Obesity and Preoperative Anaemia As Independent Risk Factors for Sternal Wound Infection after Coronary Artery Bypass Graft Surgery with Pedicled (Non-Skeletonized) Internal Mammary Arteries: the Role of Thoracic Wall Ischemia?

Purpose: Obesity remains statistically associated with coronary artery disease, for which coronary artery bypass graft surgery (CABG) remains the standard of care. However, obesity is also associated with sternal wound infection (SWI) which is a severe complication of CABG despite advances in surgery and in infection prevention and control. Strategies to reduce the incidence of SWI are still being investigated, and we therefore conducted a retrospective study to revisit factors other than obesity associated with SWI after CABG. Patients and Methods: Data were extracted from the medical records of 182 patients who underwent elective on-pump CABG using one or both pedicled internal mammary artery grafts in Reims University Hospital between May 2015 and May 2016. All preoperative or perioperative variables with a p value<0.10 in univariate analysis were entered into a stepwise logistic regression model. Results: Among the 182 patients (145 male (79.6%), median age 68.0 [45.0-87.0] years), 138 (75.8%) underwent CABG using bilateral internal mammary artery grafts. Median BMI was 27.7 [18.7-50.5] kg/m 2 , and there were 51 (28.0%) and 79 (43.4%) patients with obesity and overweight, respectively. Twenty-three out of the 182 patients (12.6%) developed SWI. In-hospital mortality was not statistically different between patients with and without SWI but the median length of stay was (6.0 [2.0-38.0] versus 5.0[3.0-21.0] days in the intensive care unit, p=0.03, and 26.0 [9.0-134.0] versus 9.0 [7.0-51.0] days in hospital, p<0.0001). Obesity and preoperative anaemia were independently associated with SWI, as was the number of red blood cell (RBC) units transfused (OR 14.61 [2.64-80.75], OR 4.64 [1.61-13.34] and OR 1.27 [1.02-1.58], respectively). Conclusion: The independent association of SWI with the number of RBC units transfused and the existence of preoperative anaemia and obesity suggests a mechanism of thoracic wall ischemia in SWI after CABG, thus leaving insufficient perfusion of the thoracic wall in patients with obesity. Medical strategies are warranted to try to prevent this costly complication.