Abstract
IntroductionIn methacholine challenge testing (MCT), skipping a methacholine dose is suggested if FEV1 falls by < 5%. Using a larger threshold may further shorten test duration, but data supporting this hypothesis is lacking. We evaluated the safety and consequences of using a 10% FEV1 fall as threshold to skip the next dose of methacholine in patients undergoing MCT.MethodsWe reviewed MCTs performed in our center in 2017–2018. A ≤ 10% FEV1 fall allowed the omission of the next methacholine dose. Patients of interest were those in which a dose was skipped after a previous FEV1 fall outside the usual range (5–10%, termed “skip5–10%”). Adverse events [AE; mild: > 1 nebulized salbutamol dose (2.5 mg) to reach basal FEV1, palpitations; severe: hypoxemia and/or need for medical attention or intervention] were compared in the skip5–10% group and others. Regression analysis was used to identify predictors of AE.Results208 MCTs were analysed (135 males, age 52 ± 15 years). Skip5–10% occurred 111 times in 90 tests. Prevalence of AE was 5% and all were mild. Patients who developed AEs had lower FEV1, FVC and FEV1/FVC ratio, and higher lung volume values (all p < 0.05), but similar prevalence of skip5–10% (36 vs. 44%, p = 0.64). Overall, MCTs in which at least one skip5–10% occurred had a lower mean number of doses (3.1 ± 0.6 vs. 3.5 ± 1.3 doses, p = 0.007). Baseline residual volume was independently related to the development of AEs (OR 1.05, 95% CI 1.01–1.10, p = 0.01), but not the presence of a skip5–10%, even when the skipped dose directly led to the reaching of PC20 (OR 5.40, 95% CI 0.73–39.22, p = 0.10).ConclusionOmitting a methacholine dose based on a ≤ 10% fall in FEV1 occurs frequently and has the potential to shorten test duration. AE are rare, but patients with worse baseline lung function and gas trapping are at increased risk of mild side effects.
Highlights
In methacholine challenge testing (MCT), skipping a methacholine dose is suggested if F EV1 falls by < 5%
We designed the following study to assess the safety and feasibility of using a 10% fall in FEV1 as a threshold to skip the dose of methacholine in patients undergoing MCT
Our main results can be summarized as follow: (1) the use of a 10% fall in F EV1 threshold to skip the methacholine dose allowed shortening the test in a large proportion of our subjects, (2) the use of this threshold was generally safe, with only mild adverse effects (AE) being reported and (3) resting lung function values, especially RV, were associated with the occurrence of AEs
Summary
In methacholine challenge testing (MCT), skipping a methacholine dose is suggested if F EV1 falls by < 5%. In order to further simplify and shorten MCTs, other methods have been described in more recent years, such as using threefold skips in methacholine concentration [6], the use of 2-tiered protocols [7] or the early stopping of the test when PC10, rather than PC20, was reached at a methacholine dose of ≤ 1 mg/ ml [8]. These changes made to the traditional MCT protocol offer the advantage of potentially decreasing test duration, while maintaining diagnostic precision and safety. We designed the following study to assess the safety and feasibility of using a 10% fall in FEV1 (as opposed to 5%) as a threshold to skip the dose of methacholine in patients undergoing MCT
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