A Comparison of 2 Methods of Continuous Aerosol Administration During Methacholine Challenge Testing

BACKGROUND: Exposure to the bronchoconstricting agent methacholine is a potential hazard to technical staff during methacholine challenge testing, which remains a useful and frequently per-formed 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. METHODS: We tested 2 variations of the tidal-breathing method of measuring the methacholine provocational concentra-tion (PC20, 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 pre-cluded the release of methacholine-containing droplets into the environment. We performed du-plicate methacholine challenge tests with 10 subjects who had a wide range of PC20. The tests were done in random order, and each subject performed one test using the mask and one using the T-piece/filter system. RESULTS: With the mask system the geometric mean PC20 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. CONCLUSION: 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. Key words: metha-choline challenge test, technician exposure, T-piece, filter. [Respir Care 2006;51(1):46–48. © 2006 Daedalus Enterprises