**7. Morbidity and mortality**

288 Special Topics in Cardiac Surgery

Several risk analyses are available to estimate the individual patient's propensity for developing DSWI. For example, using Society of Thoracic Surgery National Cardiac Database information, Fowler et al created a model to estimate the risk for systemic infection after coronary artery bypass surgery using patient characteristics available preoperatively [13]. The Fowler model also provides for inclusion of important intraoperative details known to influence postoperative infection including the need for intra-aortic balloon counterpulsation and prolonged cardiopulmonary bypass times [13]. Although the model devised by Fowler et al was based on various cases of major infection after coronary artery surgery, including DSWI, the authors did validate the model as predictive of infection in a test population from the STS Database, and the model was also recently validated in a different cohort of patients from the UK as being predictive of DSWI [38]. The EuroSCORE system also has been shown to predict infection and associated mortality with acceptable

Despite advancements in most aspects of perioperative care, rates of sternal wound complications, including mediastinitis, following adult cardiac surgery have varied little over the past 30 years [2-6], although incremental reduction in single center rates of DSWI have been noted and attributed to adjunctive measures such as strict perioperative glucose control [40]. As noted previously, rates of DSWI vary with regard to the specific definition used to describe the pathology encountered and the patient population studied. In general, reported rates of DSWI are relatively low, ranging from 0.25% to 3.6 % [2-9, 38, 39, 41, 42]. However, the incidence of superficial sternal infection excedes that of deep sternal infection by as many as three times [10, 41, 43], and Francel has stated that as many as 70% of patients

Depending on the virulent nature of the sternal wound infection, patients typically present within 30 days of cardiac surgery. The most common symptoms include sternal wound drainage, sternal instability, fever, and malaise. In many cases, a high index of suspicion is required to establish the diagnosis, especially when classic signs and symptoms are absent. In addition, it is often difficult to distinguish on physical examination the difference between deep sternal wound infection (infection present beneath the sternum) and superficial sternal infection. Therefore, early wound opening and inspection with appropriate sampling of tissue for bacteriologic assessment is strongly encouraged when

One of the most reliable signs of DSWI is sternal instability, which frequently implies a deeper problem than can be appreciated at the superficial level [44]. While sternal instability can be tested on physical examination, we have often noted that the patient themselves will typically report sternal clicking with inspiration, cough, or various other physical maneuvers, so this information should be thoughtfully considered if DSWI diagnosis is

The use of various radiographic examinations is often encouraged when evaluating for DSWI, and, in fact, is included as part of the CDC guidelines for defining mediastinitis [25]. Formerly, PA and lateral chest radiograph was the investigative procedure of choice, where details such

with poststernotomy infection will have superficial tissue involvement [44].

discrimination [39].

**5. Incidence** 

**6. Diagnosis** 

being entertained.

sufficient clinical suspicion exists.

Mediastinal infection negatively impacts early, mid-term, and long-term survival after adult heart surgery [2, 7-12]. While it is intuitive that clinically serious DSWI reduces 30-day and/or in-hospital survival relative to similar patients not suffering this complications, the effect of DSWI on long-term survival is especially insulting since many patients referred for heart surgery expect to gain a survival advantage compared with other treatment options for their underlying heart disease [49].

Prior to the development of modern protocols for DSWI management, which include thorough sternal debridement and use of vascularized flaps to repair the mediastinal defect resulting from debridement, early mortality from DSWI exceeded 50% [50]. In the "modern era," reported rates of in-hospital or 30-day DSWI mortality for range from 7% to over 30% [11,14, 35, 42, 51, 52]. In our own recent experience, early mortality for DSWI is approximately 16% [14]. Therefore, despite many advancements in intensive care medicine, DSWI continues to be a deadly complication. Death in the early period is typicaly the result of sepsis or other infectious complications including multiorgan failure [12]. Morisaki et al. recently demonstrated methicillin-resistent *S. aureus* infection to be an independent risk factor for in-hospital mortality in their cohort of poststernotomy DSWI patients [53].

Patients surviving infectious complications and the acute insult of DSWI exhibit reduced mid-term survival compared with controls. For example, one-year mortality for DSWI following CABG is significantly increased compared with similar patients who did not develop DSWI [2, 8, 10]. Milano et al and Braxton et al both demonstrated a doubling of mid-term mortality among patients with DSWI after CABG compared with controls [9, 54]. Karra et al examined predictors of one-year mortality after treatment for DSWI and found that delay in closing the mediastinal defect; age over 65 years; need for ICU care prior to sternal debridement; and methicillin-resistent *S. aureus* infections were each independently associated with mortality [7].

