**5. Strategies preventing DSWI**

As mentioned previously, diabetes mellitus is a strong independent risk factor for develop‐ ment of DSWI, and concomitant obesity doubles the risk of further infection [24]. Unfortu‐ nately, both risk factors are difficult to modify. Zerr et al showed that a continuous insulin infusion started immediately after surgery to maintain a serum glucose level of 150-200mg/dl (8-11 mmol/l) led to a significant decrease in the incidence of DSWI in diabetics (2.4% to 1.5%, p < 0.02) compared with subcutaneously administered insulin [54]. A tight glycemic control protocol appears beneficial from the Portland group experience, nevertheless, decreasing serum glucose below 100mg/dl (6 mmol/l) did not bring any additional impact on DSWI rate, and was associated with a higher risk of stroke or death [55].

It has been demonstrated many times that antibiotic prophylaxis effectively prevents sternal wound infection [56]. As Staphylococcal stains are a major causative pathogen, beta-lactam antiobiotics are recommended for prophylaxis, particularly first or second generation cepha‐ losporins [57]. The use of glycopeptides, which are highly effective against MRSA, has not been linked with a reduction in sternal wound infection rates compared to standard prophy‐ laxis, with one study suggesting higher SSI´s rate (3.7 vs. 1.3%, p<0.05) when vancomycin prophylaxis was chosen [58]. Local application of a gentamicin soaked-collagen sponge between the sternal lamella was suggested to reduce all SWI´s, particularly DSWI. Friberg et al reported a significant reduction in SWI´s (3.7 vs. 9%, p<0.001), and also DSWI (1.5 vs. 3.3%, p<0.003) [59,60], however, further randomized controlled trials and meta-analyses did not confirm a benefit of using a gentamicin sponge for DSWI prevention as well as a recently published meta-analysis [61,62]. Although SA caused DSWI might be reduced by locally applied gentamicin, primarily gentamicin-resistant strains such a CONS may overgrow [62].

Another prophylactic issue is patient decontamination before surgery. As Staphylococci colonization is seen in a majority of DSWI, skin and nasopharyngeal decontamination became 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 rate from the use of nasal mupirocin ointment (0.8 vs. 0.8%) [67].

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.

As mentioned previously, diabetes mellitus is a strong independent risk factor for develop‐ ment of DSWI, and concomitant obesity doubles the risk of further infection [24]. Unfortu‐ nately, both risk factors are difficult to modify. Zerr et al showed that a continuous insulin infusion started immediately after surgery to maintain a serum glucose level of 150-200mg/dl (8-11 mmol/l) led to a significant decrease in the incidence of DSWI in diabetics (2.4% to 1.5%, p < 0.02) compared with subcutaneously administered insulin [54]. A tight glycemic control protocol appears beneficial from the Portland group experience, nevertheless, decreasing serum glucose below 100mg/dl (6 mmol/l) did not bring any additional impact on DSWI rate,

It has been demonstrated many times that antibiotic prophylaxis effectively prevents sternal wound infection [56]. As Staphylococcal stains are a major causative pathogen, beta-lactam antiobiotics are recommended for prophylaxis, particularly first or second generation cepha‐ losporins [57]. The use of glycopeptides, which are highly effective against MRSA, has not been linked with a reduction in sternal wound infection rates compared to standard prophy‐ laxis, with one study suggesting higher SSI´s rate (3.7 vs. 1.3%, p<0.05) when vancomycin prophylaxis was chosen [58]. Local application of a gentamicin soaked-collagen sponge between the sternal lamella was suggested to reduce all SWI´s, particularly DSWI. Friberg et al reported a significant reduction in SWI´s (3.7 vs. 9%, p<0.001), and also DSWI (1.5 vs. 3.3%, p<0.003) [59,60], however, further randomized controlled trials and meta-analyses did not confirm a benefit of using a gentamicin sponge for DSWI prevention as well as a recently published meta-analysis [61,62]. Although SA caused DSWI might be reduced by locally applied gentamicin, primarily gentamicin-resistant strains such a CONS may overgrow [62].

Another prophylactic issue is patient decontamination before surgery. As Staphylococci colonization is seen in a majority of DSWI, skin and nasopharyngeal decontamination became

300,000 USD) of DSWI [53].

498 Artery Bypass

**5. Strategies preventing DSWI**

and was associated with a higher risk of stroke or death [55].

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

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 presented in this cohort [24,70].

