• Meme Wijesinghe, Kyle Perrin, Bridget Healy, Mark Weatherall, and Richard Beasley.
• Medical Research Institute of New Zealand, Wellington 6242, New Zealand.
• J R Soc Med. 2012 May 1;105(5):208-16.

ObjectiveTo determine whether high concentration oxygen increases the PaCO(2) in the treatment of community-acquired pneumonia.DesignRandomized controlled clinical trial in which patients received high concentration oxygen (8 L/min via medium concentration mask) or titrated oxygen (to achieve oxygen saturations between 93 and 95%) for 60 minutes. Transcutaneous CO(2) (PtCO(2)) was measured at 0, 20, 40 and 60 minutes.SettingThe Emergency Departments at Wellington, Hutt and Kenepuru Hospitals.Participants150 patients with suspected community-acquired pneumonia presenting to the Emergency Department. Patients with chronic obstructive pulmonary disease (COPD) or disorders associated with hypercapnic respiratory failure were excluded.Main Outcome VariablesThe primary outcome variable was the proportion of patients with a rise in PtCO(2) ≥4 mmHg at 60 minutes. Secondary outcome variables included the proportion of patients with a rise in PtCO(2) ≥8 mmHg at 60 minutes.ResultsThe proportion of patients with a rise in PtCO(2) ≥4 mmHg at 60 minutes was greater in the high concentration oxygen group, 36/72 (50.0%) vs 11/75 (14.7%), relative risk (RR) 3.4 (95% CI 1.9 to 6.2), P < 0.001. The high concentration group had a greater proportion of patients with a rise in PtCO(2) ≥8 mmHg, 11/72 (15.3%) vs 2/75 (2.7%), RR 5.7 (95% CI 1.3 to 25.0), P = 0.007. Amongst the 74 patients with radiological confirmation of pneumonia, the high concentration group had a greater proportion with a rise in PtCO(2) ≥4 mmHg, 20/35 (57.1%) vs 5/39 (12.8%), RR 4.5 (95% CI 1.9 to 10.6) P < 0.001.ConclusionsWe conclude that high concentration oxygen therapy increases the PtCO(2) in patients presenting with suspected community-acquired pneumonia. This suggests that the potential increase in PaCO(2) with high concentration oxygen therapy is not limited to COPD, but may also occur in other respiratory disorders with abnormal gas exchange.

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