Long-term survival has consistently been demonstrated to suffer in patients with a history of poststernotomy DSWI [5, 8, 9, 12, 35, 52, 54-56, Figure 1]. For example, Filsoufi et al reviewed nearly 5,800 adult heart surgery patients at a single institution over 8 years and found DSWI to be associated with significantly reduced 5-year survival compared with patients who did not develop DSWI [35]. Similarly, Risnes et al reviewed their experience of over 18,000 cardiac surgical patients with a mean follow-up of over 10 years. Long-term survival for patients whose course was complicated by DSWI was <50% compared with >70% for patients without DSWI, and DSWI was independently associated with reduced long-term survival after cardiac surgery [HR 1.59; 95% CI 1.16 – 2.70, p = 0.003] [12]. Similar data have been also been reported by Toumpoulis et al. [55].

Sternal Wound Complications Following Cardiac Surgery 291

[58]. In our own recently described experience, methicillin-sensitive and methicillin-resistent *S. aureus* each accounted for 35% of wound isolates, while CNS was present in 12%, and gram negative organisms were found in 18% [14]. It is noteworthy that our protocols for preoperative preparation of the cardiac surgical patient do not routinely incorporate mupirocin treatment. Additionally, many patients included in our cohort of patients treated for DSWI underwent primary cardiac surgery at referring facilities. Therefore, specific details in these patients predisposing to a certain pathogen were often lacking. Risk factors for the development of methicillin-resistent *S. aureus* poststernotomy mediastinitis include previous hospitalization and takeback for bleeding after the original cardiac surgical procedure [59]. Gardlund et al have attributed the development of *S. aureus* infection to the development of bacteremia [60], which is corroborated by our own data in which 50% of patients treated for DSWI had evidence of bacteremia or septicemia (Jones classification 3b) at the time of clinical presentation with DSWI [14]. Finally, it has been demonstrated that methicillin-resistent strains of *S. aureus* are more virulent and deadly than methicillinsensitive strains, and, in fact, methicillin resistance was the only independent predictor of

In contrast, *S. epidermidis* often presents with a rather indolent course, often not manifesting clinically until 3 weeks or more postoperatively [62]. CNS is frequently isolated in cases of sternal instability or nonunion, which may itself arise from obesity or acute or chronic pulmonary disease [60]. CNS has recently been noted to of increasing incidence and has been reported to be present in roughly 50% of sternal infections in some series [6, 11, 60]. Gram negative organisms contribute less commonly to the pathogenesis of DSWI. Gramnegative infections of the mediastinum classically arise in the setting of other postoperative infectious complications such pneumonia, urinary tract infections, intra-abdominal infections, or other nosocomial infections [58, 60]. Mekontso-Dessap et al reviewed their experience with DSWI after cardiac surgery and found that Enterococcus species were the most common isolates in early cases of DSWI (<14 days), which likely arise from translocation of these bacteria from other sources in the host [63]. In contrast, *Staphylococcus*  species, often CNS, were the most common isolates in cases presenting more remotely from

One of the most impactful consequences of DSWI is the costs incurred in its management, in part due to the multiple associated conditions that frequently complicate the clinical picture of these sick patients [4, 12]. The average hospital costs for patients treated for DSWI is approximately 2.5 to 3 times that of similarly matched patients who enjoy an uncomplicated postoperative course [23, 64, 65]. As noted, increased costs are primarily attributed to associated comorbid conditions that arise during the treatment of mediastinitis, increased length of hospital stays, including frequent need for ICU services, and the need for multiple surgical procedures when using traditional approaches to DSWI [4, 23]. For example, Hollenbeak et al found that patients with DSWI remained hospitalized an average of 3 weeks longer than noninfected patients after coronary artery surgery [2]. Interestingly, in the same study it was noted that DSWI patients who ultimately expired incurred nearly \$61,000 US dollars more in costs than other DSWI patients who ultimately survived, presumably secondary to the multiple comorbidities associated with clinically aggressive mediastinitis [2]. Using more recently acquired information, Speir et al found that mediastinitis was the single

early mortality in one analysis [61].

the original surgery [63].

**9. Cost of DSWI** 

Fig. 1. From Braxton et al with permission [8], patients suffering mediastinal infection after coronary artery bypass grafting have worse overall long-term survival compared with similar patients not experiencing the complication.

