title: Randomised controlled trial of high concentration versus titrated oxygen therapy in severe exacerbations of asthma.
abstract: BACKGROUND
  The effect on Paco2 of high concentration oxygen therapy when administered to patients with severe exacerbations of asthma is uncertain.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors: Medical Research Institute of New Zealand, Private Bag 7902, Wellington 6242, New Zealand.
authors: Kyle
authors: K
authors: Perrin
authors: Meme
authors: M
authors: Wijesinghe
authors: Bridget
authors: B
authors: Healy
authors: Kirsten
authors: K
authors: Wadsworth
authors: Richard
authors: R
authors: Bowditch
authors: Susan
authors: S
authors: Bibby
authors: Tanya
authors: T
authors: Baker
authors: Mark
authors: M
authors: Weatherall
authors: Richard
authors: R
authors: Beasley