Evaluation of Aerosol Generator Devices at 3 Locations in Humidified and Non-humidified Circuits During Adult Mechanical Ventilation

BACKGROUND: The position of the jet or ultrasonic nebulizer in the ventilator circuit impacts drug delivery during mechanical ventilation, but has not been extensively explored, and no study has examined all of the commonly used nebulizers.

METHODS: Drug delivery from jet, vibrating-mesh, and ultrasonic nebulizers and pressurized metered-dose inhaler (pMDI) with spacer was compared in a model of adult mechanical ventilation, with heated/humidified and non-humidified ventilator circuits. Albuterol sulfate was aerosolized at 3 circuit positions: (1) between the endotracheal tube and the Y-piece; (2) 15 cm from Y-piece; and (3) 15 cm from the ventilator, with each device (n = 3) using adult settings (tidal volume 500 mL, ramp flow pattern, 15 breaths/min, peak inspiratory flow 60 L/min, and PEEP 5 cm H₂O). The drug deposited on an absolute filter distal to an 8.0-mm inner-diameter endotracheal tube was eluted and analyzed via spectrophotometry (276 nm), and is reported as mean ± SD percent of total nominal or emitted dose.

RESULTS: The vibrating-mesh nebulizer, ultrasonic nebulizer, and pMDI with spacer were most efficient in position 2 with both non-humidified (30.2 ± 1.0%, 24.7 ± 4.4%, and 27.8 ± 3.3%, respectively) and heated/humidified circuits (16.8 ± 2.6%, 16.5 ± 4.3%, and 17 ± 1.0%, respectively). In contrast, the jet nebulizer was most efficient in position 3 under both non-humidified (14.7 ± 1.5%) and heated/humidified (6.0 ± 0.1%) conditions. In positions 2 and 3, all devices delivered approximately 2-fold more drug under non-humidified than under heated/humidified conditions (P < .01). At position 1 only the pMDI delivered substantially more drug than with the non-humidified circuit.

CONCLUSION: During mechanical ventilation the optimal drug delivery efficiency depends on the aerosol generator, the ventilator circuit, and the aerosol generator position.