الفهرس 
AnatomyOnly 14 pages are availabe for public view
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Abstract
SUMMARY
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
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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
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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 been devised to avoid problems with loose wires. Such techniques include creating lateral and
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longitudinal wire support, combining it with pectoralis major advancement flaps and modification of the figure-of-eight pericostal closure technique.
Rigid fixation with metal plates and screws results in two-dimensional support and speed bony healing across the linear sternotomy. Some surgeons prefer rigid fixation rather than wire circulage if the patient was at high risk for sternal dehiscence as in obese patients.
Recent studies showing promising results that Vacuum-assisted closure provides a safe and effective adjunctive method for treatment of postoperative mediastinitis. This therapy stimulates granulation tissue formation in combination with an increased blood flow in the adjacent tissue and approximates the wound edges with a low degree of surgical trauma.
Hyperbaric oxygen therapy delivered by means of a hyperbaric chamber cab be used to improve ischaemic hypoxia of sternal infection and may improve clinical outcome when combined with surgical treatment.
Reconstruction of Infected Sternal Wound with Flaps may be influenced by various clinical situations, individual preferences, and experience. The omental flap easily fills the cavity and obliterates the dead space, however the greatest disadvantage of the omental flaps is linked to postoperative pain
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and considerable surgical trauma following laparotomy, which can be reduced using laparoscopically harvested omental flap.
Recently, some authors recommended pectoralis major muscle flap as the first choice. Pectoralis major muscle flap may be pedicled or free. Muscles provide material to close the defect and obliterate the potential dead space, however the disadvantage of the pectoralis muscle flaps is the resulting compromise in the functionality of the shoulder girdle.
The rectus abdominis transposition flap has proved to be effective for reconstruction of deep or lower sternal defects. The combined pectoralis major and rectus abdominis bipedicled muscle flap has a good blood supply and completely covers the sternal defect. For wounds at upper half of sternum the pectoralis major muscle flap is recommended and for defects in the lower half and whole sternum the combined pectoralis major and rectus abdominis bipedicled muscle flap is recommended