Effect of Nebulizer Location and Spontaneous Breathing on Aerosol Delivery During Airway Pressure Release Ventilation in Bench Testing.

BACKGROUND

Airway pressure release ventilation (APRV) maintains a sustained airway pressure over a large proportion of the respiratory cycle, and has a long inspiratory time at high pressure. The purpose of this study was to determine the influence of the APRV with and without spontaneous breathing on albuterol aerosol delivery with a continuous vibrating-mesh nebulizer (VMN) placed at different positions on an adult lung model of invasive mechanical ventilation.

METHODS

An adult lung model was assembled by connecting a ventilator with a dual-limb circuit to an 8-mm inner diameter endotracheal tube (ETT) and collecting filter attached to a test lung with set compliance of 0.1 L/cmHO and resistance of 0.5 cmHO/(L·s). Four ventilator modes were compared: pressure control ventilation (PCV) with no bias flow, PCV with bias flow of 6 L/min (PCV), APRV with no spontaneous breaths (APRV), and APRV with spontaneous breath trigger (APRVs). Peak inspiratory pressure, peak end-expiratory pressure, aerosol dose, and nebulization time were similar for all modes. The VMN was placed (1) between Y-piece and inspiratory limb, (2) at the gas outlet of a heated humidifier, and (3) at the gas inlet of a heated humidifier. Albuterol sulfate (5 mg/2.5 mL) was administered with each run and collected on a filter distal to the ETT. Deposited drug was eluted from each filter (purified water) and analyzed by UV spectrophotometry at 276 nm. Analysis of variance [general linear model (GLM) multivariate] was performed using the linear model of multiple variables, significance at p < 0.05.

RESULTS

Albuterol (in micrograms, mean ± standard deviation) delivered was higher with VMN placed at the gas inlet of the humidifier with each mode of ventilation (p < 0.01). APRVs has the highest albuterol delivery followed by PCV, PCV, and APRV (1706.2 ± 60.9 μg vs. 1490.6 ± 61.1 μg vs. 1182.3 ± 61.4 μg vs. 1153.1 ± 99.7 μg, respectively, p < 0.001). The minute volume was positively correlated with the inhaled albuterol dose.

CONCLUSIONS

Spontaneous breathing increased the albuterol delivery during APRV, compared with APRV alone and PCV modes. Placing the nebulizer proximal to the ventilator was more efficient for all modes tested.