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Ann Thorac Surg 2001;72:1411-1418
© 2001 The Society of Thoracic Surgeons
a Department of Plastic Surgery, St. John’s Mercy Medical Center, St. Louis, Missouri, USA
b St. Louis University School of Medicine, St. Louis, Missouri, USA
Address reprint requests to Dr Francel, 621 S New Ballas Rd, Suite 1009B, St. Louis, MO 63141
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Abstract |
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 Top Abstract IntroductionMaterial and methodsTreatment optionsReconstructive optionsCommentReferences |
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Introduction |
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TopAbstractIntroductionMaterial and methodsTreatment optionsReconstructive optionsCommentReferences |
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The incidence of poststernotomy mediastinitis is distorted by poor delineation of the true depth and extent of the infection. Two articles from the same institution presented widely divergent rates of infection over a similar time interval (2% versus 9%) [2, 3]. Often these differences result from mixed reporting by combining deep serious infections and minor superficial wound problems as poststernotomy infections. This article will specifically deal with deep infections of the mediastinum with a separate presentation for superficial wound problems.
The rate of superficial wound infections should be the expected rate after any clean surgical procedure (approximately 2%) [4]. The complication rate of mediastinitis after midline sternotomy irrespective of procedure is 1% to 4% [5–12]. When the incidence is higher, a careful evaluation and correction of probable causes should be embarked upon to reduce the risk to the patient. Some correctable occurrences include off midline sternotomies, long cardiopulmonary bypass times, infected hospital personnel, prolonged postoperative ventilation, contaminated hospital equipment (ventilators), and other infections, such as peripheral phlebitis, urinary tract infections, and pneumonia [2, 8, 10, 12–14]. With vigilance and quick corrections, an acceptable incidence should be achieved regardless of patient population.
Prevention of these infections is important since morbidity and mortality is high [15–18]. The cost of hospitalization for mediastinitis increases approximately three times above the usual cost for coronary artery bypass graft or approximately $60,000.00 more per patient [8]. Prevention measures include true midline sternotomy to preserve periosteal blood flow, limiting internal mammary artery (IMA) harvest and length [19], avoiding IMA harvest in high risk patients [20], avoiding foreign bodies (bone wax) that may impede osseous union and harbor bacteria [21], accurate and precise reapproximation of sternal halves, perioperative broad spectrum antibiotics, and close monitoring of hospital equipment and personnel.
Although the incidence of poststernotomy mediastinitis is low, there is a significant presence of these complications, especially in centers that perform large numbers of sternotomies. The high mortality rate (20% to 50%) and morbidity rate (approximately 50%) necessitate rapid and aggressive treatment of this potentially fatal complication. This article will use years of experience and patient numbers to analyze the problem, address treatment of reconstructive options, and present long-term results that will assist the surgeons and the reconstructive surgeon to correctly diagnose the problem and successfully control the infection. Cooperation and understanding between the treating physicians will limit the anxiety of the patient and hasten recovery.
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Material and methods |
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TopAbstractIntroductionMaterial and methodsTreatment optionsReconstructive optionsCommentReferences |
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Our approach as developed over years of experience is summarized in Figure 1. The flow diagram will assist in the evaluation of any patient returning with wound difficulties after sternotomy.
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In superficial soft tissue infections the most common presentation is an area of pointing in the incision. There is surrounding erythema and tenderness but it is localized. The infection is superficial to the anterior table of the sternum. Bimanual firm palpations of the sternal halves reveal no sternal instability, movement, pain, or clicking as the bone edges are stable (Fig 2). Sternal instability usually signifies a deeper process.
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The resulting wound should be carefully inspected to determine the extent of soft tissue involvement. The soft tissue layer of closure over the sternum is commonly maintained and neither bone nor wires are exposed. Irrigation with peroxide or povidone iodine and dressing changes are indicated. The wound should show signs of healthy healing granulation tissue within 24 to 48 hours. Healing should be complete in about 2 to 3 weeks depending upon the wound size.
