Exhaled carbon monoxide in patients with lower respiratory tract infection.

The concentration of carbon monoxide (CO) in exhaled air is increased in patients with asthma, bronchiectasis and upper respiratory tract viral infections. However there is no information about the level of CO in patients with lower respiratory tract infection. We studied a group of 35 patients (22 males) aged 45 +/- 3 (SEM) years with cough productive of purulent phlegm and pyrexia in a general practice setting. All were non-smokers or ex-smokers and none had a previous history of respiratory problems or diabetes. We measured CO level in exhaled air before and after a course of antibiotics. Therapy was deemed successful when patient no longer complained of cough productive of purulent phlegm. Twenty-eight of 35 patients had elevated CO level at their initial visit. Twenty-two out of 35 patients reported clinical improvement after antibiotic treatment and this was associated with a fall in exhaled CO level from 5.2 +/- 0.5 ppm to 2.3 +/- 0.3 ppm (P < 0.0001). We suggest that simple CO measurements in exhaled air can detect the inflammatory process within the airways caused by infection and that a repeat measurement can be used to assess the nature of inflammation.