Ann Thorac Surg 2005;80:957-961
© 2005 The Society of Thoracic Surgeons
Original article: Cardiovascular
Deep Sternal Wound Infection After Cardiac Surgery: Modality of Treatment and Outcome
Franz F. Immer, MD
a
,
*
,
Martina Durrer, MD
a
,
Kathrin S. Mühlemann, MD, PhD
b
,
Dominique Erni, MD
c
,
Brigitta Gahl, MCS
a
,
Thierry P. Carrel, MD
a
a Department of Cardiovascular Surgery, Inselspital, University Hospital, Berne, Switzerland
b Department of Infectious Diseases, Inselspital, University Hospital, Berne, Switzerland
c Division of Plastic Surgery, Inselspital, University Hospital, Berne, Switzerland
Accepted for publication March 7, 2005.
* Address reprint requests to Dr Immer, Department of Cardiovascular Surgery, University Hospital, 3010 Berne, Switzerland (Email: franzimmer{at}yahoo.de).
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Abstract
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BACKGROUND: Deep sternal wound infection is a serious and expensive complication after cardiac surgical procedures. We tried to identify risk factors for failure of vacuum-assisted sternal closure and compare the outcome and long-term quality of life (QoL) with the results obtained after sternal resection and muscle flap.
METHODS: Between January 1998 and December 2003, 5,690 patients underwent cardiac surgical procedures at our institution. Fifty-five patients who had deep sternal wound infection were identified between January 1998 and December 2003. In-hospital data were assessed and the outcome was analyzed. QoL, using the Short Form 36 Health Survey Questionnaire (SF-36), was assessed and an additional questionnaire focused on specific problems.
RESULTS: Overall mortality was 5.4%. Patients with successful vacuum-assisted sternal closure were younger and had fewer cumulative risk factors (chronic obstructive pulmonary disease, bilateral internal mammary artery, obesity, diabetes), than patients in whom secondary closure failed. Quality of life was better among patients with secondary vacuum-assisted closure than among patients with musculocutaneous flap. Independently of the modality of treatment, pain was not a serious problem reported by the patients during the follow-up.
CONCLUSIONS: We conclude that preservation of the sternum should be the principal aim of surgical treatment in patients with deep sternal wound infection. Early diagnosis, aggressive surgical treatment by débridement, and the use of vacuum-assisted systems allows us to achieve a good long-term result with nearly normal QoL. Resection and musculocutaneous flap is a therapeutic option for high-risk patients, providing a safe, effective control of the infection, and it leads to acceptable results in terms of pain control and QoL.
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Introduction
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Deep sternal wound infection (DSWI) after cardiac surgical procedure is a rare but major problem associated with considerable mortality and morbidity [1–7]. Continuous antibiotic irrigation and débridement has been the primary therapeutic option for years, allowing secondary refixation of the sternum [8]. For patients in whom this treatment modality failed, Lee and coworkers [9] described the technique of sternal excision and transposition of the omentum, combined with a primary closure of the wound. The use of a pectoralis major muscle flap [10] has led to a further reduction of mortality in patients suffering from DSWI in the last 20 years [11–13]. In recent years, patients for whom there is high suspicion of osteomyelitis DSWI have been treated at our institution by radical sternectomy and primary musculocutaneous flap reconstruction [14]. The results were very promising, providing definitive control of sternal infection and a reduction of infection-related mortality. Vacuum-assisted closure of DSWI has been available in our institution for the past few years. This new treatment modality helped to decrease the number of patients for sternal resection and musculocutaneous flap because a secondary closure of the sternum could be performed. The present study tried to identify risk factors for failure of vacuum-assisted secondary sternal closure and analyzed outcome and quality of life (QoL) of patients treated with vacuum-assisted closure and compared these results to those of patients who underwent sternal resection and musculocutaneous flap due to vacuum-assisted closure failure. Additionally, a historical group, treated primarily with sternal resection and musculocutaneous flap, has been analyzed and compared with the data of patients being treated with the vacuum-assisted closure system.
