A pilot study measuring mixed venous carbon dioxide levels in students with and without a diagnosis of asthma

Objectives To pilot a protocol for measuring mixed venous carbon dioxide levels in individuals with asthma and establish likely values and variance for future power calculations.

Design Preliminary pilot study comparing two groups of individuals defined as asthmatic and non-asthmatic.

Setting Lung function laboratory in a regional teaching hospital.

Participants Eleven university students, five with a diagnosis of asthma and six with no known disorders.

Measurements Mixed venous carbon dioxide levels; spirometry.

Results Mixed venous carbon dioxide levels in the students with asthma ranged from 5.08 to 5.71kPa (mean 5.35kPa), and in the healthy students they ranged from 5.62 to 6.45kPa (mean 6.01kPa). The mean difference in mixed venous carbon dioxide levels between the two groups was 0.66kPa (95% confidence interval 0.28–1.03).

Conclusion This pilot study has demonstrated that a protocol using non-invasive mixed venous carbon dioxide measures is acceptable to people with asthma. It has also added to the evidence suggesting that asthmatic individuals have lower levels of carbon dioxide than the healthy population, even when they are stable and asymptomatic.