Manipulation of the microbiome in critical illness—probiotics as a preventive measure against ventilator-associated pneumonia

OBJECTIVE: To describe the possible modes of action of probiotics and provide a systematic review of the current evidence on the efficacy of probiotics to prevent ventilator-associated pneumonia (VAP) in critically ill patients. METHODS: We conducted an unrestricted search of the English language medical literature. For each individual study, the relative risk of VAP was calculated using the reported primary outcome data. RESULTS: The search identified a total of 72 articles. Eight articles enrolling a total of 1229 patients fulfilled the inclusion and exclusion criteria. In four trials, the investigators were blinded for the intervention, and two trials used an intention-to-treat analysis. Loss to follow-up with regard to the primary endpoint ranged from 0 to 14% in the intervention groups and from 0 to 16% in the control groups. The incidence of VAP expressed as the percentage of studied patients was reported in seven trials. The incidence of VAP ranged from 4 to 36% in the intervention groups and from 13 to 50% in the control groups. The relative risk for VAP ranged between 0.30 and 1.41. Three trials showed a significant difference in favor of probiotic therapy between the intervention and the control groups. CONCLUSIONS: The incidence of VAP tended to be lower in patients treated with probiotics in most trials identified by the systematic search. Due to the heterogeneity of the studies and the low quality of evidence, it remains difficult to draw firm conclusions. The efficacy of preventive probiotics should be studied in more detail in future trials. Application of probiotics for the prevention of VAP seems to be safe with only few side effects reported in the selected trials. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s40635-019-0238-1) contains supplementary material, which is available to authorized users.