The treatment is not as straightforward if the soft tissue layer is violated and there is exposed bone or wires. Exposed bone may deteriorate and desiccate outside of a moist environment. If the local infection is drained and under control, a colloid dressing will keep a moist environment over the bone, prevent desiccation, and encourage the growth of healthy granulation tissue. The treatment is more controversial if wire is exposed at the base of the wound. Although these may heal if the local environment is hospitable, this foreign body must be considered contaminated and may cause late problems (nonhealing sinus tracts, wire track bone sequestration). If the rest of the sternum is well-approximated and stable, then wire removal may be indicated to prevent later morbidity. The wire may be maintained if it is felt necessary to encourage healing between the two hemi-sternums and late removal of this previously exposed wire after bone healing may lessen complications.
Intravenous analysis of deep infections (mediastinitis)
Patients with mediastinitis should be rapidly and correctly diagnosed, aggressively treated, and watched carefully for life-threatening complications. The presenting symptoms may vary depending upon the extent of involvement but a patient with ongoing sternal pain should be carefully evaluated before establishing the diagnosis of sternal nonunion to account for the pain. A patient with chest pain after a well-approximated sternal split usually has a precipitating condition that does not allow bone healing. Laboratory testing and radiographic evaluation may be necessary to diagnose an early deep infection.
Early presentations of 7 to 10 days
Early infections usually present before discharge or soon after the patient returns home. Often there is a serous drainage that comes from the incision approximately 4 to 5 days after sternotomy. This is frequently overlooked because the patient is otherwise progressing well. Once the infection becomes established (7 to 10 days postoperatively), the patient presents with fever, chills, lethargy, leukocytosis, and pain. The incision may remain closed but more commonly an area has not healed and drains purulent material. The surrounding skin is usually erythematous and may be the only visible sign of an underlying infection (Fig 3).
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A CT scan is indicated if the sternum is stable. The CT scan may show an undrained poststernal collection or a retrocardiac abscess, especially if the patient is showing systemic signs of sepsis. Operative intervention is needed if the sternum is unstable. A CT scan may still be beneficial to evaluate the retrocardiac space.
Late presentation of 10 to 30 days
The most common time period for presentation of mediastinitis poststernotomy is approximately 10 to 30 days. The patient usually has been discharged from the hospital but returns complaining of pain, an increase in purulent drainage, and lethargy because of the inability to sleep secondary to pain while lying on their side. Presenting signs include fever, leukocytosis, partial disruption of the incision with purulent drainage that may necessitate with direct pressure, and a grossly unstable sternum with bimanual alternating chest compressions. If there has not been a dissipation of infection, the patient may present with signs of sepsis requiring blood pressure and assisted ventilation but this is unusual.
The need for a CT scan with this presentation may be helpful only to evaluate areas of undrained sepsis (eg, retrocardiac, empyema). Computed tomographic scans in this population usually show the expected signs of a mediastinal collection with air, and operative drainage is indicated. A CT scan in a patient with less impressive symptoms and signs (eg, drainage but a grossly stable sternum) may be difficult to interpret because of normal postoperative changes in the mediastinum. Still it is recommended to evaluate other sources of infection (subphrenic area, pleural space).
Operative drainage is indicated with sternal instability. The wires are removed, sternal halves are separated with care to prevent injury to fixed underlying structures, and the mediastinum is inspected.
Late presentation of more than 30 days
The most difficult population of patients to evaluate and treat are those more than 30 days after their sternotomy. They rarely present with overt mediastinitis unless it is a highly virulent bacteria that has been smoldering, or with signs of lesser tissue involvement that have been ignored and have a superficial infection that has progressed to the deeper structures. This is especially seen when inferior infections around the xiphoid process have extended into the mediastinum because of inadequate external drainage.
Often these patients present with open draining wounds without sternal instability. A large portion of the sternum may have healed allowing chest stability. Close examination of the wound reveals signs of substernal involvement with purulence necessitating around (1) loose wires, (2) at the costal sternal junction between the cartilage, or (3) through a large inferior sternal defect. The patient’s only complaint may be the drainage. They may have very little pain if a large portion of the sternum is stable. The sepsis is drained, therefore they rarely have fever, chills, leukocytosis, or systemic signs or symptoms. The bacteria cultured tend to be more mixed nonvirulent forms.