It is unclear as to the specific reasons for worse long-term survival after DSWI is successfully treated, but cardiac-related deaths or progression of cardiovascular disease appears to be a common cause of death for those with DSWI [8, 12]. In addition, Chu et al recently reported that patients with peripheral vascular disease had worse outcomes long-term after coronary artery surgery [57]. We recently evaluated long-term survival in a cohort of 222 adult cardiac surgical patients treated at Duke University Hospital for poststernotomy mediastinitis. Using multivariable regression analysis and at a mean follow-up of 5.5 years, the following variables were noted to be independently associated with survival: heart failure [Hazard ratio (HR) 1.58, p = 0.029]; sepsis [HR 2.38, p <0.001]; peripheral vascular disease [HR 2.06, p = 0.001], age > 65 years [HR 1.61, p = 0.037]; and take back for bleeding [HR 2.96; p = 0.007] (unpublished data).

Not only does DSWI lead to increased mortality among post-surgical patients, it is also closely associated with other types of postoperative complications. For example, in a recent review of morbidity following coronary surgery from the Virginia Cardiac Surgery Quality Initiative, DSWI was the not only the most expensive complication, but it was also associated with a longer length of hospital stay, by more than two full weeks, than any other single postoperative complication, including perioperative stroke and renal failure [4]. Other reports have corroborated the impact of DSWI on overall hospital length of stay [2, 6, 52]. Speir et al also demonstrated that DSWI was the most likely form of postoperative morbidity to be associated with other complications such as prolonged ventilation, bleeding, renal failure, and atrial fibrillation [4]. DSWI has also been associated with increased rates of stroke, need for inotropic or mechanical cardiac support, and perioperative myocardial infarction, renal failure, and prolonged mechanical ventilation [12, 51].

### **8. Microbiology**

Numerous bacterial pathogens may contribute to DSWI, but the most commonly isolated organisms are *Staphylococcus*, either coagulase-negative *Staphylococcus (*CNS) or *S. aureus* 

Fig. 1. From Braxton et al with permission [8], patients suffering mediastinal infection after coronary artery bypass grafting have worse overall long-term survival compared with

It is unclear as to the specific reasons for worse long-term survival after DSWI is successfully treated, but cardiac-related deaths or progression of cardiovascular disease appears to be a common cause of death for those with DSWI [8, 12]. In addition, Chu et al recently reported that patients with peripheral vascular disease had worse outcomes long-term after coronary artery surgery [57]. We recently evaluated long-term survival in a cohort of 222 adult cardiac surgical patients treated at Duke University Hospital for poststernotomy mediastinitis. Using multivariable regression analysis and at a mean follow-up of 5.5 years, the following variables were noted to be independently associated with survival: heart failure [Hazard ratio (HR) 1.58, p = 0.029]; sepsis [HR 2.38, p <0.001]; peripheral vascular disease [HR 2.06, p = 0.001], age > 65 years [HR 1.61, p = 0.037]; and take back for bleeding

Not only does DSWI lead to increased mortality among post-surgical patients, it is also closely associated with other types of postoperative complications. For example, in a recent review of morbidity following coronary surgery from the Virginia Cardiac Surgery Quality Initiative, DSWI was the not only the most expensive complication, but it was also associated with a longer length of hospital stay, by more than two full weeks, than any other single postoperative complication, including perioperative stroke and renal failure [4]. Other reports have corroborated the impact of DSWI on overall hospital length of stay [2, 6, 52]. Speir et al also demonstrated that DSWI was the most likely form of postoperative morbidity to be associated with other complications such as prolonged ventilation, bleeding, renal failure, and atrial fibrillation [4]. DSWI has also been associated with increased rates of stroke, need for inotropic or mechanical cardiac support, and perioperative myocardial

Numerous bacterial pathogens may contribute to DSWI, but the most commonly isolated organisms are *Staphylococcus*, either coagulase-negative *Staphylococcus (*CNS) or *S. aureus* 

infarction, renal failure, and prolonged mechanical ventilation [12, 51].

similar patients not experiencing the complication.

[HR 2.96; p = 0.007] (unpublished data).

**8. Microbiology** 

[58]. In our own recently described experience, methicillin-sensitive and methicillin-resistent *S. aureus* each accounted for 35% of wound isolates, while CNS was present in 12%, and gram negative organisms were found in 18% [14]. It is noteworthy that our protocols for preoperative preparation of the cardiac surgical patient do not routinely incorporate mupirocin treatment. Additionally, many patients included in our cohort of patients treated for DSWI underwent primary cardiac surgery at referring facilities. Therefore, specific details in these patients predisposing to a certain pathogen were often lacking. Risk factors for the development of methicillin-resistent *S. aureus* poststernotomy mediastinitis include previous hospitalization and takeback for bleeding after the original cardiac surgical procedure [59]. Gardlund et al have attributed the development of *S. aureus* infection to the development of bacteremia [60], which is corroborated by our own data in which 50% of patients treated for DSWI had evidence of bacteremia or septicemia (Jones classification 3b) at the time of clinical presentation with DSWI [14]. Finally, it has been demonstrated that methicillin-resistent strains of *S. aureus* are more virulent and deadly than methicillinsensitive strains, and, in fact, methicillin resistance was the only independent predictor of early mortality in one analysis [61].

