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Interact CardioVasc Thorac Surg 2006;5:145-148. doi:10.1510/icvts.2005.122804
© 2006 European Association of Cardio-Thoracic Surgery
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Institutional report - Cardiac general

A conclusion from the first 125 patients treated with the vacuum assisted closure system for postoperative sternal wound infection{star}

Tatjana Flecka,*, Reinhard Moidlb, Pietro Giovanolic, Oscar Aszmannc, Anna Bartunekd, Alexander Blackye, Martin Grabenwogerb and Ernst Wolnera

a Department of Cardiothoracic Surgery, Medical University of Vienna, Leitstelle 20A, AKH Vienna, Währinger Gürtel 18–20, 1090 Vienna, Austria
b Department of Cardiothoracic and Vascular Surgery, Hospital Hietzing, Vienna, Austria
c Department of Plastic and Reconstructive Surgery, Medical University of Vienna, AKH Vienna, Austria
d Department of Cardiothoracic and Vascular Anesthesia, Medical University of Vienna, AKH Vienna, Austria
e Department of Infection surveillance, Medical University of Vienna, AKH Vienna, Austria

Received 25 October 2005; received in revised form 22 December 2005; accepted 23 December 2005

{star} Presented at the joint 19th Annual Meeting of the European Association for Cardio-thoracic Surgery and the 13th Annual Meeting of the European Society of Thoracic Surgeons, Barcelona, Spain, September 25–28, 2005.

*Corresponding author. Tel.: +431404005620; fax: +431404005640.

E-mail address: tatjana.fleck{at}meduniwien.ac.at (T. Fleck).


   Abstract
Top
 Abstract
1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
 References
 
Consensus exists that early recognition of sternal wound infection is crucial to prevent involvement and destruction of the sternal bone, which prohibits secondary sternal closure and necessitates the use of muscle flaps for wound closure. Since November 2001 to September 2005, 125 patients received a VAC system after surgical debridement. Thirty-eight patients had a superficial infection (2A) and 87 patients had a deep infection (2B). From those, 59 patients underwent secondary sternal closure after VAC therapy, whereas 28 patients needed muscle flap closure. The time of diagnosis of sternal infection had great impact on the outcome. It was made on POD 10.6±8.3 in the 2A group, and on POD 13.2±11.1 in the 2B group. In the patients from Group 2A who had a recurrence of infection, the initial diagnosis of infection was made on POD 13.1±11.1. In patients where an SC was possible the time of diagnosis was on POD 11.1±6.6 whereas POD 17.7±16.2 in the MF group. The key to successful management of sternal wound infection is early recognition and aggressive treatment with reopening of the entire wound and sternum, which seems mandatory to achieve a low recurrence rate.

Key Words: Sternal wound infection; Vacuum assisted closure; Secondary closure; Recurrence of infection


   1. Introduction
Top
 Abstract
 1. Introduction
2. Material and methods
 3. Results
 4. Discussion
 References
 
Sternal wound infections after cardiac surgery are a rare but serious complication, associated with considerable costs and morbidity.

The incidence is reported to be between 1% and 3% in the contemporary literature, a number which has not changed during the last 30 years, as the patient population got increasingly older with multiple risk factors [1–3].

There are several therapy options currently available, namely surgical debridement with closed irrigation or open packing and primary or secondary closure with or without muscle flaps or omentum flap. What they all have in common is the lack of consensus of using them as a single line therapy or a combination of these procedures [4–6].

With the introduction of the vacuum assisted closure system (VAC) by Argenta et al. in 1997 a new and promising treatment modality became increasingly used worldwide [7–13]. The mechanism of the VAC is based on applying controlled suction to the wound surface, thereby increasing local blood perfusion, accelerating granulation tissue formation, decreasing bacterial colonization and reducing tissue edema [7,8].


   2. Material and methods
Top
 Abstract
 1. Introduction
 2. Material and methods
3. Results
 4. Discussion
 References
 
2.1. Patient cohort

Since November 2001 until September 2005 a total of 4600 cardiac surgical procedures were performed at our department. From those, 125 patients (2.7% incidence) with a mean age of 65.5±16.3 (13 to 84 years) and a female to male ratio of 49:76 with sternal wound infection after cardiac surgery procedures received a VAC system after surgical debridement. The preceding operation was coronary artery bypass surgery in 83 patients (57%), valve repair or replacement in 45 patients (32%), ascending aortic replacement in 5 patients (4%), cardiac transplantation in 7 patients (5%) and other procedures in 3 patients (2%). Twenty-six patients (20.8%) underwent a combined procedure.

