Pathophysiology of VAP: In healthy individuals multiple mechanisms work together to fight off the development of pneumonia; unfortunately the presence of an ETT as well as the typical clinical circumstances of ICU patients (i.e. sedation, supine positioning, colonization of the oropharynx with pathogenic microorganisms) interfere with these native defense mechanisms and predispose intubated patients to the development of VAP. A clear understanding of the pathophysiology is important to understand the targets of VAP-prevention strategies