336 Gram-negative bacilli: a new independent risk factor of mortality after mediastinitis

Background Postoperative mediastinitis after cardiac surgery is associated with morbidity and mortality. The aim of this study was to identify risk factors for mortality after a diagnosis of post-operative mediastinitis. Methods Retrospective cohort study including all patients with post-operative mediastinitis throughout the 2000–2008 period, hospitalized in the Department of Intensive Care Unit (ICU) of the Hopital Europeen Georges Pompidou (HEGP, Paris, France) and the Centre Cardiologique du Nord (CCN, Saint-Denis, France). Post-operative mediastinitis was defined as an organ-space infection involving the mediastinum and necessitating debridement. The therapeutic management was comparable in both centers. Using univariate and multivariate analyses, risk factors of mortality during hospitalization were identified. Results 310 patients were included (mean age 65 ± 12 years, 76% men). Logistic Euroscore was 7.7 ± 9.3. The mortality rate was 21% among the patients with mediastinitis. In the multivariate analysis, the independent risk factors for mortality were age (odds ratio, 1.48; 95% confidence interval, 1.42–1.54), presence of Gram-negative bacilli (GNB) (odds ratio, 2.34; 95% confidence interval, 1.06–5.15), presence of Methicillin-resistant Staphylococcus aureus (MRSA) (odds ratio, 5.51; 95% confidence interval, 1.43–21.25), renal insufficiency before debridement (odds ratio, 4.46; 95% confidence interval, 1.36–14.56), clinical status score (including mechanical ventilation required still on day 3 and/or amines required in ICU after debridment) (odds ratio, 29.03; 95% confidence interval, 11.26–74.82) Conclusions Pathogens are one of the major factors of post-operative mediastinitis mortality. GNB as MRSA are associated with high mortality. These results emphasize the importance of antimicrobial prophylaxis with a large spectrum as second generation cephalosporin.