Pre-existing comorbidities were similar in both groups and were comparable with a standard Caucasian population requiring adult heart surgery (mean Euroscore of 6 points, 0 to 19 points) (Table 1).


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  		Table 1 Comorbidities and risk factors n=125

 
A total of 12 patients (9.6%) had a history of prior cardiac surgery procedures. Operating times, as well as cardiopulmonary bypass times and aortic cross clamp times were comparable to our patient population which did not develop a sternal wound complication.

Routine antibiotic prophylaxis consisted of a Cephalosporin (Cefazoline) 30 min before skin incision and 4 h and 8 h thereafter.

By the time of initial diagnosis or the suspicion of sternal wound infection, bacteriological cultures of wound secretions were routinely taken from all patients.

Post sternotomy mediastinitis was defined according to the guidelines of the US Centre for Disease Control and prevention (CDC) [14]. Wound classification was defined according to the suggestions of El Oakley and Wright [15].

2.2. Treatment protocol

All patients underwent surgical debridement under aseptic conditions in the operating theatre once sternal infection was confirmed or there was a high grade of suspicion that the origin of fever and or elevated inflammation parameters might be in the sternal wound.

After reopening of the wound and removal of sternal wires in cases of sternal instability, the mediastinum was carefully evaluated and inspected and probes for bacteriological cultures as well as sternal bone biopsies were taken. Then debridement with only removal of clearly visible necrotic tissue was performed. After the first dressing change any not removed necrotic tissue will be demarked through the VAC.

Thereafter a piece of large VAC sponge was cut and fitted between the sternal edges to prevent shear forces between the bony edges and the underlying right ventricle. Care was taken that the pericardium was properly closed to ensure no adherence to the surface of the heart. In case of incomplete pericardial adapt ion, a single layer of anon adherent open foam dressing was applied. After placing the adhesive drape in strips for better fitting, two VAC pads were installed proximal and distal and connected with the Y piece, to achieve a more uniform distribution of the vacuum and to increase thoracic cage stability. Continuous suction of 125 mmHg and of 75–100 mmHg in subcutaneous cases was installed. Sedation and prolonged respiratory support was not necessary.

Every 48 to 72 h the VAC system was changed under aseptic conditions in the operating theatre. VAC removal and definitive surgery was employed when a decline of serological inflammation parameters, negative bacteriological cultures and resolution of local infection signs in the wound were present.

2.3. Statistical methods

Statistical procedures were carried out by using SPSS 10.0 (SPSS Inc, Chicago, Illinois, USA). Data are expressed as means±S.D. Univariate analysis (ANOVA) was followed by the independent sample t-test and the Mann–Whitney U test was used as necessary for statistical evaluation of the data.


   3. Results
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
4. Discussion
 References
 
3.1. General results

A total of 125 patients sustained a sternal wound infection. From those, 38 patients developed a sternal infection restricted to the subcutaneous layer (Oakley 2A). The corresponding mean age was 58.5±16 years.

Eighty-seven patients sustained a deep sternal infection (Oakley 2B) and were on average 64±16.5 years old.

There was a trend that age corresponded with the outcome. However, this did not reach statistical significance. Whereas patients with a 2B infection, where secondary closure was possible, had a mean age of 63.1±14.8 years, the mean age of the muscle flap group was 68.8±10.1 years, P=0.047.

The isolated bacteria are displayed in Table 2.


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  		Table 2 Isolated bacteria

 
Total mortality in this cohort was 3.2% (4/125).

3.2. Infection diagnosis

The time of diagnosis of sternal infection had great impact on the outcome. It was made on postoperative day 10.6±8.3 in the superficial group, and on postoperative day 13.2±11.1 in the 2B group. In the patients from Group 2A who had a recurrence of infection, the initial diagnosis of infection was made on POD 13.1±11.1. From the patients of Group 2B we further evaluated the time of diagnosis, whether a secondary closure was feasible or a muscle flap closure necessary. In patients where an SC was possible the time of diagnosis was on POD 11.1±6.6 where-as it was POD 17.7±16.2 in the MF group (Table 3).


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  		Table 3 Patient demographics 2A vs. 2B (mean values and standard deviation)

 
3.3. VAC therapy

There was no procedure related complications and mortality in our study cohort of 125 patients and a total of 1213 VAC days.

