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Eur J Cardiothorac Surg 2002;22:271-277
© 2002 Elsevier Science NL
Department of Thoracic and Cardiovascular Surgery, Rikshospitalet, N-0027 Oslo, Norway
Received 16 January 2002; received in revised form 19 April 2002; accepted 22 April 2002.
* Corresponding author
e-mail: ivar.risnes{at}rikshospitalet.no
| Abstract |
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Key Words: Sternal wound infection Wound closure Surgical zipper
| 1. Introduction |
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The etiology of sternal infections following cardiac surgery is multifactorial, and implicates many risk factors [15]. Most pathogens, whether endogenously or exogenously acquired, are believed to be implanted at the time of surgery [6,7]. A recent study from our department comparing intracutaneous versus transcutaneous suture technique indicates that the wound closure technique may represent an important risk factor for postoperative sternal infection after cardiac surgery [1]. The incidence of superficial wound infection was significantly increased with the intracutaneous technique compared with the percutaneous method. The cosmetic result was equal for the two techniques.
Traditional suture closure may create tension across the width of the wound contributing to inadequate circulation [8,9]. Moreover, bacterial adhesion to surgical sutures represents an important factor in the development of postoperative wound infection [10,11].
The goal of wound healing is to prevent wound infection, and to achieve a good cosmetic result. The non-invasive surgical zipper closure may contribute to the natural healing process of the wound by a homogeneous distribution of tension across the entire wound area. In this prospective randomized study we wanted to investigate the advantages and disadvantages of the Medizip Surgical Zipper versus intracutaneous skin closure in patients undergoing open-heart surgery.
| 2. Methods |
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Patients undergoing elective or emergency cardiac surgery with sternotomy and cardio-pulmonary bypass (CPB) were included in the study. The only exclusion criteria were immunosuppressive or steroid medications prior to surgery.
All patients who developed mediastinitis underwent re-exploration with debridement, sternal closure ad modem Robicsek [12], and mediastinal irrigation with antibiotic solution and systemic antibiotic therapy.
The study was approved by the regional ethics committee.
2.2. Surgical technique
Anaesthesia was induced with diazepam, fentanyl and pancuronium and maintained with fentanyl, midazolam, isoflurane (Alpharma, Oslo, Norway) and nitrous oxide.
In all patients the operative approach was through a median sternotomy, with cardio-pulmonary bypass and moderate systemic hypothermia. Thirty-two patients were operated in deep hypothermia and circulatory arrest. Cold crystalloid cardioplegia and topical cooling with ice slush were used routinely. All CPB circuits were heparin-coated with Baxter Duraflo II, including the Spiral Gold Oxygenator, (Baxter Health-Care Inc., Irvine, CA). The initial heparin dose was 4 mg/kg to achieve an ACT>480 s. After CBP was terminated, protamine sulfate 10 mg/ml (Leo, Løvens Kemiske Fabrik, Copenhagen, Denmark) was administered to re-establish preoperative ACT level. Mediastinal shed blood was retransfused. The amount of heparin and protamine, the ACT values, the mediastinal blood loss, and the retransfused blood volumes during the first 12 postoperative hours were recorded in all patients.
2.3. Data collection and analysis
Data were obtained from our surgical database, and by review of the patients charts, including the following preoperative risk factors: age, gender, underlying disease, preoperative functional class (New York Heart Association (NYHA) classification), cardiac index, chronic obstructive pulmonary disease, redo surgery, preoperative serum creatinine, endocarditis, emergency surgery and previous myocardial infarction (Table 1). Operative risk factors included operative procedure, duration of anaesthesia and CPB, aortic cross-clamp time and emergency vs. elective surgery. Postoperative factors included duration of mechanical ventilation, number of blood transfusions, re-exploration for bleeding, mediastinal drainage and length of hospital stay.
