Conclusions
Deep sternal wound infection (DSWI) after cardiac surgery is known to be associated with an increased length of stay, readmission and mortality. Perrault et. al. recently reported outcomes in 5,198 patients enrolled in a prospective study evaluating infections after cardiac surgery and their effect on readmissions and mortality for up to 65 days after cardiac surgery. The cumulative incidence of DSWI (termed mediastinitis in this report) was 0.79% and the median time to diagnosis of infection was 20.6 days. Readmission rates and mortality were five times higher in the mediastinal infection group.
Admitting that DSWI occurs and has been relatively resistant to quality improvement initiatives, we sought to examine outcomes after treatment for DSWI after cardiac surgery. The main findings of our study are that overall survival with our surgical approach to these infections is relatively good, and that those diagnosed with DSWI early and those who have failed initial medical management have increased mortality. As a tertiary referral center, almost half of the subjects in the study were transferred to our institution after their index cardiac surgical procedure and our general management approach is to be surgically aggressive with these infections given the known increased mortality risk in this population.
The overall survival in this cohort of patients was 93% and 81% at 1 and 5 years, suggesting that our operative approach results in acceptable outcomes. These findings of survival after treatment of DSWI are consistent with other reports. Jones et. al. reported a 8.1% 20 years mortality rate in 409 patients undergoing flap coverage of DSWI[11], while Baillot et. al. reported a 15 years review of 88% three years survival of 124 patients undergoing primary negative pressure wound therapy as treatment for DSWI[10]. Others have reported similar results with a variety of treatment modalities[8,13-16].
Risk factors for increased mortality after development of a DSWI in the overall cohort included early diagnosis of DSWI (within 30 days of index cardiac procedure) and attempted medical management. The significant finding of attempted medical management is not entirely surprising given that by study design we only included those patients who had undergone surgical procedures for the DSWI. Therefore, we do not know the true risk of failed medical management of DSWI at our institution as patients managed successfully with medical therapy alone, are not included in this analysis.
The role of timing of diagnosis of DSWI was investigated further by comparing outcomes in those diagnosed early (<30 days) and late (≥30 days) with DSWI after index cardiac procedure. Those with an early diagnosis of DSWI were more likely to be male, more likely to be smokers, and more likely to have elevated glycated hemoglobin levels. After developing propensity scores from a multivariable logistic model to predict differences in baseline characteristics between the two group, male sex, smoking and a positive wound culture were significantly more common in the early diagnosis group. Propensity adjusted Cox proportional hazard modeling demonstrated that early diagnosis of DSWI and an initial attempt at medical management were strongly associated with mortality (hazard ratio 7.48, 95% CI 1.38-40.4, p=0.019 and hazard ratio 7.76, 95% CI 1.67-35.9, p=0.009, respectively), and that this effect was independent of the initial operation (flap or negative pressure wound therapy) or whether any flap was eventually performed.
Early onset infection was more common in male patients, smokers, and those with a positive wound culture while female sex and the requirement of an urgent operation was more common in late onset infection. After adjusting for differences between both groups, those with early onset deep sternal wound infection had higher mortality, likely reflecting a greater degree of aggressiveness of these infections.
These findings support our general philosophy that early aggressive treatment of these infections is optimal. The results suggest that those with early onset infections would perhaps benefit from early aggressive surgical management of DSWI. This general approach is also advocated by others, as Sears et. al. recently demonstrated in a national database study that delayed flap closure for DSWI is associated with increased mortality[8].
Limitations to our study should be acknowledged. First, the retrospective nature of the study limits the ability to draw conclusions regarding causality. Second, our study might be underpowered to draw definitive conclusions. Lastly, the timing and surgical approach undertaken are not standardized and are subject to surgeon preference, reflecting daily clinical practice.
In summary, these results suggest that the early onset of DSWI is associated with increased mortality and that a high index of suspicion, early diagnosis, and aggressive treatment of this devastating complication after cardiac surgery can results in improved outcomes.