**4. Outcomes and cost of DSWI**

Unsurprisingly, DSWI negatively affected outcomes in cardiac surgery. Even with the adoption of modern treatment strategies, the reported in-hospital mortality for DSWI varies from 1.1 to 19% [6-9,11,16,45]. Although the mortality rate is similar to data reported from the 1980s, it appears that implementation of negative pressure wound therapy (NPWT) may improve long-term survival of patients [18,20,46]. Regardless of treatment strategy, in-hospital stay of DSWI patients is at least two weeks longer compared to patients with an uncomplicated post-operative course [6,10,11]. DSWI-related morbidity was repeatedly reported in relation to prolonged mechanical ventilation, renal impairment, atrial and ventricular arrhythmias, cerebrovascular accidents, need for hemodynamic support, and healing-related complications [20,47]. The cause of death in the early post-operative period is mostly multiple organ failure initiated by sepsis or specific DSWI-related complications such as serious bleeding [6-8,16,18, 20]. Predictors of a poor outcome in DSWI patients that have been reported include length of intensive care unit (ICU) stay, late indication for surgical revision, bacteremia, hemodynamic instability, and prolonged mechanical ventilation [47,48]. Loop et al presented the worse survival data of DSWI in patients operated on during the 1980s in comparison with a standard CABG population within a 3-year follow-up after surgery [6]. Survival analyses published in the last decade consistently confirm long-term complications of patients with mid-, and long term survival rates who were successfully treated for DSWI (Table 3) [8,11,12,14,15,18,22,46]. Specific reasons for worsening of long-term survival are not yet clear. Risnes et al reported significantly higher cardiac-related deaths in the post-DSWI group (34.6 vs. 21.4%, p<0.006) and poorer survival for males ten years after surgery [15]. In contrast with this data, Sjoegren et al and Bailot et al showed unimpaired long-term survival of DSWI patients in comparison with patients who had uncomplicated surgery once NPWT was used [18,46].

**3. Microbiology of DSWI and routes of infection**

496 Artery Bypass

independent risk factor for overall mortality [44].

**4. Outcomes and cost of DSWI**

Staphylococci, either S. aureus (SA) or coagulase-negative Staphylococcus (CONS) represent the most causative organism of DSWI, accounting for 60 to 80% of cases [34]. The proportion of individual strains of Staphylococcus and their methicillin-sensitivity varies between countries and institutions, reflecting their long-term hygienic and antibiotic policies [35]. Although surgical site infections are typically perceived to be an exogenous problem related to exposure to healthcare workers, the most causative pathogens are endogenous from patient's own skin or mucosal flora [36,37]. Nasal carriage of SA has been identified as a potential risk factor for DSWI [38], and genetically identical SA from nasal flora have been cultivated from sternotomy wounds [39]. Unlike SA which caused a more aggressive presen‐ tation, CONS infection accompanied with bacteremia as observed in 50-60% of cases [34, 40] had a rather indolent course, clinically manifested later, and was more prone to recurrence [41, 42]. DSWI is diagnosed in 40-70% of patients post-discharge, thus post-discharge surveillance of up to 90 days is recommended [43]. Gram negative strains contribute less commonly in the pathogenesis of DSWI and mostly translocate from other host site infections, such as pneu‐ monia, urinary or abdominal infections [34]. Finally, no significant difference in mortality was observed between DSWI infections caused by CoNS, when compared to SA, or Gram-negative pathogens [34]. Mekontso-Dessap et al suggested that DSWI caused by methicillin-resistant SA (MRSA) may have worse actuarial survival than sensitive strains (MSSA) in terms of 1 month, 1-year, and 3- year survival (60.0%±12.6%, 52.5%±-3.4%, and 26.3%±19.7% versus 84.6% ±7.1%, 79.0%±8.6%, and 79.0%±-8.65, p=0.04), and a regression analysis revealed MRSA as an

Unsurprisingly, DSWI negatively affected outcomes in cardiac surgery. Even with the adoption of modern treatment strategies, the reported in-hospital mortality for DSWI varies from 1.1 to 19% [6-9,11,16,45]. Although the mortality rate is similar to data reported from the 1980s, it appears that implementation of negative pressure wound therapy (NPWT) may improve long-term survival of patients [18,20,46]. Regardless of treatment strategy, in-hospital stay of DSWI patients is at least two weeks longer compared to patients with an uncomplicated post-operative course [6,10,11]. DSWI-related morbidity was repeatedly reported in relation to prolonged mechanical ventilation, renal impairment, atrial and ventricular arrhythmias, cerebrovascular accidents, need for hemodynamic support, and healing-related complications [20,47]. The cause of death in the early post-operative period is mostly multiple organ failure initiated by sepsis or specific DSWI-related complications such as serious bleeding [6-8,16,18, 20]. Predictors of a poor outcome in DSWI patients that have been reported include length of intensive care unit (ICU) stay, late indication for surgical revision, bacteremia, hemodynamic instability, and prolonged mechanical ventilation [47,48]. Loop et al presented the worse survival data of DSWI in patients operated on during the 1980s in comparison with a standard CABG population within a 3-year follow-up after surgery [6]. Survival analyses published in