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Patients and Methods
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Between January 1998 and December 2003, 5,690 sternotomies were performed in patients undergoing cardiac surgical procedures at our institution. Only patients with DSWI (El Oakley class 2B) were included in the present study. In 55 patients (0.96%) postoperative DSWI was diagnosed based on sternal dehiscence and positive bacteriologic culture of the sternum or the anterior mediastinum. Quality of life studies with the SF-36 have been accepted by the local ethical committee. Patient’s characteristics were analyzed retrospectively and modality of treatment was assessed. According to the treatment modality patients were divided into three groups: group 1 (n = 19) patients were treated with the vacuum-assisted system and underwent successful secondary closure of the sternum; group 2 (n = 19) underwent vacuum-assisted therapy, but secondary closure of the sternum was not possible, requiring secondary sternal excision and musculocutaneous flap; and group 3 (n = 17) is a historical group, treated with sternal excision and primary musculocutaneous flap.
In a few patients, despite the availability of the vacuum-assisted closure system, primary sternal excision and musculocutaneous flap, has been chosen as therapeutic option. In these patients, the decision was based on the poor quality of the sternum (fractured, white aspect, fragile) or on the clinical situation with incontrollable infection and hemodynamic instability. The technique of sternal excision and musculocutaneous flap has been described previously [14]. Vacuum-assisted treatment was performed using the KCI system (KCI, San Antonio, Texas), with a vacuum pressure between 75 mm and 125 mm Hg. Débridement and exchange of the sponge was performed in all patients every 48 to 72 hours in the operation room. Bacteriologic cultures were collected every time patients underwent débridement of the sternal wound. All patients received standardized preoperative intravenous antibiotics (first-generation cephalosporin or vancomyin in case of allergy) within 1 hour of operation and during the next 36 hours. Infectiologists were consulted in every case of DSWI, and antibiotics were applied intravenously at least for 4 to 6 weeks.
For all patients a follow-up was performed and quality of life was assessed with the Short Form 36 Health Survey Questionnaire (SF-36), which is a validated questionnaire to assess subjective QoL [15, 16]. In brief, it consists of 36 short questions mirroring health and QoL in eight different aspects: bodily pain (abbreviated BP, 2 items); mental health (MH, 5); vitality (VT, 4); social functioning (SF, 2); general health (GH, 5); physical functioning (PF, 10); and role functioning, both emotional (RE, 3) and physical (RP, 4). Role functioning reflects the impact of emotional and physical disability on work and regular activity (the patient’s normal everyday role). An additional questionnaire focused on respiratory problems, sternal pain, cosmetic aspects, and long-term satisfaction of the patient with the postoperative result.
Statistical Analysis
Results were analyzed in accordance to the SF-36 manual and missing values replaced using the described algorithm [15, 16]. The SF-36 scores are presented as mean ± SD. A Mann-Whitney U and 
2 test were used for comparison of continuous and nominal variables, respectively. A multivariate logistic regression analysis has been performed in patients from groups 1 and 2, taking into account the factors age, chronic obstructive pulmonary disease (COPD), and diabetes.A p value of less than 0.05 was considered statistically significant. All analyses were performed with StatView 4.1 statistical software package (Abacus Concepts, Berkeley, California).
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Results
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Clinical Data
Patients from group 1 were significantly younger (60.1 ± 11.8 years) than patients from group 2 (66.6 ± 7.2 years) and group 3 (69.5 ± 8.1 years; p < 0.05; Table 1). Three of 55 patients died in the postoperative period, leading to an overall mortality of 5.4%. Two patients died of multiorgan failure—a patient in group 1 and another patient in group 3. The third patient, also in group 3, died of uncontrollable septicemia. Overall in-hospital mortality after cardiac surgical procedures, including emergency interventions, was 2.3% in the same time period for the total collective.