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 (Flexigrip™, Praesidia SRL, Bologna, Italy), titanium locked staples (Sternal Talon™, KLS Martin Group, US), and Poly-Ether-Ether-Ketone tapes (Sternal ZipFix system™, Syntes, Switzeland), all designed for parasteral fixation. Negri et al reported a significant reduction of mechanical dehiscence (2.8% vs. 0.2%, p=0.002), but the same risk of DSWI (1.2% vs. 2.4%) when thermoactive clips were compared with standard wire cerclage [78]. Snyder et al reported 5 years of experience with the SternaLock system™ for primary plating in high risk patients. Superiority of plate over wires was seen in the incidence of early presentation (<30 days) of SWI (0% vs. 12%, p<0.06) and shorter in-hospital stay (7 vs. 8 days, p=0.02) [79]. A pilot study published by Bennett-Guerrero et al showed insignificantly higher spirometry volume in the SternalTalon™ arm (67% ± 32%) versus the wire arm (58% ± 24%). Use of the Talon was associated with decreased use of opiates (21.3 ± 11.8 vs. 25.4 ± 21.6 mg, P = 0.44), duration of mechanical ventilation (0.5 vs. 1.0 days, P = 0.24) and hospital length of stay (4.5 ± 3.2 vs. 5.3 ± 4.0 days, P = 0.40) [80].

chest cavity following sternal debridement. It was suggested that well-vascularized omentum fulfills dead spaces, ensures high antibiotic levels, and yielded angiogenic and absorptive capacity [13,93]. Jurkiewicz et al first reported the use of muscle flaps, preferably the pectoralis flap, and radical sternal debridement in the treatment of DSWI in 1980 [94]. Consequently, 20 years of experience in the Emory group with 409 patients showed 8.1% in-hospital mortality and 5.1% primary therapy failure. 87.1% of procedures were done in single-stage fashion; the pectoralis major was used in 76.6%, rectus abdominis in 19.4%, and omentum in 2.2% [95]. This approach has received many modifications regarding the timing of wound closure, choice of flap, and type of advancement, with reported mortality ranging from 0% to 19% [96,97]. Comparing the omental to the pectoralis flap, Milano et al reported that the omental flap had lower mortality (4.8% vs. 10.5%, p<0.05), early wound related complications (9.5% vs. 27.7%,p<0.001), and in-hospital stay (10.7 vs. 18.8%, p<0.05) [98]. El Oakley and Wright suggested classification of DSWI based on the time of presentation, presence of risk factors such as obesity, diabetes or immunosuppressive therapy, and number of failed therapeutic attempts in 1996 (Table 3) [99]. The identification of five subtypes of DSWI seemed to be a relevant tool for choice of therapeutic method and patient prognosis. Adjusted to the El Oakley and Wright classification, closed chest irrigation has comparable mortality data for type I and II DSWI compared with radical sternal resection and concomitant flap, but with lower flaprelated associated morbidity [100-102]. Ringelman et al noted that at 48 month follow-up, 51% of patients had pain or discomfort, 44% had numbness, 42% complained of sternal instability, and 33% claimed to have shoulder weakness, when pectoral flap was used for reconstruction [103]. Closed chest irrigation carries a higher rate of therapy failure when used for type III, and particularly type IV and V El Oakley and Wright classification [104-107]. Thus, these patients might have benefit from more radical sternal debridement and employment of well-vascular‐ ized tissue to replenish residual defects. Flap-related morbidity may be addressed with less invasive techniques such as a laparoscopic greater omentum harvesting [108]. Atkins et al recently reported on the influence of sternal repair choice (pectoral, omental flap, or secondary

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There is limited data evaluating hyperbaric oxygen (HBO) therapy in the treatment of SWI, despite theoretical advantages, availability of HTO close to the cardiac surgical unit impedes its routine use [110]. Siondalski et al reported successful healing of 55 DSWI patients with no mortality, nevertheless therapy required 20-40 HBO sessions after surgical revision. HTO was

taken as an adjunct therapy to perform radical debridement and muscle flap [111].

Type I Mediastinitis presenting within 2 weeks after operation in the absence of risk factors Type II Mediastinitis presenting at 2 to 6 weeks after operation in the absence of risk factors

Type IIIA Mediastinitis type I in the presence of one or more risk factors Type IIIB Mediastinitis type II in the presence of one or more risk factors Type IVA Mediastinitis type I, II, or III after one failed therapeutic trial

closure) on long-term survival [109].

**Class Description of DSWI**

A promising method to reduce SSI seems to be the application of NPWT on surgically closed sternal wounds. A commercially available system (Prevena® Incision Management System, KCI, St. Antonio, USA) is used, with skin preservation through a semipermeable membrane that has contact with foam, and one proposal pump system with reservoir is added [81]. Limited clinical experience has shown a decreased risk of wound hematoma, seroma and SSI [82]. Other positive effects from wound application of NPWT might include promotion of microvascular flow and decreased tissue edema and myofibroblast activation [83]. Colli and Atkins et al reported no wound healing complications in patients at high risk for sternal wound infections after cardiac surgery, but both studies were retrospective and done on smaller cohort of patients, 10 and 57, respectively [84,85].
