Randomised controlled crossover trial of the effect on PtCO2 of oxygen-driven versus air-driven nebulisers in severe chronic obstructive pulmonary disease
Emerg Med J 2012;29:894-898
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. While a large proportion of nebulisers used in the pre-hospital environment are oxygen driven, there have been questions on whether ambulances should have a compressed air supply, in addition to oxygen.
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 (PtCO2) and oxygen saturations were recorded at 5 min intervals during the study. The primary outcome was the PtCO2 after the completion of the second bronchodilator treatment.
PtCO2 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 PtCO2 of 11 mm Hg after the first bronchodilator nebulisation driven by oxygen. The mean PtCO2 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).
The authors found that nebulisers driven with oxygen result in significantly higher levels of PtCO2 than those driven with air in patients with severe COPD.