Aerosol dispersion in a ventilator circuit: towards a model for enhancing our understanding of ventilator-associated pneumonia

Background Patients receiving mechanical ventilation for more than 48 hours are at risk for developing ventilator-associated pneumonia (VAP). Methods We investigated aerosol flow in a ventilator circuit attached to test lungs to better understand how airflow dynamics in ventilator tubing can contribute to the pathogenesis of VAP. The ventilator was operated so that the lungs cyclically inflated and deflated. Aerosolized saline was used as a surrogate for bioaerosols and was generated in the circuit with an aerosol generator attached to the tubing below an endotracheal cuff that sealed an endotracheal tube at the opening of the lungs. We used a particle collector and analyzer attached to the circuit approximately two feet from the opening of the lungs to determine whether aerosols flowed into the tubing. Results We detected significant levels of aerosolized particles (P <0.05) that traveled retrogradely into the ventilator circuit. The highest nozzle pressure tested, 13 hPa, produced mean 0.5, 0.7 and 1.0 m aerosol levels of 24 ±5, 10±4 and 8±3 particles/ft 3, respectively. The lowest nozzle pressure tested, 10 hPa, produced mean 0.5, 0.7 and 1.0 m aerosol levels of 14 ±5, 4 ±2, and 3 ±2 particles/ft3. Conclusions Aerosolized material that enters the circuit near the endotracheal cuff travels into the ventilator tubing during mechanical ventilation. Our results suggest that infectious material could travel a similar route and contaminate the air in the ventilator circuit which then enters the patient. Keywords: ventilator-associated pneumonia, bioaerosol, aerosol, contamination, ventilator circuit