The pathogens that cause VAP are able to overcome
the mechanical, hormonal, and/or cellular
defenses of the body, thereby invading, colonizing,
and establishing an infection within the lower part
of the respiratory tract. Microbial access to the otherwise
sterile lower part of the respiratory tract can
occur via 4 mechanisms: aspiration of pathogencontaining
oropharyngeal secretions from the gastric
cavity or sinuses, dissemination
of organisms from a contiguous
area such as the pleura, inhalation
of contaminated aerosols after the
use of respiratory therapy devices,
and hematogenous spread from
remote infection sites to the lung