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Ann Thorac Surg 2005;80:1270-1275
© 2005 The Society of Thoracic Surgeons
a Department of Cardiothoracic Surgery, Lund University Hospital, Lund, Sweden
b Department of Internal Medicine, Lund University Hospital, Lund, Sweden
Accepted for publication April 5, 2005.
* Address reprint requests to Dr Sjögren, Department of Cardiothoracic Surgery, Heart and Lung Division, Lund University Hospital, SE-221 85 Lund, Sweden (Email: johan.sjogren{at}thorax.lu.se).
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Abstract |
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 Top Abstract IntroductionPatients and MethodsResultsCommentAcknowledgmentsReferences |
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METHODS: Forty-six patients were treated for mediastinitis, with vacuum-assisted closure but without additional tissue flaps, after isolated coronary bypass grafting between January 1999 and September 2004. During this period, 4,781 patients underwent isolated coronary bypass grafting without mediastinitis. Actuarial survival was compared with the log-rank test. Univariate and multivariate analysis were used to identify risk factors for mediastinitis.
RESULTS: There was no difference in early or late survival between the mediastinitis group treated with vacuum-assisted closure and the control group (p = not significant). The survival at 1, 3, and 5 years was 92.9% ± 4.0%, 89.2% ± 5.2%, and 89.2% ± 5.2%, respectively, in the vacuum-assisted closure group; and 96.5% ± 0.3%, 92.1% ± 0.5%, and 86.9% ± 0.8%, respectively, in the control group. Diabetes mellitus, low left ventricular ejection fraction, obesity, renal failure, and three-vessel disease were identified as risk factors for developing mediastinitis.
CONCLUSIONS: This study suggests that patients with vacuum-assisted closure treated mediastinitis may have similar long-term survival as patients without mediastinitis after coronary artery bypass grafting. The independent risk factors identified were similar to those found in previous studies. Our data support that vacuum-assisted closure therapy minimizes the negative effects of mediastinitis on late survival after coronary artery bypass grafting.
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Introduction |
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TopAbstractIntroductionPatients and MethodsResultsCommentAcknowledgmentsReferences |
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The vacuum-assisted closure (VAC) technique is a relatively new modality in wound-healing management. Local application of negative pressure to a wound results in improved tissue blood flow and increased granulation tissue formation [13, 14]. We have used the VAC technique without additional tissue flaps for post-sternotomy mediastinitis at our department since 1999.
The aim of the present study was to compare the long-term survival of patients with VAC-treated mediastinitis after isolated coronary bypass surgery with that of patients undergoing isolated coronary bypass surgery without mediastinitis. We believe this comparison has not been made before. Furthermore, we also evaluated several preoperative and perioperative variables with univariate and multivariate analysis to identify predictors for developing mediastinitis after CABG.
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Patients and Methods |
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TopAbstractIntroductionPatients and MethodsResultsCommentAcknowledgmentsReferences |
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Preoperative, perioperative, and postoperative data were collected in the department database in a prospective manner and 20 variables were selected for analysis (Table 1). No patient with previous open heart surgery was included in the study. The medical records of all patients showing postoperative mediastinitis were also reviewed retrospectively. Patients without post-sternotomy mediastinitis were referred to as the control group. The European System for Cardiac Operative Risk Evaluation (EuroSCORE), an established European system for risk stratification in cardiac surgery, was calculated for each patient [16]. Furthermore, the ACC/AHA mediastinitis score, published in the American College of Cardiology/American Heart Association Guidelines for CABG Surgery, was calculated [17].
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The patients were also classified according to the criteria proposed by El Oakley and Wright [19]. Type I is mediastinitis within 2 weeks after operation in the absence of risk factors. Type II is mediastinitis presenting at 2 to 6 weeks after operation in the absence of risk factors. Type III A is mediastinitis type I in the presence of one or more risk factors. Type III B is mediastinitis type II in the presence of one or more risk factors. Type IV A is mediastinitis type I, II, or III after one failed therapeutic trial. Type IV B is mediastinitis type I, II, or III after more than one failed therapeutic trial. Type V is mediastinitis presenting for the first time more than 6 weeks after operation.
Follow-Up
The protocol for the present study was approved by the Ethics Committee for Clinical Research at Lund University, Sweden. Follow-up was performed in November 2004 and included a total of 12 898 patient-years (mean, 2.7 ± 1.7; range, 0 to 5.8). No patient was lost to follow-up. The long-term mortality data during follow-up was provided from the National Board of Health and Welfare.