In contrast, *S. epidermidis* often presents with a rather indolent course, often not manifesting clinically until 3 weeks or more postoperatively [62]. CNS is frequently isolated in cases of sternal instability or nonunion, which may itself arise from obesity or acute or chronic pulmonary disease [60]. CNS has recently been noted to of increasing incidence and has been reported to be present in roughly 50% of sternal infections in some series [6, 11, 60].

Gram negative organisms contribute less commonly to the pathogenesis of DSWI. Gramnegative infections of the mediastinum classically arise in the setting of other postoperative infectious complications such pneumonia, urinary tract infections, intra-abdominal infections, or other nosocomial infections [58, 60]. Mekontso-Dessap et al reviewed their experience with DSWI after cardiac surgery and found that Enterococcus species were the most common isolates in early cases of DSWI (<14 days), which likely arise from translocation of these bacteria from other sources in the host [63]. In contrast, *Staphylococcus*  species, often CNS, were the most common isolates in cases presenting more remotely from the original surgery [63].

### **9. Cost of DSWI**

One of the most impactful consequences of DSWI is the costs incurred in its management, in part due to the multiple associated conditions that frequently complicate the clinical picture of these sick patients [4, 12]. The average hospital costs for patients treated for DSWI is approximately 2.5 to 3 times that of similarly matched patients who enjoy an uncomplicated postoperative course [23, 64, 65]. As noted, increased costs are primarily attributed to associated comorbid conditions that arise during the treatment of mediastinitis, increased length of hospital stays, including frequent need for ICU services, and the need for multiple surgical procedures when using traditional approaches to DSWI [4, 23]. For example, Hollenbeak et al found that patients with DSWI remained hospitalized an average of 3 weeks longer than noninfected patients after coronary artery surgery [2]. Interestingly, in the same study it was noted that DSWI patients who ultimately expired incurred nearly \$61,000 US dollars more in costs than other DSWI patients who ultimately survived, presumably secondary to the multiple comorbidities associated with clinically aggressive mediastinitis [2]. Using more recently acquired information, Speir et al found that mediastinitis was the single

Sternal Wound Complications Following Cardiac Surgery 293

Fig. 2. Preparation of the omental flap graft for transfer to the mediastinum from Milano et

al with permission [80]. After preparation of the mediastinum [A], a laparotomy is performed and the greater omental graft is prepared by mobilizing it from the transverse colon [B]. Once the graft is tunneled through an anterior diaphragm incision, it is secured in the mediastinum to fill the defect. Care is taken to avoid twisting or kinking the omental graft as it is delivered from the abdomen into the mediastinum [C]. The mediastinum is then

closed over drains with retention sutures. The drains are placed to bulb suction [D].

procedures and has been utilized successfully [77].

omental pedicle using a laparoscopic approach may have advantages over open abdominal

Jurkiewicz et al first reported on the successful use of muscle flaps in DSWI in 1980 [78], while the Emory groups' experience with muscle flap repair of the infected mediastinum refined approaches and clarified advantages of these techniques [26]. As with omental flap repair, discrete advantages of complete mediastinal repair with vascularized muscle flaps were demonstrated as compared with closed chest irrigation [26, 79]. Milano et al compared omental and pectoralis muscle flap repairs for the infected mediastinum and found that procedural details, early complications, and hospital length of stay were all improved with omental flap repair [80]. Omental flap repair also trended towards improved survival and reduced chronic pain when compared with pectoralis flap procedures [80]. In fact, significant long-term complications can be associated with muscle flap repair of the mediastinum including paresthesias, sternal instability, truncal weakness, and prolonged pain syndromes [9, 26, 81, 82]. Reporting on the long term results of muscle flap coverage of the mediastinum, Ringelman noted persistent pain in over 50% of patients, numbness and paresthesias in 44%, sternal instability in over 40%, and shoulder weakness in 1/3 of patients [82]. It is worth noting, however, that unfavorable outcomes with open packing and/or mediastinal irrigation prompted recommendations for aggressive mediastinal debridement including radical sternectomy

most costly complication in Virginia after coronary artery surgery, raising the cost of care by over \$62,000 US dollars, or more than 240% increase, on average, [4].

