Bronchodilator delivery by metered-dose inhaler in mechanically ventilatedCOPD patients: influence of tidal volume

Objective: The delivery of bronchodilator drugs with metered-dose inhaler ( MDI) and a spacer in mechanically ventilated patients has become a widespre ad practice. However, the various ventilator settings that influence the ef ficacy of MDI are not well established. The tidal volume (V-T) during drug delivery has been suggested as one of the factors that might increase the e ffectiveness of this therapy. To test this, the effect of two different V-T on the bronchodilation induced by beta(2)-agonists administered with MDI a nd a spacer in a group of mechanically ventilated patients with chronic obs tructive pulmonary disease (COPD) was examined. Methods: Nine patients with COPD, mechanically ventilated on volume-control led mode, were prospectively randomised to receive six puffs of salbutamol (S, 100 mu g/puff) either with a V-T of 8 ml/kg (normal V-T 582 +/- 85) or with a V-T of 12 ml/kg thigh V, 912 +/- 137). With both modes inspiratory f low was identical. S was administered with an MDI adapted to the inspirator y limb of the ventilator circuit using an aerosol cloud enhancer spacer. Af ter a 6-h washout, patients were crossed-over to receive S by the alternati ve mode of administration. Static and dynamic airway pressures, minimum (Ri nt) and maximum (Rrs) inspiratory resistance, the difference between Rrs an d Rint (Delta R), static end-inspiratory respiratory system compliance (Cst ,rs), intrinsic positive end-expiratory pressure (PEEPi) and heart rate (HR ) were measured before and at 15, 30 and 60 min after S. Results: S caused a significant decrease in dynamic and static airway press ures, PEEPi, Rint and Rrs. These changes were not influenced by V-T and wer e evident at 15, 30 and 60 min after S. With normal and high V-T Cst,rs, De lta R and HR did not change after S. Conclusions: We conclude that S delivered with an MDI and a spacer device i nduces significant bronchodilation in mechanically ventilated patients with COPD, the magnitude of which is not affected by at least a 50% increase in V-T These results do not support the V-T manipulations when bronchodilator s are administered in adequate doses during controlled mechanical ventilati on.