A CT scan is particularly helpful in these patients as it may best define involvement of the bone and soft tissue. Most commonly, we have seen the superior sternum and mediastinum heal but the lower sternum and costal cartilages involved with the underlying right ventricle isolated from the infected tissue. Treatment of these cases is particularly hazardous because the superior mediastinum is healed and there is difficult access to great vessels. Therefore, if debridement is required, the patient should be prepared for cardiopulmonary bypass through the peripheral vessels.
Operating room debridement
Operating room debridement should be undertaken once it is determined that the sternum is unstable or there is undrained sepsis. Simple wire removal may be performed in a controlled setting, but the operating room allows for safer conditions to evaluate the mediastinum. The sternal wires should be removed, careful dissection performed to divide adhesions between the sternal bone and underlying structures, cultures taken of any fluids present, and a careful inspection of the mediastinum performed. Inspection should include the spaces between the great vessels, the retrocardiac space through an inferior supradiaphragmatic approach, and an evaluation of the left pericardial space above the right and left ventricle. This evaluation is greatly assisted by the preoperative CT scan. If no collection is seen on the CT scan and the space appears healed without evidence of purulent material, then dissection of the area may not be indicated. Attempted exploration of a closed, healed space carries an extremely high morbidity and may be avoided based on the preoperative CT scan and intraoperative clinical evaluation.
Any fluid encountered should be sent for immediate Gram stain and culture. The Gram stain may be helpful in deciding treatment options to be discussed later. The sternal bone should also be carefully evaluated. If all of it appears viable, a bone biopsy at this time may be helpful to determine the appropriate type and duration of antibiotics. Any nonhealing bone should be removed at this initial debridement but should be done conservatively. Distinguishing characteristics of healthy bone include firmness, bleeding from the cut edges, and a crisp snap with rongeur debridement.
Intraoperative evaluations at initial debridement
After the opening of the hemisternum, drainage of collections, and bone debridement, a treatment plan needs to be formulated. The following evaluations are helpful in determining the course of therapy.
Gram stain
If the Gram stain does not reveal any bacteria, then a more aggressive approach to sternal closure may be undertaken.
Purulence and exudate
The presence of gross purulence may be a directive to conservative therapy. Dressing changes to control the infection and encourage healthy granulation tissue are appropriate if the mediastinal structures are covered with a thick exudate.
Depth of mediastinal involvement
The volume of dead space separating the mediastinal structures and the posterior table of the sternum will help determine whether secondary healing may be accomplished within a reasonable time. Extensive dead space needs to be corrected according to good surgical principles to encourage healing.
Sternal bone involvement
The options for direct closure of the hemisternum remain if the bone is healthy enough to allow rewiring without fracture.
Prosthetic material
The exposure of prosthetic material needs to be evaluated. Small unnecessary pledget fragments should be trimmed. If a foreign body is incorporated into the healthy tissue, then it can usually remain undisturbed. Exposed great vessel replacement needs special consideration as discussed later.
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Treatment options |
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Sternal bone uninvolved without purulence
If the sternum is viable and there is no gross purulence, then sternal rewiring over drains is appropriate (Fig 4). Cultures of any fluid in the mediastinum are taken, and a bone biopsy is sent for analysis. Pressurized pulsatile antibiotic irrigation of the mediastinum, sternal edges, and the subcutaneous space is performed. The surgeon determines the choice of drain but generally at least two and probably three drains are required. This will provide inflow and outflow as indicated. The sternum is then rewired. A Robiscek weave is often used to distribute the force of sternal closure over a widened area and prevent wires from pulling through the bone. Others have recommended strap closure (metal or other) to distribute the tension.
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Sternum is necrotic but without purulence
Sometimes examination of the mediastinum reveals no purulence or infection. The sternal dehiscence is a result of poor sternal bone healing and pulling through of the sternal wires. The Gram stain is negative for bacteria but rewiring of the sternum is not possible because of lack of adequate bone stock even for a Robiscek weave. Often the bone itself is necrotic and requires debridement or the sternum has fractured to such an extent to make rewiring impossible.
