(p. 530) Pneumonia 

Airway colonization, ventilator-associated tracheobronchitis (VAT), and hospital-acquired (HAP) and ventilator-associated pneumonia (VAP) are three manifestations having the presence of micro-organisms in airways in common. Newer definitions have to consider worsening of oxygenation, in addition to purulent respiratory secretions, chest-X rays opacities, and biomarkers of inflammation. Bacteria are the main causes of HAP/VAP. During hospitalization there’s a shift of airway’s colonizing flora from core organisms to enteric and non-fermentative ones. Macro- and micro-aspiration is the most important source of pneumonia. Endotracheal tube secretion leakage is an important source, serving biofilm as a reservoir. Exogenous colonization is infrequent, but it may contribute to cross-infection with resistant species. Prevention of VAP can be achieved by implementing multidisciplinary care bundles focusing on oral/hand hygiene and control of sedation. Pneumonia develops when micro-organisms overwhelm host defences, resulting in a multifocal process. Risk and severity of pneumonia is determined by bacterial burden, organism virulence and host defences. Innate and adaptive immune responses are altered, decreasing clearing of pathogens. Some deficits of the complement pathway in intubated patients are associated with increased risk for VAP and higher mortality. Micro-arrays have demonstrated specific different immunological signatures for VAP and VAT. Early antibiotic therapy is associated with a decrease in early HAP/VAP incidence, but selects for MDR organisms. Attributable mortality is lower than 10%, but HAP/VAP prolongs length of stay, and dramatically increase costs and use of health care resources.