Management of Deep Sternal Wound Infection

Abstract

Postoperative mediastinitis is defined as a deep sternal incisional surgical site infection which identified by culture of an organism, histopathological examination or presence of at least one of the main signs or symptoms of infection. There are 5 subtypes of postoperative mediastinitis based on the time of first presentation, the presence or absence of risk factors, and failure previous attempts of closure. In type I and II risk factors are absent while it present in type III. Types IV and V are chronic types. The incidence of postoperative mediastinitis is variable ranged from 1-12%. The most common causative pathogen involved in sternal wound infections is Staphylococcus epidermidis and Staphylococcus aureus. Median sternotomy wound infection starts as a localized area of sternal osteomyelitis or it starts due to inadequate mediastinal drainage, leading to a large retrosternal collection acting as a culture medium for bacterial growth. Host risk factors for mediastinitis after cardiac surgery include diabetes mellitus, obesity, and extended preoperative hospital length of stay. Perioperative risk factors include use of intra-aortic balloon pump or other inotropic support, excessive SUMMARY 121 aortic cross-clamp and by-pass time, re-exploration or emergent surgery, prolonged post-operative mechanical ventilation, and concurrent saphenous vein graft harvest site infection. Several other procedures such as pre-operative chest hair removal by razor shaving, reliance on electrocautery for dissection, and use of bilateral internal mammary arterial grafting in diabetics have all been associated with increased risk of deep sternal wound infections. Recommendations for prevention of mediastinitis include: hand hygiene, longer and broader-spectrum antibiotic prophylaxis, blood glucose control in cardiac surgery patients with diabetes, pre-operative hair removal, meticulous skin antisepsis, aseptic technique, meticulous hemostasis and treatment of intra-operative coagulopathies, optimal postoperative dressing, preoperative skin cleanliness, nasal decolonization and stable sternal approximation. The diagnostic criteria for an organ/space infection include purulent drainage, positive microbiology, and an abscess or other observable evidence of infection. Blood cultures should be performed in patients with a temperature above 38°C after the first 48 hours following operation. Microbiological culture is often required to confirm the clinical diagnosis. Chest X-ray is rarely helpful in the early diagnosis of mediastinitis. Chest CT scanning with mediastinal aspiration can offer valuable SUMMARY 122 information for diagnosis and treatment, and it is useful for assessing the extent of mediastinal infection. Scintigraphy with WBCs or granulocytes labelled with both 111In and 99mTc-hexamethylpropylene amine oximes (99mTc-HMPAO)are preferred in the diagnosis of sternal infections. Superficial infections are treated by simple incision, drainage, and open dressing changes. Deep sternal wound infections are harder to manage. Several approaches have been used. A single procedure that can be applied successfully to all cases of mediastinitis does not seem to exist. An empirical antimicrobial therapy should be considered and include agents active against gram-negative organisms and methicillin-resistant gram-positive organisms as well as metronidazole. Several surgical techniques were developed over the last decades: open wound dressing, closed irrigation, closed suction drainage and more recently, vacuum-assist drainage. There are multiple methods of closed wound irrigation including: antibiotic irrigation, povidone-iodine (antiseptic) irrigation, irrigation with electrolyzed strong acid aqueous Solution, and use of multiple irrigation-suction system. A variety of primary sternal closure techniques at reoperation have