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Ann Thorac Surg 1999;68:1648-1651
© 1999 The Society of Thoracic Surgeons

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Original Articles

Adjuvant treatment of deep sternal wound infection with collagenous gentamycin

^a Department of Cardiac Surgery, University of Lübeck, Lübeck, Germany

Address reprint requests to Dr Leyh, Department of Cardiac Surgery, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
Background. The treatment of deep sternal wound infections remains controversial. Currently advocated procedures carry the risk of reinfections. The significance of local antibiotic-releasing systems as an adjuvant therapy to avoid reinfections is the subject of the presented study.

Methods. Forty-two patients with deep sternal wound complication were treated with radical wound debridement, sternal refixation, retrosternal suction drainage, bilateral pectoralis major muscle flaps, and placement of collagenous drug carrier loaded with gentamycin (Sulmycin Implant) underneath, above, and between the sternal edges.

Results. No treatment failure and death were observed in our patients. Side effects after adjuvant treatment with collagenous gentamycin were not detected.

Conclusions. The preliminary results of adjuvant therapy with collagenous gentamycin in combination with surgical debridement leads to excellent results in the treatment of early deep sternal wound infections with no death and no primary treatment failures. This technique is easy to perform, reliable, and safe. For final judgment controlled randomized trials are mandatory.

	Introduction

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Sternal wound complications after cardiac operation remains to be a significant problem, despite meticulous surgical techniques. The incidence of deep sternal wound infection has been reported to vary between 1% and 1.5% in recent series with an associated mortality rate up to 27% [1–3]. Therefore, when deep sternal wound infection is detected, a rapid and effective treatment is required to avoid potentially life-threatening sequelae. Optimal treatment for deep sternal wound infection remains controversial. Continuous antibiotic irrigation, primarily described by Shumacker and Mandelbaum [4], was the treatment of choice, until high reoperation rates for persisting infections were reported [5–7]. The idea to increase the local microcirculation of the infected area by local flaps led to the development of muscle flap procedures with good results, but also muscle flap procedures carry the risk of reinfection; furthermore, the sternal edges are not reapproximated resulting in sternal instability [3, 8, 9]. Local antibiotic-releasing systems containing gentamycin as an adjuvant therapy in osteomyelitis showed encouraging results in orthopedic surgery [10]. The effect of local antibiotic administration for avoidance of reinfection in deep sternal wound infection and concomitant mediastinitis has not been evaluated. The purpose of the present study was to evaluate the possible significance of local antibiotic administration as an adjuvant treatment of postoperative deep sternal wound infection.

	Material and methods

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Clinical data
The effectiveness of adjuvant treatment with a collagenous drug carrier loaded with gentamycin for the outcome of deep sternal wound infection was evaluated in 42 patients presenting deep sternal wound infections after elective cardiac operation. Patient characteristics are summarized in Table 1. The rate of surgical morbidity after primary cardiac operation is depicted in Table 2. The patients were treated with radical wound debridement, sternal refixation, bilateral pectoralis major muscle flaps, closed drainage with Redon multihole catheters (PFM, Cologne, Germany), and, in addition to surgical therapy, collagenous drug carrier loaded with gentamycin (Sulmycin Implant Essex Pharma, Munich, Germany) was placed underneath, above, and between the sternal edges (Fig 1). Gentamycin levels from the plasma and mediastinal effusions as well as standard microbiological cultures (Table 3) from the mediastinal effluent were obtained 12, 24, and 36 hours postoperatively and then daily, until mediastinal effluent was sterile.

View larger version (46K): [in this window] [in a new window]   Fig 1. Cross-sectional view with placed collagenous drug carrier loaded with gentamycin underneath, above, and between the sternal edges and redon catheters under each pectoralis major muscle flaps and in the anterior mediastinum.

The surgical procedure included wide excision of the original skin incision, removal of all suture materials, sternal wires, and nonviable tissue. The sternum was debrided back to bleeding bone. The mediastinal tissue was carefully debrided until gentle bleeding of the tissue occurred and the wound was repeatedly flushed with 3 L of gentamycin solution (240 mg/L). After the debridement the pectoral major muscle flaps were raised bilaterally. The dissection was limited superiorly at the level of the clavicles and laterally, at the mid clavicular line. Inferiorly, the plane of dissection passes to the undersurface of the anterior rectus fascia. This allows an easy advancement of the myocutaneous flaps to the sternal midline without tension. A plastic multihole catheter (PFM, Cologne, Germany) was placed under each flap, a third catheter was placed retrosternally in the anterior mediastinum. Each redon catheter was connected to a vacuum-collecting bottle (Dahlhausen, Cologne, Germany) applying negative suction. Two to three sulmycin implants, 10 by 10 cm (Essex Pharma, Munich, Germany) containing 260 to 390 mg of gentamycin were placed underneath, above, and between the sternal edges before rewiring (Fig 1). Sternal closure was performed using 10 to 12 stainless steel wires (Charr. 6, Deknatel, Fall River, MA), four were placed through the body of the manubrium, the remaining wires were placed through the body of the sternum. If the sternum was severely osteoporotic or fractured the sternal closure was reinforced using the Robiczek sternal reinforcement technique [11]. A one-layer single suture technique with a 2.0 monofilament nonabsorbale suture (Ethicon, Norderstedt, Germany) was used to appose the pectoralis major muscles and close the skin. The myocutaneus muscular flap tubes were removed at day 2 and the mediastinal tubes at day 3 after debridement but not before sterilization of the mediastinal effusion.

Antibiotic management was started systemically before debridement with vancomycin and clindamycin, if no bacterial susceptibility test result was available before operation. Thereafter, the antibiotic regimen was adapted to the results of bacterial susceptibility testing. The antibiotics were applied intravenously for the first 3 weeks followed by oral administration for a total duration of 6 weeks [12].

