Influence of respiratory efforts on b2-agonist induced bronchodilation in mechanically ventilated COPD patients: A prospective clinical study

SummaryBackgroundSeveral in vitro studies have shown that at similar tidal volume (VT), bronchodilator delivery to target sites is significantly lower during controlled mechanical ventilation (CMV) than that during simulated spontaneous breathing. However, the influence of active respiratory efforts on the magnitude of b2-agonist induced bronchodilation in mechanically ventilated patients has not been examined.ObjectiveTo examine the influence of controlled and assisted modes of ventilatory support on the bronchodilative effect induced by b2-agonists administered with a metered dose inhaler (MDI) and a spacer device in a homogeneous group of mechanically ventilated patients with acute exacerbation of chronic obstructive pulmonary disease (COPD).MethodsProspective clinical study. Ten mechanically ventilated patients with acute exacerbation of COPD were prospectively randomized to receive 4 puffs of salbutamol (S, 100 μg/puff) either with volume-controlled (VC) or pressure-support (PS) ventilation. On PS the pressure level was such that VT was comparable between ventilatory modes. After a 6-h washout period, patients were crossed-over to receive the drug by the alternative mode of ventilation. Static and dynamic airway pressures, minimum (Rint) and maximum (Rrs) inspiratory resistance, the difference between Rrs and Rint (ΔR), end-inspiratory static compliance of the respiratory system (Crs), intrinsic positive end-expiratory pressure (PEEPi) and heart rate (HR) were measured before and at 15, 30, 60, 120, 180 and 240 min after S administration.ResultsS caused a significant decrease in dynamic and static airway pressures, PEEPi, Rint and Rrs. These changes were not influenced by the ventilatory mode and were evident at 15, 30, 60 and 120 min after S. HR, Crs and ΔR did not change after S administration.ConclusionsConsidering the use of propofol with its presumed bronchodilative properties as a shortcoming of our study, it is concluded that the magnitude of bronchodilation induced by salbutamol delivered by an MDI and a spacer device in mechanically ventilated COPD patients is not affected by the presence or absence of active respiratory efforts.