Aerosol deposition in the respiratory tract under mechanical ventilation: impact of nebulizer technology and ventilation mode

Aerosol therapy in mechanically ventilated patients is common in intensive care units but lacks standardized practices and clinical evidence. Aerosol deposition depends on nebulizer type, ventilation mode, circuit position, and patient characteristics. This study examined how ventilation mode and nebulization technology affect regional aerosol deposition using a validated ex vivo porcine model. Four experimental conditions compared two nebulization technologies - vibrating mesh nebulizer (VMN) and jet nebulizer (JN) - during two ventilation modes: spontaneous ventilation with pressure support and volume-controlled ventilation. Radiolabeled tracer ( 99m Tc-DTPA) quantified regional aerosol deposition throughout the ventilator circuit and respiratory tract via scintigraphic imaging. Each experiment was repeated three times using different porcine airways ventilated in a hypobaric chamber. Particle size analysis determined Mean Mass Aerosol Diameter (MMAD) and Geometric Standard Deviation. VMN produced significantly higher nebulized fractions (97-98%) versus JN (30-32%). Pulmonary deposition was consistently higher with VMN: 47% versus 9% for JN during spontaneous ventilation, and 57% versus 13% during volume-controlled ventilation. Nebulization technology affected deposition more than ventilation mode. Central-to-total lung deposition ratio was higher for VMN in volume-controlled mode. VMN produced larger particles (MMAD 4.6 μm) than JN (MMAD 3.7 μm) with similar dispersion profiles. This regional deposition comparison study demonstrates VMN significantly increased lung deposition up to fivefold, primarily through lower residual doses and higher aerosol output. No significant difference existed between ventilation modes, though volume-controlled ventilation trended higher. Results strongly support using VMN over JN in intensive care units as the key factor for optimizing aerosol delivery.