Effect of a New Nebulizer Position on Aerosol Delivery during Mechanical Ventilation: A Bench Study

Abstract

BACKGROUND: The efficacy of placing nebulizers at the Y-piece vs at the manifold during mechanical ventilation (MV) has been reported, as have the effects of intermittent vs continuous nebulization. I studied the effects of a new nebulizer position, at the ventilator end of the circuit, by nebulizing food coloring at a target and using a colorimetry scale to quantitate aerosol delivery under various conditions. MATERIALS & METHODS: To create the visual colorimetry scale, I colored white bacteria filters yellow with nebulized food coloring, then exposed 30 of them for graded periods of time to nebulized blue food coloring, creating a colorimetry scale ranging from light yellow-green (Filter #1, exposed 5 s) to dark blue-green (Filter #30, exposed 150 s). Test Setup: A nebulizer was placed variously at the Y-piece, manifold, and ventilator positions in a P-B 7200 ventilator circuit. The distal end of the circuit was attached to an endotracheal tube that had a plain yellow target filter attached to its 'tracheal' end. Testing: Blue food coloring was nebulized during simulated MV, and the aerosol impacted on and colored the target filter. Continuous and intermittent nebulization and the different nebulizer positions were studied in seven combinations of position and mode. A 3-person jury then assigned, by consensus, a colorimetry-scale value to each target filter. The resulting number score for each test condition was then compared to scores for the other test conditions, yielding data showing which nebulizer conditions allowed more or less coloring (representing medication) to reach the 'trachea.' RESULTS: Continuous nebulization from the ventilator position delivered significantly more aerosol (p < 0.00001) than did any other nebuilzer position or mode. CONCLUSIONS: While the ventilator position of the nebulizer was the most effective, further studies are needed to determine whether changes in particle size through a long circuit result in more or less deposition of medication in large versus more peripheral airways. For this reason, in our institution we place the nebulizer at the manifold for routine administration of bronchodilators during MV.