The retrospective study was approved by the hospital ethics committee and informed consent of patients. From January 2018 to December 2019, 12 patients with DSWI following cardiac surgery underwent ALBC and VSD treatment in the department of cardiac surgery at affiliated Wuxi People's Hospital of Nanjing Medical University. In each case, after the diagnosis of DSWI was established, the basic principle of treatment were debridement, administration of culture-specific or broad-spectrum antibiotic. The patient characteristics, pathogenic data, the mean hospital stays were retrospectively analyzed(Table 1).
Definitions of DSWI
As defined by the Centers for Disease Control and Prevention, DSWI diagnosis requires at least one of the following criteria: (I) an organism is isolated from culture of mediastinal tissue or fluid; (II) evidence of mediastinitis seen during surgery; (III) one of the following conditions: chest pain, sternal instability, or fever (>38 ℃) in combination with either purulent discharge from the mediastinum or isolation of an organism from culture of blood or mediastinal drainage.
We assembled a multidisciplinary team in our department that included cardiac surgeons, chronic wound control physician, Clinical pharmacists, dietitian and nurses.
Complete debridement of the wound always took place in the operating room under general anaesthesia. A thorough mediastinal wash out was the first step of sternal reconstruction. Next, Operative debridement of infected bone and soft tissue was
used, including removal of sternal wires and other foreign bodies (e.g., sutures, pericardial patches, pacemakers). Then, normal bone tissue with a good blood supply was reached (Fig. 1b, Fig. 2b, Fig. 2c, Fig. 2d). Cultures were aslo taken from the wound to identify the causative bacteria and adjust the administered antibiotics determined by antibiogram. Next, selection of surgical procedure mainly depends on detection of sternal exposure, sternal instability, extent of sternal bone loss.
Method 1. If infected sternal with minor bone loss(Fig. 1a, Fig. 1b), the ALBC was coverd the defect of sternal to provide a reliable bone stability (Fig. 1c). The commercial cements were manufactured with antibiotics premixed, hand-mixed preparations were still commonplace. The amount of gentamycin in this commercial cements (PALACOS MVⓇ+G bone cement，Heraeus, Heraeus Medical GmbH, Wehrheim, Germany) is 0.55 g. The antibiotic loaded cement is prepared by combining a 40 g bag of cement with 2 g of vancomycin or 3.2g gentamicin powder. The polymerization of bone cement increases the temperature of the cement mixture to 60℃-80℃. Therefore, it is necessary to rinse the wound with saline to reduce the local temperature. Also, the holes were made on the surface of ALBC for drainage(Fig. 1c). VSD (Wu han VSD Medical Science & Technology Co., Ltd. Vacuum Sealing Drainage Dressing) coverage was provided for the ALBC (Fig. 1d). It was removed when output was less than 5 ml/day for 3 days. When inflammatory markers include white blood cell, ESR, CRP level were normal for a week, the second re-exploration revealed a clean, red, granulating wound bed was achieved(Fig. 1e, Fig. 1f). Two drain tubes(Disposable negative pressure drainage pipeline, AY-Y18-Q400, Ai yuan medical technology, Jiangsu, China) were placed under the subcutaneous layer. The subcutaneous tissues were intermittently sutured (Fig. 1g). Seven weeks later, the wound looked healthy and showed no evidence of dehiscence or infection(Fig. 1h).
Method 2. If infected sternal with major bone loss(Fig. 2a), pectoral muscle and subcutaneous tissue were mobilized from the chest wall(Fig. 2e). The ALBC was placed in between both sternal halves and coverd the defect of sternal to fix the thorax(Fig. 2f). The treatment method of bone cement was the same as method 1. Two drain tubes were placed: one under the muscle flap and the others under the subcutaneous layer. The skin was relaxedly sutured without significant tension(Fig. 2g). Finally, VSD coverage was provided for the wound (Fig. 2h). Connected to the vacuum device, the negative pressure is -75 mmHg to -100 mmHg. It was removed after intermittent use for about 1 week.
The perioperative management included: maintenance of hemodynamic stability, nutritional support, surveillance and control of perioperative glycemia (<200 mg/dL), perioperative antibiotic choice, minimization of blood product usage, postoperative wound care, and patient education regarding prevention of incisional infection.
Measurements of pulmonary function (n = 12) using volume displacement body plethysmography were carried out by comparing the results to preoperative reference value.
Blood/Local concentration of vancomycin test
The blood concentration of vancomycin (n = 9) was assayed at postoperative day 1, day 3, day 5, day 7, day 9, day 11, day 14 and local concentration was assayed at postoperative day 1, day 3, day 5, day 7.
Continuous variables were expressed as mean ± standard deviation. A paired t-test was performed to evaluate the changes in pulmonary function values. A P-value below 0.05 was considered statistically significant.