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Table 1. Patient Characteristics, Displayed for Patients From Group 1 (n = 19), Group 2 (n = 19), and Group 3 (n = 17)
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Failure of secondary sternal refixation after vacuum-assisted treatment, revealed that presence of COPD, insulin-dependent diabetes mellitus, older age, and the use of bilateral internal mammary artery were the most important risk factors. Multivariate logistic regression analysis (Table 2) with the factors age, COPD, and diabetes revealed that younger age is the factor that contributes most to the success of vacuum-assisted closure therapy but still failed to be significant at usual p less than 0.05 level. Bacteriologic culture showed the presence of Staphylococcus aureus in the majority of patients. No differences in microbiology were found among the three groups (p = not significant). Postoperative C-reactive protein (CRP) was significantly higher in patients from group 2 (271.0 ± 43.4 at postoperative day [POD] 2 and 301.1 ± 99.1 at POD 3), compared with 168.0 ± 62.6 (POD 2) and 181.7 ± 79.3 (POD 3) in group 3 (p < 0.05)). Patients from group 1 required in the average 4.2 ± 1.5 reoperations, compared with 4.1 ± 1.9 in group 2 and 1.4 ± 0.5 in group 3 (p < 0.05). Time interval between initial operation and diagnosis of DSWI varied among the three groups. Early diagnosis was mainly made in group 1, and delayed diagnosis in group 2 and 3. However, delayed diagnosis in group 2 is due to 1 patient in whom DSWI was diagnosed 902 days after surgery. Not taking into account this patient, diagnosis of DSWI was 2 19.9 ± 10.8 days after surgery in group 2, compared with 17.5 ± 5.1 days in group 1 (p = not significant). Length of stay was significantly longer in patients from group 2, with an average of 89.1 ± 54.4 days, compared with 70.7 ± 28.8 days in group 3 and 51.5 ± 20.8 days in group 1 (Table 1).
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Table 2. Multivariate Logistic Regression Analyis Performed With the Factors Age, COPD, and Diabetes Mellitus for Patients From Groups 1 and 2
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Follow-Up
Average follow-up was similar in patients from groups 1 and 2, with 29.3 ± 20.5 months and 30.8 ± 16.1 months, respectively (p = not significant). Patients from group 3 had a longer follow-up, with an average of 54.3 ± 13.3 months, because they are in the majority in a historical collective. Eleven patients (20%) died during the follow-up. The mortality rate was 5.3% in group 1, 21.1% in group 2, and 41.2% in group 3. Kaplan-Meier survival curves revealed no differences between groups 2 and 3 at the same time extent of follow-up, but survival was significantly better among patients from group 1, compared with survival in groups 2 and 3. Late mortality was not related to DSWI. Of the remaining 44 patients, 35 (79.5%) filled-out the SF-36 correctly; 5 patients were not able to answer the questionnaire owing to language problems; 2 patients suffering from postoperative neurologic sequel could not reply; and 2 patients, 1 each from groups 1 and 3, refused to answer. As patients from groups 2 and 3 had both sternal excision and musculocutaneous flap, the SF-36 results were analyzed together and compared with the results obtained in patients from group 1 treated with vacuum-assisted closure. Patients from groups 2 and 3 scored significantly lower in the aspects of physical function, general health and vitality, than patients from group 1 (p < 0.05). Restrictions in comparison with an age- and sex-matched standard population (scores between 85 and 115) were found in 6 of 8 aspects in groups 2 and 3 and in 3 of 8 aspects in group 1 (Fig 1).
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Fig 1. Age and sex-matched comparison of the aspects assessed with the Short Form-36 (SF-36) for group 1 patients (sternal refixation; light gray bars) compared with patients from groups 2 and 3 (sternal resection and musculocutaneous flap; dark gray bars). Normal value for an age- and sex-matched standard population is 100 (range, 85 to 115). (BP = bodily pain; GH = general health; MH = mental health; ns = not significant; PF = physical functioning; RE = emotional role functioning; RP = physical role functioning; SF = social functioning; VT = vitality.)
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The analysis of the data obtained with the additional questionnaire revealed that respiratory problems are not that important and that, despite the long medical treatment, patient satisfaction comes up to 8.2 in group 1, 6.4 in group 2, and 6.7 in group 3 (scale from 0 = not satisfied at all, to 10 = very satisfied). However, patients from groups 2 and 3 were disappointed by the cosmetic result, with an average value of 5.0 in group 2, 2.7 in group 3, and 7.8 in group 1. Despite the good results, translated through the SF-36 under the aspect bodily pain, patients from group 1 had an average value of 2.8, compared with 4.2 in group 2 and 1.6 in group 3, looking at the aspect sternal pain (scale from 0 = no pain, to 10 = very painful).
