Effect of inspiratory flow rate on beta(2)-agonist induced bronchodilationin mechanically ventilated COPD patients

Objectives: To test the effect of two different inspiratory flow rates on t he bronchodilation induced by beta (2)-agonists administered by metered dos e inhaler (MDI). Patients: Ten patients with acute exacerbation of chronic obstructive pulmo nary disease and receiving mechanical ventilation with constant inspiratory flow (V'(I)). Design: Patients received four puffs of salbutamol (100 mug/puff) with eith er low V'(I) (0.6 l/s) or high V'(I) (1.2 1/s) administered with an MDI ada pted to inspiratory limb of the ventilator circuit using an aerosol cloud e nhance spacer. After a 6-h washout patients were crossed-over to receive th e drug by the alternative mode of administration. Measurements and results: Static and dynamic airway pressures, intrinsic po sitive end-expiratory pressure, and minimum and maximum inspiratory resista nce values showed a significant decrease after salbutamol. These changes we re not affected by the inspiratory now rate and were evident 15, 30, and 60 min after administration. Heart rate, static end-inspiratory respiratory s ystem compliance, and the difference between minimum and maximum inspirator y resistance were unchanged after salbutamol. Conclusions: Salbutamol delivered by MDI and spacer device induces signific ant bronchodilation in mechanically ventilated patients with chronic obstru ctive pulmonary disease, but the magnitude of the effect is not affected by the inspiratory flow rate. These results do not support now rate manipulat ions when bronchodilators are administered during controlled mechanical ven tilation.