The cost of vacuum-assisted closure therapy in treatment of deep sternal wound infection

Abstract

Objectives. Surgical sites infections are very expensive and the total costs for coronary artery bypass grafting (CABG) surgery followed by deep sternal wound infection (DSWI) with conventional therapy are estimated to be 2.8 times that for normal, CABG surgery. Promising results have been reported with vacuum-assisted closure (VAC) therapy in patients with DSWI. This study presents the cost of VAC therapy in patients with DSWI after CABG surgery. Design. Thirty-eight CABG patients with DSWI, between 2001 and 2005, were treated with VAC therapy. The cost of surgery, intensive care, ward care, laboratory tests and other costs were analyzed. Results. No three-month mortality or recurrent infection was observed. The average cost of CABG procedure and treatment of DSWI was 2.5 times higher than the mean cost of CABG alone. No significant correlations were found between the preoperative EuroSCORE and the cost of DSWI therapy. Conclusions. VAC therapy for patients who underwent CABG surgery followed by DSWI seems to be cost effective, and has low mortality rate.

• Health economics
• health policy
• mediastinitis
• wound closure
• CABG
• sternum

Deep sternal wound infection (DSWI) is a devastating complication following cardiac surgery and is associated with significant increases in hospital length of stay, hospitalization costs, morbidity and mortality 1. Previous studies have reported infection rates from 0.5 to 3.2% 2–8, and mortality rates varying between 7 and 36% with conventional therapy 2–9. Conventional forms of treatment involve surgical revision with open packing dressing, rewiring over an irrigation catheter, or reconstruction with vascularized soft tissue flaps, such as omentum or pectoral muscle. Previously, several studies have reported promising results using vacuum–assisted closure (VAC) therapy in patients with DSWI after cardiac surgery 10–15. In these patients, the VAC therapy has been successful, either as a single-line therapy 16 or as a procedure for providing optimal conditions for second-line treatment with tissue flaps 17. We have used VAC as a single-line therapy followed by sternal rewiring without the use of tissue flaps.

Surgical sites infections are very expensive for health care providers and the total costs for coronary artery bypass grafting surgery (CABG) followed by DSWI with conventional therapy are estimated to be 2.8 times that for normal, CABG surgery 4. To the best of our knowledge, no study has yet described the economic impact of VAC treatment of patients with DSWI. The aim of the present study was to calculate the cost of VAC therapy in patients with DSWI after CABG surgery. Furthermore, we also evaluated EuroSCORE as a predictor for high cost in patients with DSWI.

Materials and methods

Between January 2001 and January 2005, 4985 patients underwent open heart surgery at the department of cardiothoracic surgery, Lund University Hospital, Lund, Sweden. During this period, 3675 CABG procedures were performed with a DSWI rate of 1% (38/3675). The follow-up was performed in December 2005. Information about the patients was collected from the computerized database at our department and, when needed, from the patients’ medical records. Ethics Committee at Lund University, Sweden, approved the research protocol for this study.

Thirty-eight consecutive patients, undergoing CABG, were treated for culture-verified DSWI. Fifteen patients presented DSWI before being discharged. The mean period from initial operation until diagnosis of DSWI in those patients was 10 days±0.7 (range 6 to 16).

Twenty-three patients presented DSWI after they had been discharged from hospital. They were readmitted for treatment. These patients developed DSWI after a mean period of 17 days±1.2 (range 8 to 30). The Department of Cardiothoracic Surgery, Lund University Hospital, Lund, Sweden is the only cardiothoracic surgery unit in the southwest region of Sweden and all patients suffering from DSWI were readmitted to our department. Preoperative, perioperative, and postoperative data, including the EuroSCORE (the European System for Cardiac Operative Risk Evaluation) 18 were collected, for each patient (Table I). The EuroSCORE was used to assess the degree of surgical complexity and preoperative status. In addition, information on risk factors considered relevant to developing DSWI, such as diabetes mellitus and obesity was collected from the patients’ medical records 19.

Table I.  Pre- and perioperative variables.

	DSWI-patients
Variable	n (38)	%
Age^a	69.0±10.6
Female gender	9	23.6
Diabetes mellitus	15	39.4
Obesity (BMI >30)	10	26.3
COPD	9	23.6
Recent MI (<90 days)	16	42.1
LVEF <30%	7	18.4
Renal failure^b	3	7.8
Critical preoperative status	3	7.8
Emergency surgery	6	15.7
Three-vessel disease	33	86.8
Re-exploration (bleeding)	3	7.8
EuroSCORE^a	6.1±3.5

Patients who presented DSWI during postoperative care.

DSWI = deep sternal wound infections; ^aMean±standard deviation; ^bSerum creatinine >200 µmol/L (2.27mg/dL); BMI = body mass index, kg/m²; COPD = chronic obstructive pulmonary disease; LVEF = left ventricular ejection fraction; MI = myocardial infarction.

