Bronchodilator delivery by metered-dose inhaler in mechanically ventilatedCOPD patients: influence of flow pattern

In mechanically ventilated patients the flow pattern during bronchodilator delivery by metered-dose inhaler (MDI) could be a factor that might influen ce the effectiveness of this therapy, In order to test this the effect of t wo different inspiratory flow patterns on the bronchodilation induced by be ta(2)-agonists administered via MDI and spacer in a group of mechanically v entilated patients with chronic obstructive pulmonary disease (COPD) was ex amined, Eighteen mechanically ventilated patients with COPD, were prospectively ran domized to receive two (n=8, protocol A) or sis (n=10 protocol B) puffs sal butamol (100 mu g . puff(-1)) either under pressure control (decelerating f low pattern) or under volume control (square wave flow pattern), With both modes, tidal volume and inspiratory time were identical. Salbutamol was adm inistered via an MDI adapted to the inspiratory limb of the ventilator circ uit using an aerosol cloud-enhancer spacer. After a 6-h washout, patients w ere crossed over to receive the same dose of salbutamol (200 or 600 mu g, r espectively in protocols A and B) by the alternative mode of administration . Static and dynamic airway pressures, minimum (Rint) and maximum (Rrs) ins piratory resistance and the difference between Rrs and Rint (Delta R) were measured before and at 15, 30 and 60 min after salbutamol, Independent of the dose, salbutamol caused a significant decrease in dynami c and static airway pressures, Rint and Rrs, These changes were not influen ced by the inspiratory flow pattern and were evident at 15, 30 and 60 min a fter salbutamol, It is concluded that salbutamol delivered via metered dose inhaler and spacer device, induces significant bronchodilation in mechanic ally ventilated patients with chronic obstructive pulmonary disease, the ma gnitude of which is not affected by the inspiratory flow/time profile.