Ventilator-associated pneumonia (VAP) is a diffuse polymicrobial and dynami
c process, with heterogeneous distribution of lesions, showing different de
grees of histological evolution predominating in the dependent lung zones,
in which microbiology and histology can be dissociated. This might explain
why blind endobronchial techniques to collect respiratory secretions have s
imilar accuracy compared to visually guided samples, explaining the difficu
lties in validating any methods for its diagnosis, In the clinical setting
the association of acute lung injury (ALI) and pneumonia is controversial.
However, it is rare to detect diffuse alveolar damage (DAD) in absence of h
istological signs of pneumonia, probably evidencing that ALI favors the dev
elopment of pneumonia, Histopathologically, it is difficult to distinguish
initial and resolution phases of DAD from pneumonia and vice versa, On the
other hand, there is a clear relationship between antimicrobial treatment a
nd the decreased lung bacterial burden which strengthens the importance of
distal airway sampling before starting antibiotic therapy.