Therefore, it is apparent that treatment of these critically ill patients is extremely expensive to the hospital system, even if the complication is uncommonly encountered. As a result, and based on increased scrutiny of various hospital-associated conditions, the US Center for Medicare and Medicaid Services no longer reimburses for hospital costs incurred in treatment of DSWI following coronary artery bypass surgery [66]. Interestingly, however, it appears that use of negative pressure therapy in the treatment of DSWI contains associated costs. For example, Mokhtari et al reported the use of VAC therapy to be cost effective and efficacious in eradicating mediastinal infection [65]. In our own experience, patients treated with negative pressure therapy for DSWI had costs that were \$150,000 US dollars less than the average Medicare charges for treatment required for DSWI (\$152,00 vs. \$ 300,000) [67].

### **10. Treatment of DSWI**

Upon establishing the diagnosis of sternal wound infection, the immediate goal of treatment is complete eradication of infection followed by stabilization of the sternum and chest wall. Multiple strategies for managing mediastinitis have been proposed and range from open mediastinal packing to debridement with closure over drains, to placement of vascularized tissue flaps. In addition, negative pressure therapy (NPT) has been used to aide in the treatment of mediastinal infection, as first reported in 1999 [68]. Several initial series described the use of NPT for treating mediastinitis and outlined potential benefits of this approach to controlling mediastinal infection [15, 16, 45, 69, 70]. However, a consensus as to best treatment for mediastinal infection has yet to be established. For example, Schimmer et al recently surveyed 79 cardiac surgery programs in Germany to query DSWI management strategies [71]. They found that approximately 1/3 of the centers preferentially used NPT for controlling mediastinal contamination, while another 1/3 use closed chest irrigation, and another 1/3 combine management approaches [71]. Other groups continue to advocate more aggressive surgical therapy in addressing infected sternal wounds [7, 72].

Initially, the primary treatment for DSWI was open packing followed by secondary closure [73]. This method was labor intensive, cumbersome, and was characterized by significant rates of recurrent infection and other complications [58]. Shortly thereafter, Schumaker and Mandelbaum proposed early closure over drains [74], which allowed continual irrigation of the infected mediastinum [73, 74]. Although this approach represented an improvement relative to open packing procedure, the latter procedure was still associated with failure rates of at least 25% [73].

Omental flap repair of the infected mediastinum was originally reported in 1976 by Lee [75] and has been shown to have distinct advantages over continuous antiobiotic irrigation through drains [76] and over muscle flaps for sternal wound defect repair [9, 14]. This is thought to occur by obliterating dead space, a mechanism that can also be credited to muscle flap repair of the open mediastinum [26]. However, the omentum may have angiogenic and immunologic properties that stimulate more complete sternal defect healing [58]. Other advantages of using the greater omentum to flap the sternal defect include superior malleability and excellent blood flow. As originally described, traditional omental flap repair of the mediastinum involves a laparotomy to mobilize and place the graft through the anterior portion of the diaphragm [Figure 2]. More recently, harvesting the

most costly complication in Virginia after coronary artery surgery, raising the cost of care by

Therefore, it is apparent that treatment of these critically ill patients is extremely expensive to the hospital system, even if the complication is uncommonly encountered. As a result, and based on increased scrutiny of various hospital-associated conditions, the US Center for Medicare and Medicaid Services no longer reimburses for hospital costs incurred in treatment of DSWI following coronary artery bypass surgery [66]. Interestingly, however, it appears that use of negative pressure therapy in the treatment of DSWI contains associated costs. For example, Mokhtari et al reported the use of VAC therapy to be cost effective and efficacious in eradicating mediastinal infection [65]. In our own experience, patients treated with negative pressure therapy for DSWI had costs that were \$150,000 US dollars less than the average Medicare charges for treatment required

Upon establishing the diagnosis of sternal wound infection, the immediate goal of treatment is complete eradication of infection followed by stabilization of the sternum and chest wall. Multiple strategies for managing mediastinitis have been proposed and range from open mediastinal packing to debridement with closure over drains, to placement of vascularized tissue flaps. In addition, negative pressure therapy (NPT) has been used to aide in the treatment of mediastinal infection, as first reported in 1999 [68]. Several initial series described the use of NPT for treating mediastinitis and outlined potential benefits of this approach to controlling mediastinal infection [15, 16, 45, 69, 70]. However, a consensus as to best treatment for mediastinal infection has yet to be established. For example, Schimmer et al recently surveyed 79 cardiac surgery programs in Germany to query DSWI management strategies [71]. They found that approximately 1/3 of the centers preferentially used NPT for controlling mediastinal contamination, while another 1/3 use closed chest irrigation, and another 1/3 combine management approaches [71]. Other groups continue to advocate

more aggressive surgical therapy in addressing infected sternal wounds [7, 72].