The criteria used for the definition and classification of DSWI were those specified in the guidelines of the US Centers for Disease Control and Prevention 20. Diagnosis of mediastinitis required at least one of the following criteria:

1. an organism was isolated from a culture of mediastinal tissue fluid;

2. evidence of mediastinitis was seen during operation; or

3. one of the following conditions: chest pain, sternal instability or fever (>38°C) and there was either a purulent discharge from the mediastinum or an organism was isolated from blood culture or culture drainage of the mediastinal area. Patients with sterile dehiscence or superficial sternal wound infections were not included.

Medical therapy

Our standard perioperative antibiotic regime is 2 g isoxazolyl penicillin, three doses on the day of operation and on the first postoperative day. Patients with a history of allergic reaction to penicillin were given 600 mg klindamycin instead. When DSWI was diagnosed, the antibiotic therapy usually commenced with vancomycin and imipenem intravenously and continued until the results of the tissue cultures became available. Thereafter, the antibiotic therapy was adjusted according to bacterial sensitivity and strain. The entire panorama of pathogens is presented in Table II.

Table II.  Culture-verified mediastinal pathogens.

	DSWI-patients
Bacterial strain	n (38)	%
CoNS	18	47
Staphylococcus aureus	5	13
Enterobacter cloacae	3	8
Klebsiella oxytoca	2	5
Propionibacterium acnes	2	5
CoNS + Staphylococcus aureus	2	5
CoNS + Propionibacterium acnes	3	8
CoNS + Proteus mirabilis	1	3
CoNS + Pseudomonas aeruginosa	1	3
Klebsiella pneumoniae+Propionibacterium acnes	1	3

DSWI = deep sternal wound infection; CoNS = coagulase-negative staphylococci strains.

Vacuum-assisted closure therapy

Thirty-eight patients who had undergone CABG and developed DSWI were given single-line VAC therapy followed by sternal rewiring without the use of soft tissue flaps.

Foreign material such as steel wires and sutures were debrided. Five tissue cultures were obtained from different substernal sites of the wound. Debridement of clearly necrotic and infected soft tissue was performed at once but no deep revision was made around the heart. Sternal edges were revised with a sharp spoon. Special attention was directed to the left hemisternum and underlying right ventricle by checking for adherences and sharp edges. That was followed by saline irrigation and thorough hemostasis. Three or four layers of paraffin gauze dressing were placed at the bottom of the wound covering and isolating visible parts of the right ventricle, lung tissue, and grafts from the sternal edges. Sterile polyurethane foam dressing, (KCI, Copenhagen, Denmark) was trimmed to fit between the sternal edges. It was cut as a strip, 1.5 times broader than the sternal diastase to allow volume reduction when the vacuum was applied. This layer was used to seal the gap between the bone edges and was not placed below the level of the sternum. The second layer of polyurethane foam was placed subcutaneously, covering the wound completely. This layer was then secured subcutaneously with a running suture (Dermalon 2-0) to the surrounding skin edge. A skin barrier protector (Cavilon; 3M HealthCare, St. Paul, MN) was applied and the open wound was sealed with a transparent adhesive drape (KCI, Copenhagen, Denmark). The drape overlapped the wound margins by 5 cm to avoid air leakage. The drainage tube from the closed wound were connected to a purpose-built vacuum source (VAC pump unit; KCI, Copenhagen, Denmark). The pump unit was programmed to deliver -125 mm Hg continuous negative pressure A canister in the pump unit collects exudates from the wound. The polyurethane foam and layers of paraffin gauze dressing were changed two to three times a week under aseptic conditions and general anaesthesia 16.

Data analysis

The cost analysis proceeded from the perspective of the health-care provider. Cost data were derived from the computerized internal cost accounting database for our hospital. The actual costs of surgery, intensive care, ward care, laboratory tests and other costs were calculated. All costs are presented in US dollars at the time of follow-up. The mean exchange rate for 2005 was 1 US dollar ($) = 7.47 Swedish krona (SEK)1. Calculations and statistical analysis were performed using the Intercooled Stata version 9.0 (2005) statistical package (StataCorp LP, College Station, Texas), and graphs drawn using Microsoft Excel 2003 (Microsoft Corporation, Redmond, WA). Values are presented as mean±SEM. Univariate linear regression analysis was used to test the correlation between the EuroSCORE and cost ratio. A p value less than or equal to 0.05 was considered statistically significant.

Results

No three-month mortality or recurrent infection was observed. The mean cost of CABG alone was $17 574 and can be broken down as demonstrated in Figure 1. The mean cost of treating DSWI was $26 670: ward care (37.5%), surgical costs (25.1%), ICU care (24.9%), laboratory tests (4.5%) and other costs (9.9%) (Figure 2).