Statistical Analysis
Continuous variables are expressed as means ± SD. Categorical variables are presented as absolute numbers in addition to percentages. Univariate analysis for continuous variables was conducted with Student's t test or the Mann-Whitney U test. Categorical variables were analyzed with the 
2 test, except when expected frequencies were lower than 5, when Fisher's exact test was used. Multivariate analysis was performed using stepwise logistic regression to determine independent predictors of mediastinitis. The inclusion criterion for the full model was p less than 0.2, and the limit for stepwise backward elimination was p less than 0.1. Survival was plotted using the Kaplan-Meier method for all patients surviving 3 days after surgery. Fifty-two patients in the control group, who died during the first 3 postoperative days, were not included in the Kaplan-Meier analysis in an attempt to exclude patients not at risk from mediastinitis [20]. No patient in the mediastinitis group was diagnosed with mediastinitis before 4 days after surgery. The log-rank test was used to compare the difference in survival between the two groups. Cox's proportional hazard analysis was used to risk adjust the Kaplan-Meier survival curve for differences in EuroSCORE [21]. Statistical analysis was performed, and graphs were plotted with the Intercooled Stata version 8.2 statistical package (Stata Corporation, College Station, Texas). A p value less than 0.05 was considered statistically significant.
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Results |
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TopAbstractIntroductionPatients and MethodsResultsCommentAcknowledgmentsReferences |
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There were 4 late deaths (8.7%) in the VAC-treated mediastinitis group during follow-up, but no patient died within 90 days after surgery. None of the deaths in the VAC group was related to the sternal infection: 1 patient died of heart failure, 1 patient died of a cerebrovascular incident, 1 patient died of chronic obstructive pulmonary disease, and 1 died of acute pancreatitis. There were 394 deaths (8.2%) among the patients without mediastinitis during follow-up. The annual incidence of death in the VAC group and the control group is presented in Table 2.
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The results of the univariate analysis of risk factors are presented in Table 1. The patients with mediastinitis were more often obese (47.8% versus 19.1%; p < 0.001) and in New York Heart Association (NYHA) class III/IV (60.9% versus 43.7%; p = 0.02) compared with the control group. Diabetes mellitus was more common among patients with mediastinitis (23.9% versus 6.6%; p < 0.001), as was heart failure (30.4% versus 14.3%; p = 0.004), low ejection fraction (21.7% versus 7.9%; p = 0.003), preoperative renal failure (13.0% versus 1.9%; p < 0.001), and preoperative dialysis (4.3% versus 0.7%; p = 0.05). Furthermore, the mediastinitis group included a higher percentage of patients with three-vessel disease (93.5% versus 64.8%; p < 0.001) and a significantly longer procedure time (216 ± 47 versus 197 ± 50 min; p = 0.005).
The multivariate analysis identified diabetes mellitus, left ventricular ejection fraction less than 30%, obesity (body mass index >30), preoperative renal failure, and three-vessel disease as significant risk factors for developing mediastinitis (Table 3).
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Comment |
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TopAbstractIntroductionPatients and MethodsResultsCommentAcknowledgmentsReferences |
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Several studies have suggested that mediastinitis is a strong predictor for poor long-term survival after CABG [2–7]. Braxton and coworkers [8] demonstrated in a large study including 36,078 patients after isolated CABG that actuarial survival after 10 years was 39% among patients with mediastinitis and 70% among patients without mediastinitis. Furthermore, the risk of late mortality was almost twice as high in patients suffering from mediastinitis, even when patients who died within the first 6 months after surgery were excluded [8]. Milano and colleagues [4] have suggested that mediastinitis may cause negative long-term effects on several organs such as the heart and kidneys. Theoretically, a massive immunologic response during a prolonged period of infection may cause adverse effects on bypass grafts.
In previous studies, reporting poor long-term survival after mediastinitis, several conventional wound-healing techniques were used. There is no general consensus regarding the appropriate surgical approach in mediastinitis after open-heart surgery. A commonly accepted wound-healing approach is delayed wound closure including reconstruction with omentum or pectoral flaps [22, 23]. However, there are disadvantages, including additional surgical trauma and late flap-related complications such as pain, weakness, and hernias [10, 24, 25]. Surgical revision with rewiring or closed irrigation offers an expeditious procedure with a closed wound and a stable chest. However, several groups have reported a relatively high rate of therapy failure with these techniques [9, 11, 12, 26]. Therapeutic failure during post-sternotomy mediastinitis treatment is known to aggravate an already difficult situation, and often results in increased early death [27]. Furthermore, ineffective wound management may be harmful, not only in the short term, but also in a longer perspective.
