Abstract
Objective To determine whether high concentration oxygen increases the PaCO2 in the treatment of community-acquired pneumonia.
Design Randomized 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 CO2 (PtCO2) was measured at 0, 20, 40 and 60 minutes.
Setting The Emergency Departments at Wellington, Hutt and Kenepuru Hospitals.
Participants 150 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 variables The primary outcome variable was the proportion of patients with a rise in PtCO2 >= 4 mmHg at 60 minutes. Secondary outcome variables included the proportion of patients with a rise in PtCO2 >= 8 mmHg at 60 minutes.
Results The proportion of patients with a rise in PtCO2 >= 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 PtCO2 >= 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 PtCO2 >= 4 mmHg, 20/35(57.1%) vs 5/39(12.8%), RR 4.5 (95% CI 1.9 to 10.6) P < 0.001.
Conclusions We conclude that high concentration oxygen therapy increases the PtCO2 in patients presenting with suspected community-acquired pneumonia. This suggests that the potential increase in PaCO2 with high concentration oxygen therapy is not limited to COPD, but may also occur in other respiratory disorders with abnormal gas exchange.