Albuterol delivery by metered-dose inhaler in a pediatric high-frequency oscillatory ventilation model

Objectives: To assess albuterol delivery by metered-dose inhaler (MDI) in a pediatric lung model ventilated by high-frequency oscillatory ventilation (HFOV). The percentage albuterol dose lost in the circuit's expiratory limb and the effects of operating frequency, inspiratory time, and use of a spacer were also determined. Design: Prospective in vitro laboratory study. Setting: Research laboratory. Interventions: A model consisting of a HFOV and circuit, 4.5-mm endotracheal tube, and lung simulator was assembled. Ventilator settings were the following: humidified FIO2 of 1.0; mean airway pressure of 28 cm H2O; operating frequency of 10 Hz; pressure amplitude of 55 cm H2O; bias gas flow to maintain mean airway pressure; 30% inspiratory time; and temperature of 35 degrees C (95 degrees F). Lung simulator compliance and resistance values were consistent with pediatric patients with pulmonary disease. A total of ten MDI canisters were used to administer 2000 mu g of albuterol with a spacer. Circuit filters placed proximal to the lung simulator and in the circuit's expiratory limb collected albuterol exiting the endotracheal tube and any albuterol lost, respectively. Filters were rinsed with water and albuterol concentrations determined by high performance liquid chromatography. Albuterol administration was repeated at operating frequencies of 5 and 15 Hz, inspiratory times of 40% and 50%, and with an actuator instead of a spacer. Each test condition was repeated ten times. Analysis of variance or Student's t-test was used to determine significant differences in albuterol delivered or lost among the operating frequencies and inspiratory times, and between the spacer and actuator. Measurements and Main Results: Albuterol delivery to the lung simulator was <1% of the administered dose regardless of the operating frequency, inspiratory time, or use of a spacer or actuator. Albuterol lost in the expiratory limb ranged from 3.28% to 14.89% of the administered dose. Conclusions: These in vitro results suggest albuterol delivery by MDI in a pediatric model of HFOV is negligible, regardless of the operating frequency, inspiratory time, or use of a spacer or actuator.