Effect of inspiratory flow rate on beta2-agonist induced bronchodilation in mechanically ventilated COPD patients

To test the effect of two different inspiratory flow rates on the bronchodilation induced by beta2-agonists administered by metered dose inhaler (MDI).

Ten patients with acute exacerbation of chronic obstructive pulmonary disease and receiving mechanical ventilation with constant inspiratory flow (V'I).

Patients received four puffs of salbutamol (100 microg/puff) with either low V'I (0.6 l/s) or high V'I (1.2 l/s) administered with an MDI adapted to inspiratory limb of the ventilator circuit using an aerosol cloud enhance spacer. After a 6-h washout patients were crossed-over to receive the drug by the alternative mode of administration.

Static and dynamic airway pressures, intrinsic positive end-expiratory pressure, and minimum and maximum inspiratory resistance values showed a significant decrease after salbutamol. These changes were not affected by the inspiratory flow rate and were evident 15, 30, and 60 min after administration. Heart rate, static end-inspiratory respiratory system compliance, and the difference between minimum and maximum inspiratory resistance were unchanged after salbutamol.

Salbutamol delivered by MDI and spacer device induces significant bronchodilation in mechanically ventilated patients with chronic obstructive pulmonary disease, but the magnitude of the effect is not affected by the inspiratory flow rate. These results do not support flow rate manipulations when bronchodilators are administered during controlled mechanical ventilation.