Initially, the primary treatment for DSWI was open packing followed by secondary closure [73]. This method was labor intensive, cumbersome, and was characterized by significant rates of recurrent infection and other complications [58]. Shortly thereafter, Schumaker and Mandelbaum proposed early closure over drains [74], which allowed continual irrigation of the infected mediastinum [73, 74]. Although this approach represented an improvement relative to open packing procedure, the latter procedure was still associated with failure

Omental flap repair of the infected mediastinum was originally reported in 1976 by Lee [75] and has been shown to have distinct advantages over continuous antiobiotic irrigation through drains [76] and over muscle flaps for sternal wound defect repair [9, 14]. This is thought to occur by obliterating dead space, a mechanism that can also be credited to muscle flap repair of the open mediastinum [26]. However, the omentum may have angiogenic and immunologic properties that stimulate more complete sternal defect healing [58]. Other advantages of using the greater omentum to flap the sternal defect include superior malleability and excellent blood flow. As originally described, traditional omental flap repair of the mediastinum involves a laparotomy to mobilize and place the graft through the anterior portion of the diaphragm [Figure 2]. More recently, harvesting the

over \$62,000 US dollars, or more than 240% increase, on average, [4].

for DSWI (\$152,00 vs. \$ 300,000) [67].

**10. Treatment of DSWI** 

rates of at least 25% [73].

Fig. 2. Preparation of the omental flap graft for transfer to the mediastinum from Milano et al with permission [80]. After preparation of the mediastinum [A], a laparotomy is performed and the greater omental graft is prepared by mobilizing it from the transverse colon [B]. Once the graft is tunneled through an anterior diaphragm incision, it is secured in the mediastinum to fill the defect. Care is taken to avoid twisting or kinking the omental graft as it is delivered from the abdomen into the mediastinum [C]. The mediastinum is then closed over drains with retention sutures. The drains are placed to bulb suction [D].

omental pedicle using a laparoscopic approach may have advantages over open abdominal procedures and has been utilized successfully [77].

Jurkiewicz et al first reported on the successful use of muscle flaps in DSWI in 1980 [78], while the Emory groups' experience with muscle flap repair of the infected mediastinum refined approaches and clarified advantages of these techniques [26]. As with omental flap repair, discrete advantages of complete mediastinal repair with vascularized muscle flaps were demonstrated as compared with closed chest irrigation [26, 79]. Milano et al compared omental and pectoralis muscle flap repairs for the infected mediastinum and found that procedural details, early complications, and hospital length of stay were all improved with omental flap repair [80]. Omental flap repair also trended towards improved survival and reduced chronic pain when compared with pectoralis flap procedures [80]. In fact, significant long-term complications can be associated with muscle flap repair of the mediastinum including paresthesias, sternal instability, truncal weakness, and prolonged pain syndromes [9, 26, 81, 82]. Reporting on the long term results of muscle flap coverage of the mediastinum, Ringelman noted persistent pain in over 50% of patients, numbness and paresthesias in 44%, sternal instability in over 40%, and shoulder weakness in 1/3 of patients [82]. It is worth noting, however, that unfavorable outcomes with open packing and/or mediastinal irrigation prompted recommendations for aggressive mediastinal debridement including radical sternectomy

Sternal Wound Complications Following Cardiac Surgery 295

Fig. 3. Actuarial (panel A) and adjusted (panel B) survival curves for patients with

permission.

poststernotomy mediastinitis treated with vacuum-assisted closure (VAC) as compared to control subjects who did not experience mediastinitis after heart surgery. No difference in long-term survival was demonstrated between the groups. From Sjogren et al [93], with

Another study from the UK demonstrated that midterm survival for patients with postoperative mediastinitis was similar to patients not suffering the complication [51]. Similar results have been reported by Cayci et al from Columbia University, who found that DSWI was associated with increased early mortality but long-term survival was not different from controls. Furthermore, DSWI was not an independent predictor of mortality in their single-center experience [52]. It is unclear as to why this may be the case, but it is notable that NPT was used in over 80% of patients with mediastinitis as a

[78, 83]. While effective in removing devitalized and infected tissue, the resulting sternal defect required large-volume vascularized tissue such as muscle flaps or large omental flaps to obliterate deadspace. As a result, many of the negative long-term consequences often experienced and attributed to muscle flap repair may actually have originated with radical sternal debridement. After the introduction of NPT management of mediastinal sepsis/infection, radical sternal debridement has been de-emphasized [14, 16, 83, 84]. Stated differently, the use of NPT to treat the infected mediastinum helps to avoid radical sternal debridement and likely avoids chronic syndromes previously seen and perhaps erroneously attributed to treatment methods.