Treatment failure was defined as recurrence of infection within a time span of 6 months.

	Results

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Sternal closure was performed with simple wire stitches in 24 of 42 patients (57%); the Robiczek sternal reinforcement technique was used in the remaining 18 of 42 (43%) patients.

In the susceptibility testing 8 of 52 patients (15%) had organisms that were resistant to gentamycin. The incidence of polymicrobial infections was present in 8 of 42 patients (19%).

The time interval between the open heart procedure and occurrence of infectious symptoms was 12.1 ± 4.8 days (range, 4 to 22 days). The most frequent signs of infection were leukocytosis (38 of 42 patients, 90%), sternal instability (35 of 42, 83%), drainage from the sternal wound (32 of 42, 76%), and increased pain (27 of 42 patients, 64%).

The associated general morbidity after surgical debridement were prolonged ventilation (8 of 42 patients, 19%) and multiple organ failure (3 of 42 patients, 7%), which complicated the postoperative course. The mean time for sterilization of mediastinal effusions was 25.7 ± 8.6 hours. The mediastinal drainage samples were sterile in all patients before removal of the mediastinal tubes. Gentamycin plasma and wound exudate levels were determined in 19 patients (Fig 2). High bactericidal gentamycin levels, more than 300 mg/mL, were detected in the mediastinal effusions for 36 hours postoperatively, whereas the plasma levels were below 2 mg/mL in all patients.

View larger version (9K): [in this window] [in a new window]   Fig 2. Mediastinal efflusion (closed circles) and plasma (open circles) gentamycin levels up to 36 hours after surgical debridement (n = 19).

	Comment

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The optimal treatment of deep sternal wound infection is still controversial. There are two different doctrines: closed continuous irrigation techniques versus muscle flap reconstruction techniques. Closed continuous irrigation techniques resulted in high failure rates up to 36% in most reports [5–7]. Recently, Molina [13] described a modification of the irrigation suction system in closed continuous irrigation with no treatment failures up to 8 years, but only in a small number of patients (n = 16). Calvat and coworkers [14] compared closed continuous irrigation with closed drainage using redon catheters and were able to demonstrate that treatment failures and mortality rate could be reduced using redon catheters applying negative suction for closed drainage. They hypothesized that strong negative suction is superior to continuous irrigation in removing infected serous fluids. However, mortality (17%) and failure rate (13%) were still substantial in this series.

Muscle flap procedures are increasing the local circulation in the infected area and filling the dead space between the dehisced sternum, improving outcome after deep sternal wound infection. However, reinfection and sternal instability remains a major problem [3, 8, 9]. Surgical techniques dealing with deep sternal wound infections should always follow the principles of septic surgery, such as removal of infected tissue and material, immobilization and improvement of local circulation. These principles are fulfilled by wide excision of all nonviable and infected tissue, removal of foreign material, and sternal bone debridement as well as mediastinal debridement, combined with thorough wound irrigation, sternal rewiring for stabilization, pectoralis major myocutaneous flaps to improve local circulation, and closed drainage with retrosternal redon catheters applying negative suction to remove potential infected mediastinal exudate. Even under ideal circumstances is it not always possible to remove all infected tissue surgically, which would result in failure of the initial treatment and necessitate a more aggressive and disabling surgical redebridement to treat the primary failure. According to Culliford and coworkers [15] sternal osteomyelitis is decisive for the development or maintenance of deep sternal wound infection. Therefore, persisting sternal osteomyelitis could be a reason for treatment failure after surgical debridement. Von Hasselbach [10] showed that the adjuvant treatment with collagenous gentamycin resulted in high local bactericidal concentrations, up to 2,500 mg/L without systemic toxic levels in patients suffering from osteitis. Gentamycin levels derived from mediastinal effusions in our patients were more than 300 mg/L for 36 hours, whereas the plasma levels were well below the systemic toxic threshold (> 10 mg/L) (Fig 2). Therefore, a high bactericidal concentration of gentamycin in the anterior mediastinum and sternal bone can be anticipated. The bactericidal effect of aminoglycosides is dependent on the peak level, and a high peak level is associated with a high bactericidal effect [16, 17].

The minimal inhibitory concentration of gentamycin for systemic antibiotic therapy in the bacterial susceptibility testing is 4 mg/L. However, resistance is not an absolute feature of bacteria, but it results from the relation of growth inhibitory concentration of the bacteria to inhibitory concentration in the tissue. Grimm [18] demonstrated that resistant bacteria at the minimal inhibitory concentration level are sensitive to higher gentamycin levels. In the present study the peak levels of gentamycin were 75 to 200 times higher than the minimal inhibitory concentration. Therefore, those high peak levels may be bactericidal for even those pathogens that are resistant according to present laboratory testing (minimal inhibitory concentration of 4 mg/L). Furthermore, the chemotactic effects of the collagenous structure proteins, together with the guiding function for connecting tissue migrating in the wound, may possibly accelerate the healing process [19, 20]. Thus, each component of collagenous gentamycin may be effective, whereby gentamycin acts as a bactericidal agent and the carrier substance collagen possibly supports the wound healing process and bone regeneration.

Surgical wound debridement, bilateral pectoralis major muscle flaps, retrosternal redon catheters, sternal rewiring, and the adjuvant therapy with topical collagenous gentamycin as a new therapeutic policy lead to excellent results in the treatment of early deep sternal wound infections with no death and no primary treatment failures. The preliminary results are encouraging; however, our data are tentative and should serve as a basis for more definitive future studies. For final judgment of this technique, a prospective randomized trial is mandatory.

	References

Top Abstract Introduction Material and methods Results Comment References

 

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