Risk factors for sternal wound infection and mid-term survival following coronary artery bypass surgery

Abstract

Objective: To identify risk factors for sternal wound infection following coronary artery bypass surgery (CABG), and to compare early and mid-term survival outcome.

Methods: Data were prospectively collected for 4228 patients who underwent CABG surgery between April 1997 and March 2001. One hundred and nine (2.6%) patients developed sternal wound infection. We used logistic regression to identify independent risk factors associated with post-operative sternal wound infection. Patient records were linked to the National Strategic Tracing Service, which records all deaths in the UK, to establish current vital status. Deaths occurring over time were described using Kaplan-Meier techniques. To control for differences in patient characteristics, we used Cox proportional hazards analysis to calculate adjusted hazard ratios (HR) and 95% confidence intervals (CI).

Results: The results of the logistic regression analysis found that the independent predictors of sternal wound infection were obesity (odds ratio (OR) 2.0; P<0.001), New York Heart Association class >/=3 (OR 1.6; P=0.022), use of bilateral internal mammary arteries (OR 3.2; P<0.001), increasing number of grafts (OR 1.5; P<0.001), re-exploration for bleeding (OR 3.1; P=0.011), and increased duration of mechanical ventilation (for every 10 h (OR 1.12; P<0.001)). Three hundred and forty one (8.1%) deaths occurred during the study period with mean follow up of 3.2+/-1.3 years. The crude HR of mid-term mortality for sternal wound infection patients was 2.51 (95% CI 1.59-3.94, P<0.001). After adjustment for pre, intra and post-operative factors, the adjusted HR of mid-term mortality for sternal wound infection patients was 1.64 (95% CI 1.03-2.61, P=0.037). The adjusted freedom from death for sternal wound infections at 30 days, and 1, 2 and 4 years was 96.8, 93.7, 91.4 and 86.7%, respectively, compared with 98.1, 96.1, 94.7 and 91.7% for patients without sternal wound infections.

Conclusions: In conclusion, we have identified risk factors for sternal wound infection, many of which are modifiable. We have also shown that there is a significant increase in mortality in patients with sternal wound infection during a 4-year follow-up period after CABG.