Mediastinitis after coronary artery bypass grafting risk factors and long-term survival

Ivar Risnes, Michael Abdelnoor, Sven M Almdahl, Jan L Svennevig
Annals of Thoracic Surgery 2010, 89 (5): 1502-9

BACKGROUND: Mediastinitis is a severe complication of coronary artery bypass grafting. The aim of the present study was to determine incidence of mediastinitis, its risk factors, and its effect on early and long-term survival.

METHODS: The study has a dual design, a case-control, and a retrospective cohort, using a source population of 18,532 consecutive patients who underwent coronary artery bypass grafting from January 1989 to December 2000. The closing date was February 1, 2008. Median follow-up was 10.3 (range 8.1 to 18.9) years. Patients with mediastinitis were compared with a random control group without mediastinitis issued from the same source population in a ratio 1:4. The crude effect of mediastinitis was estimated using rate ratio and 95% confidence limits. Adjustment for multiconfounders was done with the Cox model. A logistic model was used to pinpoint risk factors of mediastinitis. Calibration and discrimination of a prognostic model was done.

RESULTS: One hundred seven patients (0.6%) developed mediastinitis. Diagnosis was made 12 (9 to 19) days postoperatively. Independent risk factors of mediastinitis using the logistic model were advanced age, male gender, left main stenosis, body mass index 30 kg/m(2) or greater, chronic obstructive pulmonary disease, diabetes, and increased amount of blood transfusion. There was no increased risk of early mortality (odds ratio = 0.58; 95% confidence interval 0.13 to 2.61) (p = 0.48) but there was increased risk of morbidity (intraaortic balloon pump, ventricular and supraventricular arrhythmia, stroke, inotrope, and myocardial infarction). Follow-up had a median observation time of 10.3 years. Survival for patients with mediastinitis was 49.5 +/- 5.0% versus 71.0 +/- 2.2% for controls (p < 0.01). Analysis of specific death causes documented that cardiac deaths were significantly more frequent in mediastinitis patients than in control patients. When controlling for the confounding effect of the other variables (age, cardiopulmonary bypass time, body mass index, chronic obstructive pulmonary disease), the hazard ratio associated with mediastinitis on long-term mortality was 1.59, 95% confidence limits (1.16 and 2.70) (p = 0.003).

CONCLUSIONS: The incidence of mediastinitis in 18,532 patients undergoing coronary artery bypass grafting surgery was low. The major preventable risk factor of mediastinitis was amount of blood transfusion. Mediastinitis had an excess risk of early morbidity and was associated with a significant reduced long-term survival. Most deaths were considered to be cardiac.

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