Randomised controlled trial of high concentration versus titrated oxygen therapy in severe exacerbations of asthma

The effect on Paco2 of high concentration oxygen therapy when administered to patients with severe exacerbations of asthma is uncertain.

106 patients with severe exacerbations of asthma presenting to the Emergency Department were randomised to high concentration oxygen (8 l/min via medium concentration mask) or titrated oxygen (to achieve oxygen saturations between 93% and 95%) for 60 min. Patients with chronic obstructive pulmonary disease or disorders associated with hypercapnic respiratory failure were excluded. The transcutaneous partial pressure of carbon dioxide (Ptco2) was measured at 0, 20, 40 and 60 min. The primary outcome variable was the proportion of patients with a rise in Ptco2 ≥4 mm Hg at 60 min.

The proportion of patients with a rise in Ptco2 ≥4 mm Hg at 60 min was significantly higher in the high concentration oxygen group, 22/50 (44%) vs. 10/53 (19%), RR 2.3 (95% CI 1.2 to 4.4, p<0.006). The high concentration group had a higher proportion of patients with a rise in Ptco2 ≥8 mm Hg, 11/50 (22%) vs. 3/53 (6%), RR 3.9 (95% CI 1.2 to 13.1, p=0.016). All 10 patients with a final Ptco2 ≥45 mm Hg received high concentration oxygen therapy, and in five there was an increase in Ptco2 ≥10 mm Hg.

High concentration oxygen therapy causes a clinically significant increase in Ptco2 in patients presenting with severe exacerbations of asthma. A titrated oxygen regime is recommended in the treatment of severe asthma, in which oxygen is administered only to patients with hypoxaemia, in a dose that relieves hypoxaemia without causing hyperoxaemia. Clinical trial number ACTRN12607000131459.