The delivery of bronchodilators with metered-dose inhaler (MDI) and a spacer in mechanically ventilated patients has become a widespread practice. However, the duration of action of bronchodilators delivered with this technique is not well established. The purpose of the study was to examine the duration of bronchodilation induced by short-term beta 2-agonists administered with an MDI and a spacer in a group of mechanically ventilated patients with exacerbation of chronic obstructive pulmonary disease (COPD). Ten patients with COPD, mechanically ventilated on volume-controlled mode, received 6 puffs of salbutamol (S, 100 micrograms/puff). S was administered with an MDI adapted to the inspiratory limb of the ventilator circuit using an aerosol cloud enhance spacer. Static and dynamic airway pressures, minimum (Rint) and maximum (Rrs) inspiratory resistance, the difference between Rrs and Rint (delta R), static end-inspiratory system compliance (Cst, rs), intrinsic positive end-expiratory pressure (PEEPi) and heart rate (HR) were measured before and at 15, 30, 60, 120, 180, 240, 300, 360 min after S. S caused a significant decrease in dynamic and static airway pressures, PEEPi, Rint and Rrs. These changes were evident at 15 minutes and remained significant for 2 hours after S. The duration of bronchodilation was highly variable and unpredictable among patients, lasting in some patients more than 4 hours while in others wearing off in less than 2 hours. We conclude that 6 puffs of S delivered with an MDI and a spacer device induces significant bronchodilation in mechanically ventilated patients with COPD, the duration of which is highly variable precluding guidelines regarding the time scheduled for dosing.