Albuterol delivery by 4 different nebulizers placed in 4 different positions in a pediatric ventilator in vitro model.

BACKGROUND: The type of aerosol generator and the position in the ventilator circuit are crucial to determine aerosol delivery during mechanical ventilation. We compared lung deposition of albuterol aerosols generated by 4 different nebulizers placed in-line in 4 different positions in a pediatric ventilator model.

METHODS: Two brands of continuously operated jet nebulizer (6 L/ min, oxygen), an ultrasonic, and a vibrating mesh were compared when placed at the ventilator, the humidifier, the Y-piece, and 30 cm before the Y-piece. The jet, ultrasonic, and vibrating mesh nebulizers were operated for 5, 15, and 15 min, respectively. The tested solutions contained 2.5 mg, 5.0 mg, and 7.5 mg of albuterol sulfate. The ventilator settings were: pressure-regulated volume control mode, tidal volume 200 mL, breathing frequency 20 breaths/min, PEEP 5 cm H2O, FIO2 0.4, inspiratory time 0.75 s, bias flow 2 L/min, and heater 37°C. The circuit was connected in series to a 5.5 mm cuffed endotracheal tube, a deposition filter, and a lung model. Albuterol was measured by spectrophotometry.

RESULTS: Intra-device comparison: the jet and vibrating mesh nebulizers performed best at either the ventilator or humidifier, and worst at the Y-piece. The ultrasonic nebulizer performed best at the humidifier and worst at the Y-piece. Inter-device comparison: the vibrating mesh nebulizer outperformed both jet nebulizers at all tested positions, and the ultrasonic nebulizer when placed at either the ventilator or the humidifier. Lung deposition increased for the jet and ultrasonic nebulizers, but not for vibrating mesh nebulizer, when increasing the loading volume while maintaining the nominal dose.

CONCLUSIONS: The vibrating mesh nebulizer was the most efficient device. The nebulizers were more efficient when placed at either the ventilator or the humidifier, and less efficient when placed at either the Y-piece or 30 cm from the Y-piece. These conclusions are valid for the tested conditions. Data regarding optimization of operating conditions should not be extrapolated among nebulizers of different operating principles.