Bronchoprovocation with methacholine in children under two years old: a follow-up study.
Fifty-one wheezing babies (WB) under two years of age and 20 controls (C) within the same age range were submitted to a bronchial provocation test (BPT) with methacholine. The appearance of wheezing on pulmonary auscultation was used to determine PCW (provocative concentration of methacholine causing wheezing). For all tests, methacholine diluted in saline at increasing concentrations (0.025, 0.125, 0.25, 0.5, 1.0, 2.5, 5.0 and 10.0 mg/ml) was delivered with O2 (5 ml/min) via a face mask. Solution was inhaled through the mouth and nose during two minutes of quiet tidal breathing via a nebulizer containing a 2 ml volume. No collateral effects were observed, except for tachypnea and tachycardia. There was a statistically significant difference between the PCW for WB (2.3 mg/ml) and the PCW for C (9.2 mg/ml). A 5 mg/ml concentration of methacholine provides the clearest distinction between the WB and C groups. Indeed, we observed that 96% of WB and 25% of C demonstrated PCW below this concentration. In the WB group, those with mild symptoms had higher PCW values. When the BPT was repeated in 27 WB at an 8-month interval, statistically significant differences between the two PCV values were observed. The highest PCW values were evidenced in the second BPT. The use of BPT with methacholine could establish PCW as a parameter of bronchial hyperreactivity in infants.