Obdeijn et al introduced the use of negative pressure therapy (NPT) for treatment of the infected mediastinum after median sternotomy [68]. The introduction of vacuum-assisted closure (VAC®) technology [Kinetic Concepts Inc. USA San Antonio, TX], based on the application of negative or subatmospheric pressure to the wound, has improved management of DSWI, as demonstrated by several groups including our own, and is now considered a cornerstone in the management of these complex clinical scenarios [14, 15, 70, 73]. Negative pressure therapy appears to induce effective proliferation of the effectors of wound healing [85] removes wound exudates, improves regional blood flow [86], and reduces accumulation of inflammatory mediators such that earlier and more complete wound healing results [70]. Laboratory studies also show that NPT induces early wound healing through microdeformations within the wound, stimulating cell division, proliferation, and angiogenesis [73, 87]. One distinct advantage of the mechanisms of NPT is more thorough eradication of infection, stimulation of vigorous wound granulation, and the subsequent promotion of safe and effective sternal closure either primarily or with rigid osteosynthesis [11, 14, 88]. Wound treatment with NPT appears to be significantly lower rates of recurrent wound complications such as reinfection, seromas, or hematomas [14, 89, 90]. However, there is a recognized tendency for recurrent infection when MRSA is the inciting organism or with prolonged mechanical ventilation [91].

Clinically, NPT has been associated with significantly lower mortality rates in the acute management of mediastinitis [11, 89]. For instance, Petzina et al recently compared 118 patients with poststernotomy DSWI and demonstrated that patients treated with NPT had better survival and less sternal re-infection compared with patients in whom NPT was not used [89]. In addition, as may have been expected, shorter hospital stays were noted within the NPT group. Baillot et al reported similar results by, while documenting a reduction in acute DSWI mortality from 14.1% to less than 5% when NPT was incorporated into treatment regimens [11]. Finally, De Feo et al evaluated 157 patients with poststernotomy DSWI at a single institution over 15 years. Patients in whom NPT was incorporated in the treatment regimen had reduced early mortality rates and, reduced reinfection rates, and slightly reduced overall hospital stays [92].

As noted previously, long term mortality among patients with DSWI has been historically poor compared with similar patients not suffering the complication, but recent evidence suggests this may be changing. The first evidence for this phenomenon was reported by Sjogren et al, who compared 46 patients with poststernotomy mediastinitis managed with NPT with a matched cohort of cardiac surgical patients not experiencing postoperative mediastinitis [93]. Actuarial and adjusted 5-year survival was not different between groups, demonstrating for the first time that long-term results of heart surgery were not negatively impacted by DSWI [Figure 3].

[78, 83]. While effective in removing devitalized and infected tissue, the resulting sternal defect required large-volume vascularized tissue such as muscle flaps or large omental flaps to obliterate deadspace. As a result, many of the negative long-term consequences often experienced and attributed to muscle flap repair may actually have originated with radical sternal debridement. After the introduction of NPT management of mediastinal sepsis/infection, radical sternal debridement has been de-emphasized [14, 16, 83, 84]. Stated differently, the use of NPT to treat the infected mediastinum helps to avoid radical sternal debridement and likely avoids chronic syndromes previously seen and perhaps

Obdeijn et al introduced the use of negative pressure therapy (NPT) for treatment of the infected mediastinum after median sternotomy [68]. The introduction of vacuum-assisted closure (VAC®) technology [Kinetic Concepts Inc. USA San Antonio, TX], based on the application of negative or subatmospheric pressure to the wound, has improved management of DSWI, as demonstrated by several groups including our own, and is now considered a cornerstone in the management of these complex clinical scenarios [14, 15, 70, 73]. Negative pressure therapy appears to induce effective proliferation of the effectors of wound healing [85] removes wound exudates, improves regional blood flow [86], and reduces accumulation of inflammatory mediators such that earlier and more complete wound healing results [70]. Laboratory studies also show that NPT induces early wound healing through microdeformations within the wound, stimulating cell division, proliferation, and angiogenesis [73, 87]. One distinct advantage of the mechanisms of NPT is more thorough eradication of infection, stimulation of vigorous wound granulation, and the subsequent promotion of safe and effective sternal closure either primarily or with rigid osteosynthesis [11, 14, 88]. Wound treatment with NPT appears to be significantly lower rates of recurrent wound complications such as reinfection, seromas, or hematomas [14, 89, 90]. However, there is a recognized tendency for recurrent infection when MRSA is the

