Comparison with other studies
This is the first randomised controlled trial of oxygen
treatment for patients with a presumed acute exacerbation of chronic obstructive pulmonary disease in the
prehospital setting. We used mortality as the primary
outcome for the study because it is easily measured and
is less subject to confounding than are other health outcomes such as length of stay in hospital. Our death rate
of 9% in the high flow oxygen arm is similar to that seen
in audits of patients admitted to hospital with acute
exacerbations of chronic obstructive pulmonary
disease.28 29 Importantly, our study provides much
needed support for recent recommendations that
titrated oxygen, administered to achieve arterial oxygen saturations between 88% and 92%, should be used
in emergency situations.8 19
In the treatment per protocol analyses, patients with
chronic obstructive pulmonary disease who received
high flow oxygen were more likely to have respiratory
acidosis with a significantly higher arterial carbon
dioxide pressure. This is consistent with previous studies that have found that increased carbon dioxide and
respiratory acidosis are associated with poor outcomes, including increased mortality.15 16 30 Reversal
or prevention of these abnormalities by titrated oxygen
has been associated with better in-hospital
survival.19 31 32 Although patients given high flow oxygen were more acidotic, the arterial oxygen pressure
did not differ greatly between groups, which may
reflect the more rapid change that occurs in response to altering the fraction of inspired oxygen compared
with pH and carbon dioxide.