Effects of ventilator settings, nebulizer and exhalation port position on albuterol delivery during non-invasive ventilation: an in-vitro study.

BACKGROUND: Few studies have investigated the factors affecting aerosol delivery during non-invasive ventilation (NIV). Our aim was to investigate, using a bench-top model, the effect of different ventilator settings and positions of the exhalation port and nebulizer on the amount of albuterol delivered to a lung simulator.

METHODS: A lung model simulating spontaneous breathing was connected to a single-limb NIV ventilator, set in bi-level positive airway pressure (BIPAP) with inspiratory/expiratory pressures of 10/5, 15/10, 15/5, and 20/10 cmH2 O, or continuous positive airway pressure (CPAP) of 5 and 10 cmH2 O. Three delivery circuits were tested: a vented mask with the nebulizer directly connected to the mask, and an unvented mask with a leak port placed before and after the nebulizer. Albuterol was collected on a filter placed after the mask and then the delivered amount was measured with infrared spectrophotometry.

RESULTS: Albuterol delivery during NIV varied between 6.7 ± 0.4% to 37.0 ± 4.3% of the nominal dose. The amount delivered in CPAP and BIPAP modes was similar (22.1 ± 10.1 vs. 24.0 ± 10.0%, p = 0.070). CPAP level did not affect delivery (p = 0.056); in BIPAP with 15/5 cmH2 O pressure the delivery was higher compared to 10/5 cmH2 O (p = 0.033) and 20/10 cmH2 O (p = 0.014). Leak port position had a major effect on delivery in both CPAP and BIPAP, the best performances were obtained with the unvented mask, and the nebulizer placed between the leak port and the mask (p < 0.001).

CONCLUSIONS: In this model, albuterol delivery was marginally affected by ventilatory settings in NIV, while position of the leak port had a major effect. Nebulizers should be placed between an unvented mask and the leak port in order to maximize aerosol delivery.