Factors Influencing Aerosol Delivery During Invasive Ventilation

Background: Several factors influence aerosol delivery during mechanical ventilation, such as patient characteristics, device configuration, and ventilator settings. This study aimed to evaluate how ventilator settings, humidification, nebulizer positions, bias flows, and circuit adapters affected aerosol delivery during invasive ventilation. Methods: Using an in vitro model, aerosol delivery of albuterol (2.5 mg/3 mL) via a vibrating mesh nebulizer was tested under 28 conditions during invasive ventilation. A systematic stepwise ruling-out approach was taken over 3 phases: (1) dry circuit, (2) dry circuit with exhaled humidity, and (3) heated and humidified circuit with exhaled humidity. Variables included ventilator settings (high vs low), nebulizer positions (proximal to the endotracheal tube vs distal), bias flows (2 vs 5 L/min), and circuit adapters (Y- vs V-shaped). The variables deemed unimportant were progressively excluded in later phases. Each condition was tested 5 times. Drug deposition was collected on filters, eluted, and quantified using ultraviolet spectrophotometry at 276 nm. Results: High ventilator settings significantly increased inhaled doses compared with lower settings across most conditions (all P < .05), with the greatest absolute increase of inhaled dose was observed in dry circuits without exhaled humidity (11-22%). This effect was reduced to 4-7% with the use of exhaled humidity in both dry and heated humidified circuits. Proximal nebulizer placement yielded higher doses than distal placement under high settings in dry circuits without exhaled humidity, but this difference was diminished or absent when exhaled humidity or heated humidification were introduced. Bias flow and adapter type had minimal impact on inhaled dose, except in specific conditions under dry circuit without exhaled humidity. Conclusions: In dry circuits without exhaled humidity, aerosol delivery was substantially affected by ventilator settings and nebulizer placement, whereas bias flow and circuit adapter types had no notable impact. However, the effects of ventilator settings and nebulizer placement diminished in circuits with exhaled humidity or heated humidification.