The mean VAC duration was 9.4±3.8 days in the superficial group, 10.5±4.6 days in the 2A patients with recurrence of infection, 10.4±7.1 days in the 2B entire group, 8.9±2.8 days in the SC group and 13.3±8.2 days in the MF group (univariate P=0.01).

On average, 2.5±1.8 dressing changes were necessary until employment of definitive therapy. There were only slight differences in the 2A group with a mean number of dressing change of 2.3±1.4 vs. 3±2.4 in the 2A patients with infection recurrence. Statistically significant differences were apparent in the 2B SC group 2.2±1.1 vs. 3.6±2.8 dressing changes in the 2B MF group, P=0.3.

3.4. Outcome

The corresponding hospital stay for the 4 groups was comparable to the preceding VAC duration and as follows: 22.9±15.6 days in the superficial group, 25.6±14.7 days in the 2A recurrence group, 24.6±10.8 in the entire 2B group, 24.1±9.8 days in the SC group and 30.1±9.8 days in the MF group (P<0.001).

VAC therapy and definitive therapy was completed at our department in all patients. Patients were followed up for at least 5 days after secondary closure at our department, before discharging them home or to a rehabilitation facility.

3.5. Recurrence rate

The overall recurrence rate was acceptably low with 14 out of 125 (11.2%).

When divided into the groups however, we found a high recurrence rate in patients with 2A infection, namely 11 out of 18 (28.9%) vs. 3 out of 87 (3.4%) in the 2B group (Tables 3 and 4).


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  		Table 4 Infection types and recurrence rates

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
References
 
Historically, our management of sternal wound infections included irrigation only in subcutaneous infections and surgical debridement with immediate rewiring or muscle flap closure. However, therapy failures through infection recurrence were common [12].

In selected cases, open packing with delayed sternal closure was performed which yielded a lower recurrence rate, but the big disadvantage of conventional open packing is the destabilization of the thoracic cage through the open sternum which necessitates sedation and mechanical ventilation of the patient. This can be overcome with the VAC system as it enables full mobilization of the patient with an open sternum.

Since the implementation of VAC for the therapy of post sternotomy wound infections in Nov 2001, 125 patients have been treated with this modality with encouraging results. However, when evaluating our data, we found some deficiencies, and these need to be addressed in the future in order to maximize treatment success and to prevent infection recurrence.

4.1. Infection diagnosis

The time interval between the onset of symptoms and when treatment begins in terms of surgical intervention predicts outcome, as a delay in re-operation allows the infection to spread into the sternal bone and mediastinum, as we saw in the patients who underwent secondary closure (POD 11.1) and the patients who needed muscle flap closure (POD 17.7) [1,3].

There are several patients who have been already discharged from the hospital. Home practitioners as well as referring hospitals still do not know how to diagnose and how to treat a sternal wound infection. Referral to our department is therefore often too late, e.g. when the sternum is mobile.

Furthermore, some patients are still treated with closed irrigation or other measures which are known to be not effective until employment of VAC therapy [5,6,12].

4.2. Therapy outcome

A second cause for the failure of infection control in our series is often a consequence of insufficient debridement of subcutaneous and bony layer, which results in persistent or recurrent infection as we can see at the mean VAC duration of 9.4±3.8 days in the superficial group, 10.5± 4.6 days in the 2A patients with recurrence of infection, 10.4±7.1 days in the 2B entire group, 8.9±2.8 days in the SC group and 13.3±8.2 days in the MF group.

Radical and extensive debridement, however, has to be paid off with often large donor site defects, an unstable thoracic cage and the need of muscle flaps.

Particularly, the use of the vacuum assisted closure system can reduce the amount of debridement as it clearly demarks devitalized tissue so that an extensive safety margin is not needed.

4.3. Recurrence rate

A recent paper by Zeitani [5] evaluated the incidence and outcome of superficial wound infections. The incidence was high with 5.75% and length of treatment was mean 29.7 days, a costly and time consuming complication. In contrast to many other studies we included not only the deep sternal infections but also infections limited to the subcutaneous tissue. With VAC treatment, the hospital stay was lower (mean 22.9 days) than in the study by Zeitani, nevertheless, these infections had a high recurrence rate even with VAC therapy.

The conclusion we can draw from these average results, is that the sternum should be opened in every case, particularly in patients with a 2A infection. After evaluation we found out that the initial intention to open was as small as possible, e.g. not to open the sternum when there was no sternal instability, might be not appropriate, as an apparently stable sternum might be already seeded with bacteria and thus being a focus for an ongoing infection, which we observed in these patients. Unfortunately, 5 out of these 11 patients subsequently needed a muscle flap closure due to destruction of the sternal bone.

