Role of colonization of the upper intestinal tract in the pathogenesis of ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) is the most frequent infection in mechanically ventilated patients. Colonization of the gastrointestinal tract, especially the stomach, is believed to be important in the pathogenesis of VAP. However, the literature on this topic is full of contradictory evidence. In the present review, we critically assess the existence and importance of the gastropulmonary route of colonization in the pathogenesis of VAP, and we analyze the differences between studies that show different results. Several preventive regimens (e.g., the use of sucralfate for stress ulcer prophylaxis and modulation of enteral feeding) have been used to prevent gastric colonization and decrease the incidence of VAP. However, none of these regimens has been demonstrated to be unequivocally beneficial. Moreover, recent analyses of the sequences of colonization in patients who develop VAP suggest that gastric colonization may be less important in the pathogenesis of VAP than has been assumed. As a result, the impact of other routes of colonization such as cross-colonization or transfer of rectal bacteria via the skin or other vectors to the respiratory tract may have been underestimated. Knowledge of the relative importance of each of these possible routes of colonization is essential for developing effective measures to prevent VAP.