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The SO2S study, one of the largest ever studies of the treatment of stroke, has found no worthwhile benefit from giving patients oxygen during the first few days following stroke (JAMA, 26 September 2017).

x-ray showing location of a stroke in the brain.

Stroke is the second largest cause of death worldwide.  Every year 150,000 people in the UK suffer a stroke and almost one in six dies within the first month after a stroke. Half of those who survive are left with a disability and rely on other people to help them with their day-to-day activities, affecting the lives of their friends and families.

A lower than normal concentration of oxygen in the blood, mild hypoxia, is common in stroke patients, and may lead to further damage to a brain that is already short of oxygen because, during and after a stroke, blood supply to part of the brain is reduced. Oxygen treatment is widely used after stroke. It is cheap, easy to give, and available in all hospitals, however, it could have adverse effects: oxygen levels that are too high could damage brain cells, there is an increased risk of infection and the tubing used to give the oxygen restricts movement, which is believed to help recovery. Previous research studies of giving oxygen after stroke have been small with some showing benefit and others harm, so it is uncertain whether the benefits of oxygen treatment outweigh the risks.

The SO2S study of oxygen after stroke is one of the largest ever studies of the treatment of stroke and was published in JAMA today. Just over 8,000 patients admitted with a stroke to 136 hospitals in the UK between April 2008 and June 2013 took part. The study aimed to determine whether or not it is worthwhile to give patients oxygen during the first few days following stroke. It also compared oxygen given overnight only with oxygen given continuously.

Patients who had no definite need for oxygen were randomly allocated to one of 3 treatments: continuous oxygen via nasal tubing for 72 hours, oxygen overnight for three consecutive nights, or no routine oxygen unless a definite need for oxygen arose. Patients were assessed after one week by a research nurse and after 90 days by postal questionnaire or telephone interview. 

The results showed that oxygen supplementation did not improve functional outcome at 90 days when compared with the control group. There was also no difference between the groups given oxygen continuously or at night only.  Even patients who were considered most likely to benefit such as those presenting early, those with lower baseline oxygen levels, or with more severe stroke, and patients with pre-existing heart and lung problems did not have any better outcome with oxygen.

Patients with very low oxygen levels were excluded but, for other patients admitted to hospital with a stroke, the SO2S study provides clear and unambiguous evidence that they do not need routine prophylactic oxygen treatment. Giving oxygen to stroke patients does not improve recovery from stroke.

Professor Christine Roffe, who led the study, said “Patients with very low oxygen levels still need oxygen treatment, so it remains important to monitor oxygen levels, but there is no need to give oxygen routinely to stroke patients.” 

Professor Richard Gray, senior author of the study, from the MRC Population Health Research Unit,  commented “Because the Stroke Oxygen Study was so big, even a very small benefit from oxygen would have been detected. We can be really confident in these results.