We have used immediate muscle reconstruction in these situations. This is a decision made with agreement of both the cardiac and reconstructive surgeon. Both surgeons must agree that the mediastinal environment is hospitable to muscle flap reconstruction and that there is no source of undrained sepsis. The sternum is debrided, pressurized pulsatile vancomycin irrigation is used (typically 3 L), and the reconstruction is performed over drains. Close postoperative surveillance is required to rule out any ongoing infection. This has been possible in 42% of our patients.
Purulent mediastinal collections
The status of the sternum is immaterial if there is gross purulence encountered in the mediastinum. These situations are best treated with drainage, wound care, and secondary reconstructions. Primary reconstructions over uncontrolled sepsis have a high morbidity and mortality and should be considered only in extreme conditions as discussed later.
The mediastinum is inspected and all suspicious areas are carefully drained. There is a risk of right ventricle laceration if the sternum is left open. A right ventricular laceration is associated with high morbidity and mortality rates [22–24]. Early in the series we had four patients sustain a right ventricular laceration after sternal debridement and packing. A 25% mortality was observed in these patients. Three patients were fortunate enough to return urgently to the operating room for repair, which included a fascial graft harvested from the pericardium or the anterior rectus sheath and immediate flap reconstruction using the rectus muscle in two patients and the omentum in the third patient. The reconstruction is placed in intimate contact with the fascial graft to promote revascularization of the graft from the surrounding well-vascularized flap tissue [24–26]. Follow-up transesophageal echocardiogram has shown no aneurysm at this repair site. This is probably the result of the healed reconstruction flap adding support. The transesophageal echocardiogram has also shown good right ventricular wall function. We therefore believe that immediate reconstruction is indicated in these extreme complications. We have been able to avoid this complication over the last 4 years by using the following protocol.
The potential etiology of this complication needs to be addressed before packing the open mediastinum and leaving the operating room. This involves freeing adhesions between the right ventricle and left hemisternum and removing any bone spicules that may be protruding from the cut edges of the sternum. Packing should be placed between the sternum and the right ventricle to avoid friction with heartbeats.
A decision needs to be made regarding extubation before leaving the operating room if the sternum is left open. A potential cause for right ventricular laceration is increased thoracic pressure when the patient struggles against the endotracheal tube. The right ventricle is forced between the sternal halves and as the ventilator removes air the chest collapses. The right ventricle is caught between the sternal edges as they come together and the risk of right ventricular laceration is high. Therefore, when patients cannot be extubated and require mechanical ventilation, our patients have remained intubated, paralyzed, and sedated until final reconstruction can be completed.
Successful reconstruction in these patients can usually be accomplished over the next few postoperative days. A physician skilled in wound management must perform the first dressing change 12 to 24 hours after debridement. This is an important time to evaluate the wound. The dressing is removed carefully from the mediastinal structures and inspected. Gross purulence on the dressing is commonly seen with ongoing infection and an inhospitable environment. Collections previously undrained may spontaneously drain into the dressing. The purulence is inspected for characteristics that may dictate dressing solutions (eg, Dakin’s solution or acidic acid solutions for pseudomonas infection, povidone iodine for a Staphylococcal infection, kanamycin for gram negative infections). Dressings should be changed at least twice a day until the dressing no longer contains purulent material and a healthy granulation is starting to develop and replace the exudative surface. Secondary reconstruction is then considered if the patient remains afebrile and has no signs of ongoing sepsis.
Presence of significant exposed foreign material
The presence of significant exposed foreign material in an infected mediastinum is a difficult problem. As stated previously, foreign material incorporated into healthy tissue does not need debridement. Sometimes it may be beneficial to remove unincorporated material and replace it with sterile material. Some foreign material is impossible to remove because the surrounding tissue is so indurated that replacement would have an extremely high morbidity and mortality. This is most common in cases of mediastinitis after root, arch, and thoracic aortic replacements. It has been our preference in these cases to irrigate the foreign material with 3 L of vancomycin antibiotic solution and wrap the great vessel graft with an omental pedicle flap to encase the graft completely with healthy, vascularized tissue. The omentum is best suited for this reconstruction because it is malleable, has excellent blood flow, and is replete with polymorphonuclear cells. The sternum is then either rewired or left open with muscle, soft tissue, and skin closed over the omental-filled mediastinum.
