IJCS | Volume 31, Nº2, March / April 2018

168 incidence within the reference values indicated by the ACC/AHA guideline. 11 Regarding mortality, high rates have been described in the literature, with rates ranging between 14% and 47%. 3 In Brazilian studies of patients submitted to cardiac surgeries, mortality rates ranged from 15.8% to 42.8%. 1,3,4,6,8,15 . An international study showed a lower mortality rate (9.1%), 17 but it was higher in patients who developed mediastinitis 17 as observed in the present study. This variation suggests that both the incidence of mediastinitis and mortality rates may be related to the evaluated institution, andmay be influencedby the routine of the institution, the use of prophylactic antimicrobials or the standardization of aseptic techniques. Regarding the preoperative risk factors, no significant differences were observed in this study when the factors were evaluated alone, as in the previous study performed in this same institution. 15 However, in the logistic regressionmodel, a greater chance of developing mediastinitis was attributed to the higher number of preoperative risk factors. Each increase of one risk factor increased the chance of having mediastinitis by 57.3%. A literature review aimed to identify the risk factors associated to the occurrence of post-sternotomy mediastinitis in adult patients submitted to CABG. The main risk factors identified were age over 65 years, DM, obesity, COPD and surgical reintervention. 20 Tiveron et al. 16 verified the pre-operative risk factors in patients (most submitted to CABG) and the occurrence of mediastinitis, and identified intra-aortic balloon, hemodialysis and extracardiac vascular intervention. Oliveira and Paula 21 found DM, hospitalization time of more than seven 7 days preoperatively, smoking and obesity as risk factors. Guaragna et al. 8 evaluated patients submitted to cardiac surgery, and the preoperative risk factors were: obesity, DM, COPD, previous cardiac surgery, smoking and gender – with obesity, COPD and DMbeing independent risk factors, even when analyzed by gender and age. A study carried out in patients submitted to CABG showed independent preoperative risk factors related to mediastinitis, such as DM, obesity and smoking 1 . In a study carried out in the UK, 17 the following factors were listed: age, body mass index, DM and COPD. Many risk factors have been associated with the development of mediastinitis after cardiac surgery. However, it has been observed there is no definite consensus about the most important risk factors associated with mediastinitis, nor even if each factor can be considered an independent predictor of risk in the postoperative period. In general, the studies only describe the main risk factors associated with the disease in different health services. 22 Studies carried out in different health services 1,8,17,21 showed similar results to those observed in the literature review, 20 which showed age, DM, obesity, surgical reintervention and COPD as the main risk factors related to the occurrence of mediastinitis in adult patients submitted to CABG. COPD was identified as a risk factor for mediastinitis by Ariyaratnam et al. 19 and Guaragna et al., 8 who emphasize that patients with COPD are more susceptible to surgical wound infection due to tissue hypoxemia and the need for corticosteroid therapy in the pre- and/or postoperative period, facilitating the onset of infections. Another risk factor related to mediastinitis is obesity, although it shows controversial results in cardiac surgeries. 23 Obese patients may have worse evolution when submitted to major surgeries. Obesity can impair the healing of the surgical wound, due to the rupture of the surgical sutures, facilitating bacterial invasion of the surgical site. 23-25 This is due to the propagation of high lateral traction forces at the edges of the skin incision in the supine position, as well as the folding of the skin in the distal third of the surgical incision in the inframammary region (area of extensive colonization of microorganisms) in the sitting position. 26 Since obesity is a modifiable risk factor, it is important that measures for weight reduction be adopted in the preoperative period. Additionally, it must be considered that obesity can make it difficult to adjust antibiotic doses to the body mass, consequently leading to low tissue concentrations of the antibiotic. 27,28 In this study, the association between obesity and mediastinitis (p = 1,000) was not observed. Two studies 1,8 demonstrated that obesity and DM were associated with the occurrence of post-sternotomy mediastinitis. A multicenter study, called the Parisian Mediastinitis StudyGroup, 29 also verified this association, in addition to showing that obesity was the only independent risk factor for mediastinitis. Regarding DM, Ledur et al. 30 declared that high glucose levels were associated with an increase in the inflammatory process, leading to a significant increase in infection and organ dysfunction. 30 Smoking, mainly associated with COPD, has also been considered one of the risk factors associated with mediastinitis. 6 Some authors 1 found smoking as an independent risk factor for the development of mediastinitis. Pinto et al. Factors Associated with Post-Sternotomy Mediastinitis Int J Cardiovasc Sci. 2018;31(2)163-172 Original Article