Lactulose decreases pH of colon contents and can thus inhibit the overgrowth of pathogenic strains. In our study the impact of lactulose on microbial colonisation of critically ill patients was investigated. Forty-eight mechanically ventilated patients with no signs of pneumonia on admission were recruited into the prospective double-blind randomised study (15 ml lactulose versus saline q.i. d administered into the stomach). Gastric and oropharyngeal contents, tracheal aspirate and rectal swab were taken on admission and then at 3 day intervals. The concentration of pathogens > 105/ml was considered significant. Thirty-eight patients (15 given lactulose and 23 placebo) were mechanically ventilated > 5 days and were further analysed. The colonisation of stomach and trachea were not statistically significant between the groups. The incidence of ventilatory pneumonia also failed to differ (40 and 35 %, respectively). The so called gastro-pulmonal route of infection was not confirmed. Oropharynx seems to be a major source of tracheal colonisation.

        Key words: ventilator associated pneumonia - lactulose - nasocomial infection - intensive care