Introduction: In 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.
Methods: We 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.
Results: 208 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).
Conclusion: Omitting 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.
Keywords: Asthma; Methacholine challenge testing; Respiratory physiology.