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Medizip is a combination of hypoallergenic, microporous polyester, coated with acrylate adhesive and a zipper, and is economically not more than 50% higher, and needs no bandage, compared with ordinary intracutaneous suture (Fig. 1) . The economical considerations will probably not prohibit the appliance of the zipper in routine cardiac surgery. The skin was cleaned with alcohol, and the wound elongated manually to approximate the wound edges. The zipper was routinely not opened until removal after 12 days.
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The sternal wound was inspected after 6 weeks by the patients themselves. All patients were informed about the study and the infection signs, and all wanted to take part. Assessment of wound infection was made according to the specific classification scheme as previously suggested by Andenaes et al. [1315]. Each wound was given a score from 0 to 7 with zero representing the optimal, physiologic postoperative wound appearance. The superficial wound infection (SWI) was defined as a score of 4 or more, that means postoperative wound conditions with pus combined with other signs or symptoms [1315]. Deep wound infection (DWI) included acute mediastinitis with sternal dehiscence and osteomyelitis of the sternum. The patients themselves graded the wound, and defined if infection had appeared or not. At the same time they cosmetically evaluated the wounds, using a visual scale from 1 to 10, with 10 representing the best.
2.5. Baseline blood samples
Haemoglobin, leukocytes, C-reactive protein and S-creatinine were determined preoperatively, and on the 1st, 2nd and 3rd day postoperatively.
2.6. Statistical methods
We estimated the crude effect of the two techniques of wound closure on different endpoints by odds ratio and 95% confidence interval using the MannWhitney U-test and Fisher's exact test.
The major endpoints were the total number of infected patients (SWI and DWI), SWI and DWI.
To adjust for possible risk factors, we used the multivariate logistic model to estimate the efficacy of the two treatments when controlling for the major risk factor [16,17].
The univariate analysis was performed using Epi-6 [18], and the multivariate analysis with BMDP [19].
| 3. Results |
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One patient developed mediastinitis on the second postoperative day. In the other patients signs of clinical infection presented later than the third postoperative day, and none of the zippers were opened during the hospital stay. The incidence of total infection after 6 weeks was equal in the two groups (6.7 vs. 6.7%), which gives an odds ratio of 1.0 (95% confidence interval (CI) 0.372.69) (P=1.0). The risk of superficial wound infection in the MZ group was 5.3 vs. 6.0 in the IC group, which gives an odds ratio of 0.88 (95% CI 0.302.58) (P=0.80). The incidence of mediastinitis in the IC group was 0.7% compared with 1.4% in the MZ group, odds ratio 2.01 (95% CI 0.145.60) (P=0.56) (Table 2).
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3.4. Microorganisms
Among the 20 infected patients the causative organism was Gram-positive bacteria Staphylococcus aureus which was found in 50% of the patients. In one patient, Candida albicans was found, while in four patients there was no growth. In another five infected patients no bacterial tests were performed.
3.5. Cosmetic results
The patients were satisfied with the cosmetic results. On a cosmetic scale from 1 to 10, an average score of 8.2 (±1.6 SD) was obtained in the IC group versus 8.9 (±1.5) in the MZ group (P<0.01).
| 4. Discussion |
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In the present trial the infection rate was equal for the intracutaneous group compared with the MZ group, based on the patients own assessment. However, the cosmetic result of the scars was significantly better for the zipper. As most patients are transferred to their local hospitals on the third postoperative day, and the clinical signs of infection occur after day 3, we assume that the problem of sternal wound infection may often be underestimated. Andenaes has previously demonstrated that the patient's assessment of the wound is as good as the doctor's assessment [15]. The patients were told that the zipper method represents a new method to be tested. The possibility for placebo effect is present as the patient may expect the zipper to leave a better cosmetic result and less infection. However, this method excludes the possibility of bias by the blinded investigators. An assessment by a third party was not possible for practical reasons, as all patients referred to Rikshospitalet come from the entire country. In order to include a high number of patients, asking the patient to fill in a standardized questionnaire covered routine control assessment of the wound.
