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.