IJCS | Volume 31, Nº2, March / April 2018

169 Considering the trans- and postoperative variables, it was also demonstrated there was no consensus on the risk factors associated withmediastinitis. The increase in the time of post-surgical hospitalization and occurrence of fever after surgery were more common in patients with mediastinitis. The mean creatinine level was also considered an independent and higher risk factor in patients with mediastinitis. Other trans-operative and post-surgical risk factors, such as the use of pediculated internal thoracic arteries and CABGwith ECC, have also been mentioned in the literature 1 , as well as a mammary bridge when associated with obesity. 8 However, in this study, no difference was observed between the groups in relation to ECC (p = 0.770). The trans-operative period of cardiac surgery is critical because of its complexity and the procedures inherent to it, such as ECC and prolonged intraoperative time. Several factors influence the onset of surgical wound infection, such as invasive procedures and insufficient primary defense caused by surgical trauma and ECC, which, in turn, causes physiological changes in the immune system, especially due to the use of hypothermia and hemodilution, predisposing to the onset of infections. 31 Health professionals should be aware of them and prepared to intervene in situations of fluid volume imbalance, impaired gas exchange, protection changes due to coagulation system inhibition with systemic heparinization and sequestration of leukocytes from the circulation. 32 As for the bacteriological diagnosis in this study, the most prevalent among gram-positive bacteria was Staphylococcus aureus (30.7%) in patients with mediastinitis. High occurrence of Gram-positive bacteria (46.2%) was also observed. Studies carried out in Brazil indicate Staphylococcus aureus as the predominant causal agent inmediastinitis. International studies have shown a predominance of Staphylococcus epidermidis and a variety of Gram-positive bacteria in 40% of cases. 33 Fungal infections are infrequent. 34 Staphylococcus aureus and Staphylococcus epidermidis account for 70% to 80% of cases. 35 The presence of Staphylococcus aureus causes the infections to show a rapid clinical course and more aggressive characteristics; therefore, its elimination and the care required by the surgical team during the preoperative period are of utmost importance. In the study by Gib et al. 36 , who carried out a study in patients with postoperativemediastinitis, Staphylococcus aureus was also themost prevalent microorganism (58.1%). The same was observed by Sá et al. 5 , who evaluated the files of patients undergoing cardiovascular surgery from 2007 to 2009. The culture of the exudatewas positive in 84%of the cases of mediastinitis, with Staphylococcus aureus being themost often identified pathogen (28.8%). Souza et al., 4 who evaluated the files of patients submitted to cardiac surgeries between 1991 and 2000, verified that Staphylococcus aureus was the most frequently isolated microorganism from the surgical wound (46.0%), followed by Pseudomonas aeruginosa (21.6%) and Staphylococcus epidermidis (8.1%). The cases with Staphylococcus epidermidis isolation developed chronic mediastinitis. Charbonneau et al. 37 carried out a study in patientswith cardiacmediastinitis admitted to the ICU from2000 to 2008 in two hospitals in France, and found that 309 patients developed post-sternotomymediastinitis, of which 29.4% hadGram-positive bacteria. The presence of Gram-positive bacteria was associated with drainage failure, secondary infection, need for prolonged mechanical ventilation and/or use of vasopressor agents. There are several possibilities regarding the entry points for pathogens in patients submitted to thoracic or cardiac surgery, such as the sternal irrigation impairment using internal thoracic arteries during myocardial revascularization, use of prostheses in contact with the bloodstream, organic weakness and, in some cases, poor hemodynamic status in the patients' postoperative period, causing low immunological deficits, especially in diabetic, and elderly patients and/or those with severe myocardial dysfunction. 10,38 Thus, preventive measures 39 are crucial to avoid patient colonization by microorganisms, such as reducing hospitalization time, especially before surgery, avoiding colonization by microorganisms selected from the hospital environment; performing stringent patient asepsis; using the electrocautery as little as possible in the dieresis; handling tissues carefully; avoiding surgical trauma to the sternum as much as possible; performing rigorous hemostasis; periodically guiding the team and evaluating the equipment used in the surgical center or in the ICU; in addition to adequately handling drains, catheters and operative dressings. This study had as limitations the short period of evaluation of an infection with low prevalence, which resulted in the recording of few cases. The use of Pinto et al. Factors Associated with Post-Sternotomy Mediastinitis Int J Cardiovasc Sci. 2018;31(2)163-172 Original Article