Evaluation of Bronchial Hyperresponsiveness by Monitoring of Transcutaneous Oxygen Tension and Arterial Oxygen Saturation during Methacholine Challenge in Asthmatic Children

Abstract

Background. Bronchial hyperresponsiveness (BHR) is a key feature of asthma, but the measurement of BHR is hampered by the fact that most tests of airway caliber are difficult to conduct at a young age. Methacholine-induced bronchoconstriction is associated with significant hypoxemia, which can be assessed noninvasively by transcutaneous oxygen pressure (tcPO₂) and pulse oximetry. Evaluating BHR by monitoring tcPO₂ instead of respiratory resistance (Rrs) has been used over a wide age range in childhood.

Objective. To investigate whether there is a consistent relationship between changes in arterial oxygen saturation (SaO₂) and respiratory resistance (Rrs) similar to the relationship between tcPO₂ and Rrs during methacholine challenge in young children and to assess the usefulness of SaO₂ as a parameter for the indirect measurement of BHR.

Method. We performed methacholine inhalation challenge by monitoring SaO₂, tcPO₂ and Rrs in 37 asthmatic children 5 to 7 years of age. Consecutive doses of methacholine were doubled until a 10% decrease in tcPO₂ from the baseline was reached. We recorded the cumulative dose of methacholine (Dmin) at the inflection point of tcPO₂ (Dmin-tcPO₂), SaO₂ (Dmin-SaO₂), and Rrs(Dmin-Rrs).

Results. The mean value of Dmin-Rrs was 4.27 ± 2.02 units, the mean value of Dmin-tcPO₂ was 4.48 ± 2.01 units, and the mean value of Dmin-SaO₂ was 4.57 ± 0.20 units. Inhalation of increasing doses of methacholine raised Rrs curvilinearly and depressed tcPO₂ and SaO₂. There were no significant differences between any of the parameters. There were significant relationships between Dmin-tcPO₂ and Dmin-Rrs (r = 0.914, p < 0.001) and between Dmin-SaO₂ and Dmin-Rrs (r = 0.905, p < 0.001) and a relationship between Dmin-tcPO₂ and Dmin-SaO₂ (r = 0.949, p < 0.001).

Conclusion. We concluded that measurement of SaO₂ and/or tcPO₂ during methacholine inhalation challenge may be used to assess bronchial hyperresponsiveness. This study showed that both SaO₂ and tcPO₂ monitoring are safe, useful, and tolerable for use in children who are too young to cooperate with lung function tests.

Keywords:

• bronchial responsiveness
• childhood asthma
• oscillation technique
• oxygen saturation
• transcutaneous oxygen pressure