Clinically, NPT has been associated with significantly lower mortality rates in the acute management of mediastinitis [11, 89]. For instance, Petzina et al recently compared 118 patients with poststernotomy DSWI and demonstrated that patients treated with NPT had better survival and less sternal re-infection compared with patients in whom NPT was not used [89]. In addition, as may have been expected, shorter hospital stays were noted within the NPT group. Baillot et al reported similar results by, while documenting a reduction in acute DSWI mortality from 14.1% to less than 5% when NPT was incorporated into treatment regimens [11]. Finally, De Feo et al evaluated 157 patients with poststernotomy DSWI at a single institution over 15 years. Patients in whom NPT was incorporated in the treatment regimen had reduced early mortality rates and, reduced reinfection rates, and

As noted previously, long term mortality among patients with DSWI has been historically poor compared with similar patients not suffering the complication, but recent evidence suggests this may be changing. The first evidence for this phenomenon was reported by Sjogren et al, who compared 46 patients with poststernotomy mediastinitis managed with NPT with a matched cohort of cardiac surgical patients not experiencing postoperative mediastinitis [93]. Actuarial and adjusted 5-year survival was not different between groups, demonstrating for the first time that long-term results of heart surgery were not negatively

erroneously attributed to treatment methods.

inciting organism or with prolonged mechanical ventilation [91].

slightly reduced overall hospital stays [92].

impacted by DSWI [Figure 3].

Fig. 3. Actuarial (panel A) and adjusted (panel B) survival curves for patients with poststernotomy mediastinitis treated with vacuum-assisted closure (VAC) as compared to control subjects who did not experience mediastinitis after heart surgery. No difference in long-term survival was demonstrated between the groups. From Sjogren et al [93], with permission.

Another study from the UK demonstrated that midterm survival for patients with postoperative mediastinitis was similar to patients not suffering the complication [51]. Similar results have been reported by Cayci et al from Columbia University, who found that DSWI was associated with increased early mortality but long-term survival was not different from controls. Furthermore, DSWI was not an independent predictor of mortality in their single-center experience [52]. It is unclear as to why this may be the case, but it is notable that NPT was used in over 80% of patients with mediastinitis as a

Sternal Wound Complications Following Cardiac Surgery 297

Fig. 5. Suggested algorithm for management of mediastinal infection after cardiac surgery via median sternotomy, with permission from Sjogren et al [15]. Emphasis is placed on gentle sternal debridement, negative pressure therapy to the mediastinum, and closure

As noted previously, successful treatment of DSWI begins with recognition of signs and symptoms of sternal infection, which may occasionally be subtle. Sternal wound exploration to ensure a prompt and accurate diagnosis is warranted when signs of mediastinitis are present. This approach also helps to distinguish between superficial and deep sternal infections. At the time of initial sternal exploration, tissues and fluid should be obtained for bacteriologic analysis. Targeted antibiotic therapy for 4-6 weeks duration is prescribed and is determined by the culture results [14, 15]. If the infectious process extends beneath the facial layer, all sternal hardware should be removed. The sternum itself is then gently debrided of grossly devitalized tissue, but wide excision of the sternum is not necessary and may be injurious and counterproductive. Limited sternal debridement is now preferred and good results have been seen with this approach [14, 16, 83, 93, 94]. Negative pressure therapy is then instituted on the opened incision after limited sternal debridement. The polyurethane foam is subsequently changed in the operating room or at the bedside every 2- 3 days. During this time, assessment as to the state of the sternum is made to determine if mediastinal flap repair is required or if secondary sternal closure is possible. Our general approach for determining when the sternum can reliably be reapproximated is based on the state of the sternum after several days of NPT. Wound characteristics precluding secondary

based on monitored serum C-reactive protein levels.

means for clearing infection, and nearly 50% of patients in their cohort were managed with vac therapy alone or vac + secondary sternal closure. In our own series, we found that use of NPT for controlling mediastinal infection was an independent predictor of survival on multivariable analysis [unpublished data], and that patients managed with NPT had significantly improved long term survival compared with patients not treated with NPT [Figure 4].

Fig. 4. Kaplan Meier survival curves for patients with poststernotomy mediastinitis treated with negative pressure therapy (NPT) or by traditional means for controlling mediastinal infection (controls). Patients treated with NPT had significantly improved long-term survival by log rank analysis.
