A comparison of 2 methods of continuous aerosol administration during methacholine challenge testing

Exposure to the bronchoconstricting agent methacholine is a potential hazard to technical staff during methacholine challenge testing, which remains a useful and frequently performed test. There are several methods of performing the test. One of the 2 methods listed in the American Thoracic Society's guidelines is the 2-min tidal-breathing method. The methacholine can be inhaled using one of several methods. The loosely-fitting-mask method is likely to produce more contamination of the local environment than a filtered exhalation system.

We tested 2 variations of the tidal-breathing method of measuring the methacholine provocational concentration (PC(20), the dose that produces a 20% decrease in forced expiratory volume in the first second). One involved use of the open-mask technique and the other a T-piece-and-filter system that precluded the release of methacholine-containing droplets into the environment. We performed duplicate methacholine challenge tests with 10 subjects who had a wide range of PC(20). The tests were done in random order, and each subject performed one test using the mask and one using the T-piece/filter system.

With the mask system the geometric mean PC(20) was 4.7 mg/mL, versus 5.1 mg/mL with the T-piece-filter system (p = 0.36). These values are very close and would not be substantially different clinically.

The 2 methods are equivalent, and the low cost of the products used in the T-piece/filter method makes it suitable for reducing technician exposure to methacholine, using potentially completely disposable components.