Inhaled beta agonists and acute asthma

Salbutamol treatment of acute severe asthma in the ED: MDI versus hand-held nebulizer

The objectives of this study were to compare the efficacy of salbutamol delivered by either metered-dose inhaler plus spacer (MDI-spacer) or by wet nebulization (NEB), and to determine the relationships between physiologic responses and plasma salbutamol concentrations. Asthmatic patients presenting to the emergency department (ED) with acute severe asthma (forced expiratory volume in the first second [FEV1] less than 50% of predicted) were enrolled in a randomized, double-blind, parallel-group study. The MDI-spacer group received salbutamol, delivered via MDI into a spacer device, in four puffs actuated in rapid succession at 10-minute intervals (2.4 mg/h). The NEB group was treated with nebulized salbutamol, 1.5 mg, via nebulizer at 15-minute intervals (6 mg/h). Doses were calculated on the basis of the percentage of total dose that reaches the lower airway with both methods. The protocol involved 3 hours of this treatment. Mean peak expiratory flow rate (PEFR) and FEV1 improved significantly over baseline values for both groups (P=.01). However, there were no significant differences between both groups for PEFR and FEV1 at any point studied. The examination of the relationships between cumulative dose of salbutamol and change in FEV1 showed a significant linear relationship (P=.01) for both methods (MDI r=.97; NEB r=.97). The regression equations showed that for every 1 mg of salbutamol by MDI-spacer, 2.5 mg are needed from nebulization to have equal therapeutic response. At the end of treatment, the salbutamol plasma levels were 10.1+/-1.6 ng/ml for the MDI-spacer group and 14.4+/-2.3 ng/ml for the NEB group (P=.0003). Both groups showed a nonsignificant heart rate decrease. A significant group-by-time interaction means that differences between groups increased with time (P=.04). Additionally, the NEB group presented a higher incidence of tremor (P=.03) and anxiety (P=.04), reflecting larger systemic absorption of salbutamol. These data indicate that when doses used are calculated on the basis of the percentage of total drug that reaches the lower airway, there was equivalent bronchodilatation after salbutamol administered by either MDI-spacer or nebulization in patients with acute severe asthma. However, nebulizer therapy produced greater side effects related to the increase in salbutamol absorption and higher plasma level.

Therapeutic response patterns to high and cumulative doses of salbutamol in acute severe asthma

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 microg) at 10-min intervals. The protocol involved 3 h of this treatment (1,200 microg 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 < or =2.4 mg of the drug within 1 h to reach the discharge threshold, whereas the remainder 30% need > or =3.6 mg. In 30% of subjects, salbutamol was ineffective. These patients were characterized by a more severe disease as judged by previous beta2-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 PEFR 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.

Metered dose inhaler salbutamol treatment of asthma in the ED: comparison of two doses with plasma levels

Two cumulative doses of salbutamol delivered by metered dose inhaler (MDI) with a pear-shaped spacer were compared (400 micrograms vs 600 micrograms at 10-minute intervals). Twenty-two patients (mean age 35.1 +/- 11.1 years) with acute exacerbation of asthma were randomly selected, in a double-blind fashion, to receive salbutamol delivered with MDI into a spacer device in 4 puffs at 10- minute intervals (100 micrograms or 150 micrograms per actuation) during 3 hours (1200 micrograms or 1800 micrograms each 30 minutes). Mean peak expiratory flow rate (PEFR) and forced expiratory volume in the first second (FEV1) improved significantly over baseline values for both groups (P < .001). Nevertheless, there were no significant differences between both groups for PEFR and FEV1 at any time point studied. A significant net reduction of heart rate was observed in the 400 microgram group (P < .01). On the other hand, a significant increase in heart rate was observed in the 600 microgram group (P < .001). The QTc interval did not show a significant prolongation, and the two groups presented moderate decreases of serum potassium levels. There was a significant dose-related increase (P = .027) in Sao2. Additionally, the 600 microgram group generated a serum glucose level increase from 0.85 +/- 0.12 mg/100 mL to 1.04 +/- 0.25 mg/100 mL (P = .02), with a higher incidence in 4 symptoms (tremor, headache, palpitations, and anxiety). These data support the notion that the treatment of acute asthma patients in the emergency department setting with salbutamol, 2.4 mg/h, delivered by MDI and spacer (4 puffs at 10-minute intervals) produces satisfactory bronchodilation, low serum concentration, and minimal extrapulmonary effects. However, an increase of 50% of the dose (600 micrograms at 10-minute intervals) produced a nonsignificant, slightly better therapeutic response but with greater side effects, probably related to higher salbutamol levels.