Randomised controlled crossover trial of the effect on PtCO2 of oxygen-driven versus air-driven nebulisers in severe chronic obstructive pulmonary disease

Background The comparative safety of oxygen versus air-driven nebulised bronchodilators in patients with acute exacerbations of chronic obstructive pulmonary disease (COPD) is uncertain. A randomised controlled trial was performed to assess the effect on the arterial partial pressure of carbon dioxide of nebulised bronchodilator driven with oxygen versus air in stable severe COPD. Methods In an open label randomised study, 18 subjects with stable severe COPD attended on 2 days to receive nebulised bronchodilator therapy driven by air or oxygen. Subjects received 5 mg salbutamol and 0.5 mg ipratropium bromide by nebulisation over 15 min, then, after 5 min, 5 mg salbutamol nebulised over 15 min, followed by 15 min of observation. Transcutaneous carbon dioxide tension (Pt-CO2) and oxygen saturations were recorded at 5 min intervals during the study. The primary outcome was the Pt-CO2 after the completion of the second bronchodilator treatment. Results Pt-CO2 was higher with nebulised bronchodilator therapy delivered by oxygen, but decreased back to the level associated with air nebulisation 15 min after completion of the second nebulised dose. One subject experienced an increase in Pt-CO2 of 11 mm Hg after the first bronchodilator nebulisation driven by oxygen. The mean Pt-CO2 difference between the oxygen and air groups after the second nebulisation was 3.1 mm Hg (95% CI 1.6 to 4.5, p<0.001). Conclusion Nebulisers driven with oxygen result in significantly higher levels of Pt-CO2 than those driven with air in patients with severe COPD. Clinical trial registration number The study was registered on the Australian New Zealand Clinical Trials Registry (ACTRN12610000080022).