Peak inspiratory flow through Turbuhaler in acute asthma

Efficient use of dry powder inhalers, such as Turbuhaler, is dependent on the generation of adequate inspiratory flow. It is not clear whether patients with acute asthma are able to generate adequate flow. Peak inspiratory flow (PIF) was measured through an empty Turbuhaler, and without this device, in 99 adults presenting to hospital with acute exacerbations of asthma. Where possible, patients were studied prior to nebulized bronchodilator therapy. Mean (SD) forced expiratory volume in one second (FEV1) was 1.2 (0.7) L, forced vital capacity (FVC) 2.1(1.0) L and peak expiratory flow (PEF) 199 (92) L.min-1. PIF without Turbuhaler was 152 (77) L.min-1 and correlated with PEF (r = 0.69). PIF through Turbuhaler was 60 (20) L.min-1 and weakly correlated with PEF (r = 0.35), and with PIF without Turbuhaler (r = 0.43). Two patients failed to generate the minimum inspiratory flow (30 L.min) required for efficient use of Turbuhaler; both recorded 26 L.min-1. Acute asthma is associated with considerable inspiratory, as well as expiratory airflow limitation. The relationship between inspiratory and expiratory airflow is not strong enough to predict whether patients with severe acute asthma will have difficulty using dry powder inhalers efficiently. Despite this, 98% of patients in this study generated inspiratory flow through Turbuhaler which would allow a therapeutically active amount of bronchodilator drug to be delivered to the airways.