Evaluation of Bronchodilator Responsiveness in Mechanically Ventilated Patients

Airway pressure, flow, and volume were measured before and after administration of aerosolized metaproterenol during controlled mechanical inflation and stepwise deflation of the relaxed respiratory system in 13 mechanically ventilated patients. An increase in passive expiratory flow at constant respiratory system recoil pressure was considered evidence of bronchodilatation. In 10 patients, at a respiratory system recoil pressure of 6 cm H2O (P6), expiratory flow increased 21 to 500% above prebronchodilator level. in these 10 dynamically hyperinflated patients, an increase In (P6 was associated with a decrease in peak inspiratory pressure (Ppeak) (mean Δ = −4.7 cm H2O) and a decrease in intrinsic positive end-expiratory pressure (Peepi) (mean Δ = Δ2.4 cm H2O). The elastance of the respiratory system was not affected by metaproterenol, and the ΔPeePi corresponded to a mean decrease in end-expiratory lung volume of 0.20 L. The results are consistent with predictions based on a single-compartment model. When...