Study objectives: To examine the main therapeutic response patterns to high doses of salbutamol and to determine the factors that contribute to outcome in acute severe asthma.
Setting: The emergency department (ED) of a large, urban hospital with primary and referral care responsibilities.
Patients and design: One hundred sixteen consecutive patients with acute exacerbations of asthma were enrolled in the trial, using a prospective sequential design.
Interventions: All patients were treated with salbutamol delivered with a metered-dose inhaler into a spacer device in four puffs (400 µg) at 10-min intervals. The protocol involved 3 h of this treatment (1,200 µg, each 30 min).
Measures and results: A dose-response increase in pulmonary function was found, but only 70% improved sufficiently to be discharged. Of these, almost 70% required ≤2.4 mg of the drug within 1 h to reach the discharge threshold, whereas the remainder 30% need ≥3.6 mg. In 30% of subjects, salbutamol was ineffective. These patients were characterized by a more severe disease as judged by previous β2-agonist use, larger duration of attack before ED visit, and a more severe obstruction at presentation. However, the most important predictors of outcome were peak expiratory flow rate (PEFR) as percent of predicted, PEFR as liters per minute, and PEER variation over baseline value, all at 30 min.
Conclusions: This study described two different therapeutic response patterns to salbutamol. Almost 70% of patients were sensitive to salbutamol (good response pattern), and in this group, 2.4 to 3.6 mg represents optimal treatment. In the remainder 30% of patients (poor response pattern), salbutamol in high doses had little effect. However, the outcome was not determined by the intensity of the initial symptoms or by the value of the presenting PEFR, but rather by the early (30 min) short-term response to treatment.