Prior to this study we estimated the total incidence of infection in our patient group to be around 11%. After moving to a new hospital building in June 2000, the average incidence of infections dropped from 11 to 6.7%. This drop created a certain power deficiency in our study.
Mechanical forces acting across the width of wounds may contribute to the formation of scars that are functionally or cosmetically unsatisfactory [7]. Tissue trauma also represents a certain risk of wound infection that can be further increased by the various application techniques using sutures and staples [8,9]. Bacterial adhesion to foreign suture material may represent a factor in the development of postoperative wound infection [20].
When tissue is injured, a typical sequential vascular response to injury occurs. After the initial vasodilatation, the damaged vessels may occlude to thrombosis, and the larger muscular vessels contract. An inadequate circulation limits the healing [7,20,21].
The present study compared a non-invasive surgical zipper to intracutaneous suture skin closure. Poliglecaprone intracutaneous suture was applied superficially in the dermis. This might promote the access of superficial bacteria into the underlying suture and tissue, where adhesions, interfilament spread and protection from phagocytosis might provide an easier development of infection. The overall limit of oxygen present in a healing wound is very important for postoperative wound infection, as decomposition of absorbable sutures necessarily needs oxygen additionally to the requirements for healing process. The relation between ischaemic tissue after surgery, protection from phagocytosis and easier survival of bacteria are of critical importance to wound healing and to the susceptibility of infection [7,20,21]. The most important requirements for good scar result are primary wound healing without tension and lack of trauma to the wound edges [22,23]. The Medizip Surgical Zipper provides a homogeneous distribution of stress (tensile forces and shearing forces) across the entire wound region, and causes less oedema than the intracutaneous sutures [23,24]. The patient's own skin is considered to represent the main source of pathogenic bacteria. The main routes of entry of these organisms are via the surgical incision at the time of operation and sutures for wound closure [6,20].
In our study Monocryl 3-0 IC was used intracutaneously. Bacterial adhesion to surgical sutures is an important factor in the development of postoperative wound infection. Low virulent bacteria, e.g. Staphylococcus epidermidis, are highly adhesive to biomaterials in general [20].
With Medizip, the risk of invasion from skin pathogens is considered to be reduced. Many of these objectives are overcome because there is no perforation of potentially infected structures in the skin, no foreign body reaction to facilitate bacterial invasion and no tension in the wound area [2025].
Considerations when choosing an appropriate suture for wound closure and healing should include strength of suture, holding power of tissue, bacterial adherence to surgical sutures and risk of infection. Based on these methods the zipper closing system was expected to be a safe alternative to conventional suture material. Wound edge approximation is even and enables an undisturbed healing progress. The surgical demands of a wound free of tension are met to a considerable extent by the lack of trauma to the wound edges [25]. However, introduction of a new material and a new procedure may be associated with initial handling problems.
The edges of the wound have to approximate without leaving any gaps or overlapping. This is not always the case, and may represent a certain risk of wound infection and varying cosmetic results. In a few patients the zipper was opened, and wound inspection was done. We saw a small step formation at the edges in the wound area in many patients, and a dead space of blood collection between the zipper and the skin. The zipper is a non-invasive closing system, but may potentate wound infection when necrotic or devascularized tissue, haematoma or dead space caused by tissue damage or poor surgical technique are present. When applying the Medizip it is important that a distance of 0.5 cm is maintained between the zipper teeth and the edge of the wound, and that there is an adequate subcutaneous suturing with good haemostasis.
Opening the zipper is noticeably difficult, and may disturb the wound-healing progress. The adhesive strength of the zipper is good. Once glued to the skin in the operation room it remains securely in place, and removing too early can disturb wound healing. Skin reactions or allergic reactions were observed neither by the staff nor the patients (see Fig. 2) .
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In summary, our analysis indicates that the cosmetic result is better with the non-invasive zipper technique compared with the intracutaneous method. The incidence of total infection was equal for the two techniques. In order to obtain a better cosmetic result, the zipper wound-closing technique can be recommended.
| Acknowledgments |
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| References |
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