowed for a representative sample of patients to be recruited.

Results showed that treatment with oxygen improved oxygen saturation levels.

Table. SO2S: Oxygen Saturation Levels

Endpoint Continuous Oxygen Nocturnal Oxygen Control P Value Oxygen vs Control P Value Continuous vs Nocturnal
Highest oxygen saturation (%) 99.1 98.8 98.3 <.0001 <.0001
Lowest oxygen saturation (%) 95.0 94.5 94.1 <.0001 <.0001


However, the primary outcome was disability at 90 days on the modified Rankin scale. This showed a neutral result with an odds ratio for a better outcome with oxygen vs control of 1.04 (95% confidence interval [CI], 0.95 - 1.13).

The comparison of continuous vs nocturnal oxygen was also neutral, with an odds ratio for a better outcome with continuous oxygen vs nocturnal of 0.97 (95% CI, 0.88 - 1.07).

There was also no difference in survival.

Further analyses will be performed to determine whether there are subgroups of patients who are likely to benefit.

Graeme Hankey, MBBS, MD, from the University of Western Australia, Crawley, Australia, cochairman of the session at which the trial was presented, praised the investigators for conducting the study.

"To randomize 8,000 patients is invaluable, and even if the result is neutral, it is an important finding," he commented to Medscape Medical News.

The study was funded by the NIHR Health Technology Assessment Programme.

XXIII European Stroke Conference (ESC). Presented May 7, 2014.


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