S145 HIGH CONCENTRATION OXYGEN CAUSES CARBON DIOXIDE RETENTION IN SEVERE ASTHMA: A RANDOMISED CONTROLLED TRIAL

¹K. Perrin, ¹M. Wijesinghe, ²M. Weatherall, ¹R. Beasley. ¹Medical Research Institute of New Zealand, Wellington, New Zealand, ²University of Otago, Wellington, Wellington, New Zealand

Introduction and Objectives The use of high concentration oxygen in acute exacerbations of chronic obstructive pulmonary disease (COPD) is well known to result in an increase in PaCO₂ in some patients. High concentration oxygen is often used routinely in acute severe asthma in the belief that it is safe and indicated in most patients; however, there is some evidence to suggest that this causes an increase in PaCO₂. In this randomised controlled trial we compared the effects of high flow vs titrated oxygen therapy on PaCO₂ levels in acute severe asthma.

Methods 80 patients with severe exacerbations of asthma (forced expiratory volume in 1 s (FEV₁) ⩽50% predicted) presenting to the Emergency Department of Wellington Hospital, New Zealand were recruited. Participants were randomised to receive either high flow oxygen (8 l/min via a medium concentration mask) or titrated oxygen (via nasal prongs or a medium concentration mask) adjusted to achieve oxygen saturations of 93–95% for 1 h along with routine asthma treatment. Transcutaneous carbon dioxide measurements (PtCO₂) were made at 0 and 60 min. The primary outcome variable was the proportion of patients with a rise in PtCO₂ ⩾4 mm Hg at 60 min. The secondary outcome variables were: the proportion of patients with a rise in PtCO₂ ⩾4 mm Hg and a PtCO₂ ⩾40 mm Hg at 60 min, the proportion of patients with a rise in PtCO₂ ⩾8 mm Hg and the mean rise in CO₂.

Results Three subjects withdrew from the high flow group leaving 36 for analysis in the high flow group and 41 in the titrated group. …