Figure 1.  Total cost of CABG, and the cost of ward care, ICU care, surgery, laboratory tests and other costs. (Mean±SEM). CABG = Coronary Artery Bypass Grafting, ICU = Intensive Care Unit, USD = United States Dollars,

Figure 2.  Total cost of DSWI treatment, and costs of ward care, ICU care, surgery, laboratory tests and other costs. (Mean±SEM). DSWI = Deep Sternal Wound Infection, ICU = Intensive Care Unit, USD = United States Dollars,

The average cost of CABG procedure and treatment of DSWI was 2.5 times higher than the mean cost of CABG alone. The total cost of CABG followed by DSWI treatment in patients who had been discharged from hospital and readmitted due to DSWI is made up as follows: surgery 32.1%, ward care 31.6%, ICU care 24.4%, laboratory tests 4.6% and other costs 8.3%. In 52% of the patients who had been discharged and readmitted due to poststernotomy mediastinitis the cost of DSWI therapy alone was less than the mean cost of CABG alone. For 22% of the patients, the total cost of DSWI treatment was up to two times higher than the mean cost of CABG. In 13%, the total cost was up to three times higher than the mean cost of CABG, and in 13% of the patients three to five times higher. No significant correlation was found between a high EuroSCORE and high cost of treating of DSWI (Figure 3).

Figure 3.  Mean cost of CABG surgery and DSWI treatment divided by the mean cost of CABG surgery (cost ratio), (y-axis) in each EuroSCORE risk group (x-axis). No significant correlation was seen between the cost ratio and EuroSCORE, (p=0.593). DSWI = Deep Sternal Wound Infection

Discussion

VAC therapy has become an established form of treatment in patients with DSWI. The surgical technique has been well described 11–17. Furthermore, patients undergoing VAC therapy for DSWI following CABG surgery demonstrate no significant increase in mortality up to four years after surgery compared to CABG patients who have not suffered DSWI 21.

We calculated the cost ratio between the total cost of DSWI treatment plus CABG surgery and the mean cost of CABG surgery for those patients who were readmitted due to DSWI. We found that the mean cost of CABG alone on a patient at Lund University Hospital, Lund, Sweden, was $17 574 (Figure 1) and the actual cost for CABG followed by DSWI was, on average, 2.5 times higher than that of CABG procedure without DSWI.

Loop et al. 4, at the Cleveland Clinic Foundation, Cleveland, Ohio, treated their patients who underwent CABG surgery followed by DSWI with conventional forms of treatment involving surgical revision with open packing dressing, rewiring over irrigation catheter, or reconstruction with vascularized soft tissue flaps such as omentum or pectoral muscle. They reported that the total cost of treating patients with CABG followed by DSWI was 2.8 times higher than the cost of CABG procedure without DSWI. In their study, 14% of the patients died due to multiorgan failure. In a study by Hollenbeak et al. 1 at the Department of Surgery, Pennsylvania State College of Medicine, Pennsylvania, a cost ratio of 2.5 was reported for patients with DSWI. They also used conventional therapy for DSWI and experienced a mortality rate of 22%. They reported a cost of $20 012 for uncomplicated DSWI. They found that CABG patients who developed DSWI and subsequently died cost approximately $60 546 more than infected patients who survived. If conventional therapy for DSWI fails, the patient will become critically ill, exhibiting sepsis and multiorgan failure, which will increase the cost of care dramatically.

All patients in the present study were treated with single-line VAC therapy followed by rewiring and closure without the use of soft tissue flaps. Neither three-month mortality nor recurrent infection was observed. This study demonstrates that in 52% of the patients who were readmitted due to DSWI, the total cost of VAC treatment only was less than the mean cost of CABG only. However, in 13% of the patients the cost of care for DSWI was three to five times higher than that of the CABG procedure. These last cases probably reflect the patients that would have died following conventional treatment, but now survived, although at a high cost. We also studied whether the preoperative EuroSCORE was a predictor for higher DSWI costs but found no significant correlation (Figure 3).

The present study provides marked contrast regarding hospital mortality rate to earlier work presented by Loop et al. 4, and Hollenbeak et al. 1 in this patient population.

Based on the results of this study, the actual cost for CABG surgery followed by DSWI was, on average, 2.5 times higher than that of CABG procedure without DSWI and has low mortality rate. No correlations were found between the preoperative EuroSCORE and the cost of DSWI therapy after CABG surgery.

Acknowledgements

We would like to thank Elham Tizno, the economist at the Heart and Lung Center, Lund University Hospital, Lund, Sweden for her expert contributions. This study was supported by research grants from the Region Skåne Research Funds, the Swedish Heart-Lung Foundation, the Swedish Medical Association, the Swedish Government Grant for Clinical Research, and the Donation Funds of Lund University Hospital.

Notes

¹Yearly average 2005, from the Swedish Central Bank (Riksbanken) calculations of the monthly and annual averages of the Stockholm Stocks Exchange (Stockholmsbörsen's) fixes for the most common currencies. Available at URLhttp://www.riksbank.se/templates/stat.aspx?id=16748