[The impact of gastric colonization on the pathogenesis of ventilator-associated pneumonia]

To investigate the risk factors for gastric bacterial colonization and its role in the endogenous pathogenesis of ventilator-associated pneumonia (VAP).

The type and concentration of gastric colonized bacteria and its relationship with the time when samples were collected, and with the type and occurrence order of the pathogens detected in samples from lower respiratory tract after the onset of VAP were analyzed dynamically in the patients with tracheal-intubation or tracheotomy in intensive care unit (ICU).

(1) The isolation rate of colonized bacteria in gastric cavity was associated with the pH of gastric juice. When the pH of gastric juice was > 4, the isolation rate of Gram-negative bacilli (GNB) in gastric cavity markedly increased, achieving 52.5% in VAP group, and the incidence of VAP was higher (P = 0.017). The pH value of gastric juice was positively correlated with the logarithmic concentration of GNB in gastric cavity (P = 0.001). (2) As the duration of intubation prolonged, the isolation rate of enterobacteriaceae in VAP group increased, which was 45.2% on the fifth day of intubation. In contrast, the isolation rate in non-VAP group was 11.1% (P < 0.01). (3) The colonization of enterobacteriaceae in gastric cavity was 1 - 2 days earlier than that in oropharynx. The order was statistically significant (P = 0.015). (4) The reverse order of stomach-pharynx-lower respiratory tract colonization was found in 12 cases of the total 52 VAP patients and the order of stomach to lower respiratory tract colonization was found in 3 cases.

(1) The pH value of gastric juice proved to be the major factor which influenced the colonization of bacteria especially GNB in gastric cavity. (2) The gastric cavity was probably a colonization place of GNB especially enterobacteriaceae. (3) The enterobateriaceae in gastric cavity tended to colonize reversely to oropharynx. (4) The phenotypic analysis of the pathogens showed that the reverse stomach-pharynx-lower respiratory tract infection route existed in VAP patients.