Lack of impact of selective digestive decontamination on Pseudomonas aeruginosa ventilator-associated pneumonia: benchmarking the evidence base

Background: The selective digestive decontamination (SDD) component antibiotics have activity against Pseudomonas aeruginosa, an important ventilator-associated pneumonia (VAP) isolate. Evaluating the relationship between the anti-pseudomonal activity of SDD towards its VAP prevention effect is complicated by postulated indirect effects of SDD mediated in the concurrent control groups. The objective here is to address these effects through a benchmarking analysis of the evidence base. Methods: Forty-eight observational studies of VAP incidence and 43 interventional studies of SDD and other methods of VAP prevention were sourced from 10 reviews. The P. aeruginosa isolate proportion (P. aeruginosa-IP) data were summarized by meta-analysis using random effects methods. The mode of VAP diagnosis, proportion of trauma admissions and the intervention method under study were examined in meta-regression models as potential group-level predictors of P. aeruginosa-IP. Results: The mean P. aeruginosa-IP derived from the observational studies (the benchmark) is 22.3% [95% confidence interval (CI) 19.8%-25.2%] versus 19.6% (95% CI 15.6%-24.4%) and 20.8% (95% CI 14.6%-28.5%) for concurrent control groups and intervention groups of SDD studies, respectively. In the meta-regression models, the proportion of trauma admissions is negatively correlated with P. aeruginosa-IP, whereas membership of neither a concurrent control nor intervention group of an SDD study is negatively correlated. Conclusions: There is no evidence for either direct or indirect effects of SDD on P. aeruginosa-IP that could account for the profound effects of SDD on VAP incidence.