Moreover, it was the intention from some surgeons not to open the entire wound in cases with a localized subcutaneous infection, in order to minimize discomfort for the patients. It became apparent, however, that the bacteria were already in the whole wound and a recurrence of infection in the non-opened part was common.

We can therefore conclude, that the key to successful management of sternal wound infection is early recognition and aggressive treatment with reopening of the entire wound and sternum which seems mandatory to achieve a low recurrence rate.


   References
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
 References
 

  1. De Feo M, Renzulli A, Ismeno G, Gregorio R, Della Corte A, Utili R, Cotrufo M. Variables predicting adverse outcome in patients with deep sternal wound infection. Ann Thorac Surg 2001; 71:324–331.[Abstract/Free Full Text]
  2. Gardlund B, Bitkover CY, Vaage J. Postoperative mediastinitis in cardiac surgery-microbiology and pathogenesis. Eur J Cardiothorac Surg 2002; 21:825–830.[Abstract/Free Full Text]
  3. Jonkers D, Elenbaas T, Terporten P, Nieman F, Stobberingh E. Prevalence of 90 days postoperative wound infections after cardiac surgery. Eur J Cardiothorac Surg 2003; 23:97–102.[Abstract/Free Full Text]
  4. Immer FF, Durrer M, Mühlemann KS, Erni D, Gahl B, Carrel TP. Deep sternal wound infection after cardiac surgery: modality of treatment and outcome. Ann Thorac Surg 2005; 80:957–961.[Abstract/Free Full Text]
  5. Zeitani J, Bertoldo F, Bassano C, Penta de Peppo A, Pellegrino A, El Fakhri FM, Chiariello L. Superficial wound dehiscence after median sternotomy: surgical treatment vs. secondary wound healing. Ann Thorac Surg 2004; 77:672–675.[Abstract/Free Full Text]
  6. Douville EC, Asaph JW, Dworkin RJ, Handy JR, Canepa CS, Grunkemeier GL, Wu XY. Sternal preservation: a better way to treat most sternal wound complications after cardiac surgery. Ann Thorac Surg 2004; 78:1659–1664.[Abstract/Free Full Text]
  7. Morykwas MJ, Argenta LC, Shelton-Brown EI, McGuirt W. Vacuum assisted closure: a new method for wound control and treatment: animal studies and basic foundation. Ann Plast Surg 1997; 38:553–562.[Medline]
  8. Argenta LC, Morykwas MJ. Vacuum assisted closure. A new method for wound control and treatment: clinical experience. Ann Plast Surg 1997; 38:563–577.[Medline]
  9. Fleck TM, Moidl R, Fleck M, Koller R, Giovanoli P, Wolner E, Grabenwoger M. The vacuum assisted closure system for the treatment of deep sternal wound infections after cardiac surgery. Ann Thorac Surg 2002; 74:1596–1600.[Abstract/Free Full Text]
  10. Sjörgen J, Gustafsson R, Nilsson J, Malmsjö M, Ingenansson R. Clinical outcome after possternotomy mediastinitis: vacuum assisted closure vs. conventional treatment. Ann Thorac Surg 2005; 79:2049–2055.[Abstract/Free Full Text]
  11. Jakob HG, Borneff-Lipp M, Bach A, von Pückler S, Windeler J, Sonntag HG, Hagl S. The endogenous pathway is a major route for deep sternal wound infection. Eur J Cardiothorac Surg 2000; 17:154–160.[Abstract/Free Full Text]
  12. Fleck T, Moidl R, Koller R, Giovanoli P, Wolner E, Grabenwoger M. Delayed or primary closure for the treatment of post sternotomy wound infection. Ann Plast Surg 2004; 52:310–314.[CrossRef][Medline]
  13. Song DH, Wu LC, Lohman RF, Gottlieb LJ, Franczyk M. Vacuum assisted closure for the treatment of sternal wounds: the bridge between debridement and definitive closure. Plast Reconstr Surg 2003; 111:92–97.[CrossRef][Medline]
  14. Garner J, Jarvis WR, Emori GT, Horan TC, Hughes J. CDC definitions for nosocomial infections 1988. Am J Infect Control 1988; 16:128–140.[CrossRef][Medline]
  15. El Oakley R, Wright J. Postoperative mediastinitis: classification and management. Ann Thorac Surg 1996; 61:1030–1036.[Abstract/Free Full Text]



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