Eastern Cardiothoracic Surgical Society

Should Gram-Negative Antibiotic Prophylaxis Be Considered for Coronary Artery Bypass Grafting?
Charles M. Wojnarski1, Yakov Elgudin2, Joseph Rubelowsky2, Diana Whittlesey2, Brigid Wilson2, Curtis Donskey2, Brian Cmolik2, 1University Hospitals Cleveland Medical Center, Cleveland, OH, 2Louis Stokes Cleveland VA Medical Center, Cleveland, OH

OBJECTIVE: Identify changes in microbiology of mediastinitis over the last decade and perform a modern survival analysis in patients with mediastinitis.

METHODS: From January 2006 to December 2015, 45,323 consecutive patients underwent CABG at 83 medical centers. The VA nationwide administrative database was queried to identify patients with postoperative mediastinitis and obtain patient-level data. Simple descriptive statistics and multivariable logistic regression were used to analyze microbiologic data and identify risk factors for infection. Cox's proportional hazard model identified predictors of long-term survival.

RESULTS: During the study period, 348 patients (0.78%) developed postoperative mediastinitis. Of patients with microbiologic data, 75.5% infections (n=188) were caused by gram-positive and 24.5% (n=61) gram-negative organisms. There was a linear trend toward decreased incidence of gram-positive mediastinitis (1.3%/year, p=0.04); largely driven by a decrease in MRSA mediastinitis (1.6%/year, p=0.03). Patients with mediastinitis did not have increased 30-day mortality (2.0% vs. 1.9%, p=0.9); however, had worse long-term survival compared to non-infected patients (p<0.0001). Gram negative mediastinitis occurred earlier than gram positive mediastinitis (median 15.0 vs. 25.0 days, p<0.0001). Multivariable analysis identified history of COPD as a risk factor for gram-negative mediastinitis (OR 1.92, p=0.05). Gram-positivity had no effect on long term survival (p=0.61).

CONCLUSIONS: Gram-positives remain the predominant organisms responsible for mediastinitis after CABG, although incidence has decreased over the last decade. Gram-negative bacteria are responsible for 1 in 4 cases of mediastinitis. Prophylactic gram-negative peri-operative antibiotics should be considered in patients with COPD in addition to current guidelines to prevent gram-negative mediastinitis.