Risk factors for mediastinitis following cardiac surgery: the importance of managing obesity.

Mediastinitis is a devastating complication of cardiac surgery. Previous studies have often observed small populations, been retrospective in design, and used a variety of definitions for mediastinitis.To identify risk factors for mediastinitis, and strategies to minimize its incidence.A prospective cohort study of 4883 adult patients who underwent cardiac surgery between October 2003 and February 2009, comparing pre- and peri-operative risk factors, microbial aetiology, requirement for re-admission, length of stay and mortality between patients with and without mediastinitis.Ninety (1.8%) patients were diagnosed with mediastinitis. Microbial aetiology was defined for 75 patients. Staphlyocococcus aureus was the most common isolate (30 episodes; 15 due to meticillin-resistant S. aureus). Univariate analysis revealed the following pre-operative factors associated with mediastinitis: age; body mass index; diabetes; modified logistic European System for Cardiac Operative Risk Evaluation score; urgent admission; and longer pre-operative stay (P < 0.05). Associated peri-operative factors were: combined coronary artery bypass grafting plus aortic valve replacement; longer aortic cross-clamp time; and longer cardiopulmonary bypass time (P < 0.005). Multi-variate analysis revealed that higher body mass index, combined coronary artery bypass grafting plus aortic valve replacement, and older age were associated with mediastinitis (P < 0.05). Mediastinitis was associated with re-admission to hospital, longer inpatient stay and reduced long-term survival (P < 0.05).Mediastinitis is associated with worse short-term outcomes (re-admission, length of stay) and reduced long-term survival. Obesity is the only modifiable pre-operative risk factor for mediastinitis. It may be possible to reduce risk through pre-operative weight loss programmes before elective surgery.