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Reconstructive options |
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TopAbstractIntroductionMaterial and methodsTreatment optionsReconstructive optionsCommentReferences |
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Comment |
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TopAbstractIntroductionMaterial and methodsTreatment optionsReconstructive optionsCommentReferences |
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We have not found the harvest of the IMA to significantly contribute to poststernotomy infections. A limited IMA dissection has been performed as previously described [19]. The patient selection is appropriate and the IMA harvest is not performed bilaterally in obese, diabetic patients [20]. Previous studies of the vascular supply of the sternum have shown the IMA and the periosteal branches to be a source of nutrients for the sternum [27]. Dynamic studies and radioactive mapping confirmed a relative avascularity of the ipsilateral hemi-sternum after IMA harvest [28–30]. A later study seemed to show a total revascularization after 3 weeks [31]. Most avascular hemisternums heal after IMA harvest and therefore, other contributing factors may determine whether the bone is going to heal or become necrotic. These factors include off-line sternal splits, contamination, sternal fractures, inadequate bone approximation, and prolonged ventilation dependency [32]. The presence of any of these factors along with an avascular bone may result in bone necrosis and sternal dehiscence.
A few technical considerations may be preventative, including absolute midline sternal splits, minimal interference with periosteal blood supply, and firm bone-to-bone reapproximation. The use of bone wax or other nondissolving material between the sternal edges should be discouraged. Bone wax has been known to encourage the growth of Staphylococcal bacteria [21]. The presence of this inert material may prevent bone in-growth from the healthy vascular contralateral hemisternum, especially during the early postoperative period (< 3 weeks). Removal of all bone wax before bone approximation or the use of a dissolving material may be more appropriate [33].
The flow sheet (Fig 1) highlights the important points of the decision-making process when the patient presents with a poststernotomy wound infection. It is important not to underestimate an inferior (superficial) wound infection. These infections must be drained and aggressively treated to avoid propagation of infection into the substernal space. Drainage, appropriate antibiotics, and dressing changes are appropriate treatment measures.
We have routinely employed CT scan evaluation of the mediastinum and bone to assist in the decision-making process. Although it is sometimes difficult to differentiate postoperative tissue changes from early inflammatory tissues, the CT scan is helpful to evaluate the retrocardiac space, subphrenic space, pleural space, and the superior mediastinum around the great vessels [34]. Obvious collections with air fluid levels necessitate exploration and drainage. We have used a bone scan to evaluate late infections involving the bone but do not find it particularly helpful to treat early infections. Epicardial pacemaking wire cultures [35] may be helpful to delineate patients to be carefully watched for infections but it does not help in determining treatment. An indium tagged white blood cell scan [36] may be helpful but it does not evaluate the status of the sternal bone.
The ability to rewire the sternum allows for decreased cost, decreased hospitalization, and a stable sternum [17, 37, 38]. There are associated complications related to undrained sepsis, Candida suprainfections, and failures of treatment. This procedure is best preserved for patients with shallow mediastinitis and strong remaining bone stock. The reported success rate with rewiring is approximately 80% [17, 18]. Our success rate using this principle has been 65%. The failures are treated successfully with muscle flap reconstruction although hospitalization is prolonged and recovery is extended.
Primary muscle flaps placed at the time of the initial debridements may be performed if no purulence is encountered [39]. This takes cooperation between the cardiac surgeon and the reconstructive surgeon. It has been very successful in our hands, but experience in judgments for these wounds is required. Forty-two percent of reconstructions in our series have been completed at the time of initial debridement. Patients overall have done well including the reconstructions performed urgently because of exposed foreign material and the postoperative repair of a right ventricular laceration. If there is any doubt about the hostility of the wound, it is best to perform the procedure as a delayed reconstruction and improve the wound with local care.
This present series shows excellent results after flap reconstruction with most patients requiring only one procedure to heal the mediastinal defects. This is a result of the more correct diagnosis of the defect and understanding the issues surrounding early healing. With cooperation between the cardiac surgeon and the reconstructive surgeon, the morbidity and mortality in these patients may reach more acceptable levels.
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