**Table 3.** Analyses of compared mid-term and long-term survival of patients with DSWI with non-DSWI patients

Patients who develop DSWI are 2.5 to 3 times more expensive to manage compared with patients who have an uncomplicated post-operative course [6,11]. The first calculation of cost originated from the Loop et al paper, published in the late 1980´s, and found a 2.8 times increase in cost [6]. Patients who died of DSWI consequences consumed 60,500 USD more, making the total cost of these patients approximately 80,000 USD compared with 11,000 USD an uncom‐ plicated CABG patient cost, as showed by Hollenbeak et al [11]. Recent data from Germany showed a doubling in cost (36,261 vs. 13,356 EUR, p<0.001) for DSWI patients [49], while Ennker et al calculated a 9,000 EUR increase in cost on average for any DSWI case [50]. The majority of the increased cost is spent on repeat surgical and ICU service, and extension of inhospital stay [11,51,52]. In looking for cost-effectiveness of treatment strategies, NPWT does not seem to be a more expensive treatment in comparison with the conventional therapy for DSWI, as calculated in the Swedish healthcare system by Mokhari et al [52]. Atkins et al reported lower NPWT costs than Medicare charges for conventional therapy (152,000 vs. 300,000 USD) of DSWI [53].

popular [38,39]. The use of chlorhexidine for skin care before surgery showed a significant reduction in the microbial count including SA [63]. In comparison to general surgery where reduction of SSI´s due to skin decontamination was confirmed [64], data for cardiac surgery is lacking, nevertheless, protocols involving chlorhexidine or a different skin cleanser are already widely accepted. Locally applied ointment containing mupirocin is 80 to 90% effective in eradicating all types of SA from the nasopharyngeal mucosa [65]. Cimochowski et al reported about the efficacy of this practice on reducing DSWI rates from 2.7% to 0.9% [66]. A randomized controlled trial published by Konvalinka et al did not confirm a reduced DSWI

Current Challenges in the Treatment of Deep Sternal Wound Infection Following Cardiac Surgery

http://dx.doi.org/10.5772/55310

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The surgical technique in performing median sternotomy and its closure certainly influences the risk of DSWI. Careful handling of skin and pre-sternal soft tissue, mid-lined sternal incision and avoidance of bone wax are essential, in addition to keeping scrub protocol, checking for glove injury, changing gloves after sternotomy and after sternal wiring, and leaving the closed

It has been proposed that the method of IMA harvesting affects the incidence of DSWI, particularly when both IMA (BIMA´s) are demanded for revascularization [7,8,10,27,28]. A recent meta-analysis published by Saso et al showed a reduced risk of SWI´s once IMA or BIMA´s were harvested in a skeletonized fashion compared with a pedicled graft. The risk was reduced both in the non-diabetic (2.96% vs. 11.7%) and diabetic populations (2.4% vs. 14.2%) [69]. Besides harvesting methods of BIMA´s in diabetics, as was mentioned above, tight longterm glycemic control influenced the risk of DSWI. A hemoglobin A1c (HbA1c) ≥7% had a higher incidence of DSWI compared with patients who had a HbA1c <7% (5.0% vs. 1.4%, P = 0.014). A 31% increased risk of DSWI (OR = 1.31, 95% CI 1.16-1.49, P < 0.001) was seen by Halkos et al [26]. Even through diabetic patients may have a comparable risk of developing DSWI when IMA in skeletonized fashion is taken down, the BIMA´s harvesting need is to be considered carefully because additional risk factors such an obesity and COPD are commonly

The crucial point in preventing DSWI is achievement of stable sternal approximation. Standard sternal wire cerclage, if performed well, is fast, easy and effective [71]. Facing poor sternal quality, sternal fracture, or increased traction forces in obese or COPD patients, some modifi‐ cations of this technique were proposed. Parasternal wire reinforcement, described originally by Robicsek and modified by Sharma, proved to reduce the risk of sternal wound complica‐ tions [72,73]. Friberg et al reported that the use of more than 6 or 7 simple wires may also reduce DSWI rates (0.4% vs. 4.2%, p=0.001) [74]. Recently, a large multicenter prospective study conducted by Schimmer et al comparing the Robicsek technique with standard cerclage failed to reduce the risk of SWI and sternal dehiscence [75]. Primary plating, mirroring the experience in maxillofacial surgery, was proposed for patients at high risk of sternal non-union [76]. Plates could be anchored only into the sternal bone (SternaLock system™,Biomet Microfixation Inc, Jacksonville, US) or into the ribs (Titanium Sternal Fixation system™, Syntes, Switzeland). Raman et al reported better chest bone healing after primary plating than rewiring at 6-month follow up (70 vs. 24%, p=0.003) and lower pain scores, with no difference in SWI rates [77]. Others systems are used for sternal approximation including, thermoreactive nitinol clips

rate from the use of nasal mupirocin ointment (0.8 vs. 0.8%) [67].

wound primarily covered for at least 48 hours [68].

presented in this cohort [24,70].