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Comment
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According to the literature, the incidence of DSWI varies between 1% and 3% [1–7]. Our findings correlate with those of a recent study using the El Oakley classification [17]. The incidence of DSWI (El Oakley class 2B) was 1.1%. The bacteriologic spectrum is also similar to other studies with a majority of S aureus infection (41.8%) and coagulase negative Staphylococcus (32.7%) identified in bacteriologic cultures [18]. Blood cultures were positive in 16 patients (29.1%) and were not predictive for the success rate of the treatment modality. There was also no significant difference in terms of outcome based on organism in the present study, which is consistent with the findings from Douville and colleagues [18]. In their study, vacuum-assisted treatment was not available, and patients underwent débridement, drainage, and sternal wire reclosure or muscle flap. Overall mortality in this collective was 12.6%, but 6.3% was sternal related, which is slightly higher than the observed overall mortality of 5.4% in our collective, of which 3.6% was sternal related [18].
Our results confirm partly some findings described in earlier studies: COPD, diabetes mellitus, obesity, the use of bilateral internal thoracic artery, as well as a prolonged postoperative recovery and the use of intra-aortic balloon pump are associated with a higher incidence of sternal dehiscence and wound infection [5–7].
Sternal preservation should be the principal goal in these patients. However, a recent study reported that sternal preservation in patients with El Oakley class 2 B infection failed in 6 of 32 patients (18.8%). Sternal refixation was successful in 41.9%, which is quite similar to our findings [18]. When more of one of the described risk factors for DSWI is present, especially the use of bilateral internal thoracic artery and a poor vascularized, multifractured sternum, sternal resection and musculocutaneous flap to control DSWI in these old and sick patients will be more often necessary. This treatment provides excellent infection control and allows reduction of mortality and morbidity in that high-risk collective. Death during the follow-up in patients from groups 2 and 3 is considerable, reflecting the comorbidities in this collective. However, 2 years after surgery, more than 80% of the patients are still alive, and deaths were not related to DSWI.
In comparison with a standard age- and sex-matched population, patients from groups 2 and 3 showed a significant limitation in QoL in 6 of 8 aspects, which is probably mainly related to the general health condition and not only related to the sternal wound healing problems. Our study confirms that both treatment modalities provide very efficient pain control, and sternal resection and musculocutaneous flap does not induce serious respiratory problems in the follow-up, as already described [14]. However, many patients are disappointed by the cosmetic result of sternal resection and musculocutaneous flap. A secondary resection of the skin, covering the musculocutaneous flap is feasible and may improve the cosmetic result.
We are aware that the small number of patients is a limitation of the present study, explaining that multivariate logistic regression analysis—limited to three aspects (as the number of factors should not exceed the number of units divided by 10)—revealed no statistical significant differences looking at the characteristics in patients from group 1 and 2. However, univariate analysis confirmed that the risk factors favoring DSWI can also be found in patients from group 2, in whom refixation of the sternum failed, despite the use of vacuum-assisted closure.
Preservation of the sternum and sternal refixation seems to be a successful procedure for younger patients, for those with a good quality of the sternum, and for those without cumulation of the above mentioned risk factors. Reoperations were significantly more frequent in patients from group 1 compared with those from group 3. Nevertheless, average length of stay was significantly shorter for patients with successful sternal refixation. Comparing the technique of closure between patients from group 1 (successful sternal closure) and group 2 (sternal refixation failed), one may assume that partial resection and refixation of the sternum by the modified Robicsek technique [19, 20] provides the best results. Follow-up of patients from group 1 is uneventful, with a low mortality rate and a QoL similar to the recently reported QoL observed in patients undergoing on-pump coronary artery bypass surgery [21]. We believe that vacuum-assisted treatment, in case of DSWI improves and accelerates the cleaning and débridement of the infected wound, without compromising secondary sternal closure in a safe and optimal condition.
We conclude that preservation of the sternum should be the principal aim of surgical treatment in patients with DSWI. Early diagnosis, débridement, and the use of the vacuum-assisted system followed by secondary sternal closure, with liberal use of the Robicsek technique, allows good long-term results. Quality of life is nearly normal in these patients, and there is no major sternal pain. Resection and musculocutaneous flap is a surgical procedure, which should be reserved for high-risk patients. This approach provides a safe and definitive control of the infection and offers acceptable results in term of pain control and QoL.
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Abstract
Introduction
