Background: Early studies have found better clinical efficiency when a nebulizer was used with noninvasive positive pressure ventilation (NPPV), compared with spontaneous breathing without NPPV. However, very limited research addressed factors that might affect aerosol delivery. This study aimed to investigate the influence of exhalation valves and nebulizer positions on aerosol delivery during NPPV.
Methods: We determined the efficiency of aerosol delivery in patients receiving NPPV with a lung model that simulates spontaneous breathing. Single-arch exhalation port, plateau exhalation valve, and whisper swivel were chosen as exhalation valves under different levels of inspiratory and expiratory pressures. A nebulizer was filled with 1 mL of 0.5% albuterol solution in 3 mL of normal saline, driven with 8 L/min oxygen, and placed at either a proximal position in the ventilator circuit (near the ventilator outlet, where humidifiers are usually connected) or a distal position in the ventilator circuit (between exhalation valve and lung model connection). Albuterol was collected by filters and then measured by ultraviolet spectrophotometry. The velocities of gas flow were also measured at different nebulizer positions.
Results: Significant differences in the gas flow velocity were shown between proximal and distal positions of the breathing circuit under four combinations of inspiratory and expiratory pressure levels (15/5, 15/10, 25/5, and 25/10 cmH2O) (p<0.05). When the nebulizer was positioned distally, the single-arch exhalation port had the highest aerosol delivery, and the whisper swivel had the lowest aerosol delivery (p<0.05). When the nebulizer was placed proximally, the single-arch exhalation port had lower efficiency of aerosol delivery than the whisper swivel and plateau exhalation valve (p<0.05). In addition, higher inspiratory pressure was associated with increased aerosol delivery (p<0.05). The influence of expiratory pressure on aerosol delivery appeared too complex to predict.
Conclusions: The type of exhalation valve and the position of the nebulizer in the ventilator circuit have a significant influence on the efficiency of aerosol delivery during NPPV. As a result, with different exhalation valves, an appropriate nebulizer position should be carefully chosen, and the inhaled dose should be adjusted after accurate prediction of aerosol delivery to ensure optimal clinical efficacy.