Vacuum-assisted closure is an alternative wound-healing strategy in post-sternotomy mediastinitis and recent studies have reported promising results [28–32]. During the application of this topical negative pressure technique several advantages of conventional treatment are achieved. Vacuum-assisted closure provides an isolated wound with effective drainage in addition to sternal stabilization. This negative pressure system has been demonstrated to stimulate granulation tissue formation [13] and increase the blood flow in adjacent tissue [14]. Furthermore, the negative pressure approximates the sternal wound edges, and the polyurethane foam provides a mass filling effect in the mediastinum without establishing an additional wound in an infected patient, namely, omental or pectoral flap surgery.
The present study demonstrate no difference in long-term survival between patients with VAC-treated mediastinitis and patients without mediastinitis even if patients who died within the first 3 postoperative days were excluded from the control group (Fig 1A). In general, patients suffering from postoperative mediastinitis demonstrated a higher level of comorbidity preoperatively. The univariate analysis showed that patients with mediastinitis were more likely to be obese, and to suffer to a higher extent from diabetes, heart failure, lower ejection fraction, preoperative renal failure, preoperative dialysis, and three-vessel disease than patients without mediastinitis (Table 1). The mediastinitis group also had a longer procedure time and a higher NYHA class when compared with the patients without mediastinitis. In order to minimize effects due to baseline differences, an adjustment in preoperative EuroSCORE was performed although patients suffering from mediastinitis had a significantly higher preoperative EuroSCORE (6.9 versus 5.2; p = 0.001). The EuroSCORE was used since it has been demonstrated to be a predictor of early and late mortality after coronary bypass grafting [33, 34]. However, no difference in long-term survival was observed between the two groups after the adjustment was made (Fig 1B).
The multivariate analysis identified obesity as an independent risk factor (Table 2). Other studies have previously found obesity to be a risk factor for developing post-sternotomy mediastinitis [35, 36]. The mechanism by which obesity leads to this complication is poorly understood but it is likely to be multifactorial. Perioperative antibiotics may be poorly distributed in adipose tissue, as suggested by Milano and coworkers [4]. Furthermore, it may be difficult to diagnose mediastinitis in obese patients during the early phase of the infection. We also found diabetes mellitus to be a risk factor for mediastinitis. This finding is in line with previous reports [1, 2]. Elevated blood glucose levels may impair wound healing, and the use of continuous intravenous insulin has been shown to significantly reduce the incidence of deep sternal wound infection in diabetic patients [37]. A low ejection fraction (< 30%) of the left ventricle was also demonstrated to be a significant risk factor for infection. A reduced ejection fraction is included as a variable in the mediastinitis score proposed by the Northern New England Cardiovascular Disease Study Group [17]. Other studies have identified high NYHA class as a predictor of mediastinitis [4, 38]. Furthermore, preoperative renal failure (creatinine >2.27 mg/dL) was found to be an independent risk factor for developing post-sternotomy mediastinitis. This probably reflects, at least to some extent, a general atherosclerotic condition that may predispose these patients to poor wound healing. Finally, we identified an increased risk of mediastinitis when coronary atherosclerosis affected all main coronary vessels. Again, it is not clear what the true primary cause is. Three-vessel disease probably reflects general vascular pathology leading to longer procedure times, and length of surgery has been demonstrated in previous studies to be a risk factor for post-sternotomy mediastinitis [4].
In conclusion, the present study suggests similar long-term survival between patients with VAC-treated mediastinitis and patients without mediastinitis undergoing isolated CABG. This finding is in contrast to previous reports on long-term survival after mediastinitis; however, in these previous studies, conventional mediastinitis treatment was used. One limitation in the present study is the rather limited sample size in the mediastinitis group, and therefore conclusions regarding survival should be made with caution. We believe that our results are due to the use of VAC therapy without the use of additional soft tissue flap surgery. This approach combines several wound-healing principles and may counteract the negative effects on late survival. In the present work, we also identified independent risk factors similar to those found in previous studies. In our opinion, additional attention should be paid to obese patients, especially when other preoperative comorbidity such as diabetes mellitus, renal failure, low ejection fraction, or extensive coronary artery disease are present.
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Acknowledgments |
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TopAbstractIntroductionPatients and MethodsResultsCommentAcknowledgmentsReferences |
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References |
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TopAbstractIntroductionPatients and MethodsResultsCommentAcknowledgmentsReferences |
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