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Ann Thorac Surg 2001;71:324-331
© 2001 The Society of Thoracic Surgeons
a Institute of Cardiac Surgery, V. Monaldi Hospital, Second University of Naples, Naples, Italy
b Infectious Diseases, Institute of Medical Therapy, Gesù e Maria Hospital, Second University of Naples, Naples, Italy
Accepted for publication May 10, 2000.
Address reprint requests to Dr Renzulli, via Aquila 144, 80143, Naples, Italy
e-mail: arenzul{at}tin.it
e-mail: renzulliattilio{at}usa.net
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Abstract |
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 Top Abstract IntroductionPatients and methodsResultsCommentReferences |
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Methods. Among 13,420 patients who underwent cardiac surgery in our institution between 1979 and 1999, DSWI developed in 112 cases (0.8%). Multiple variables were recorded prospectively and analyzed retrospectively as predictors of hospital death and prolonged (>30 days) hospital stay. The analyzed variables were divided into three groups: (1) related to the patient, including demographic variables and preoperative conditions; (2) related to cardiac operation; and (3) related to infection. Predictive variables were assessed by univariate and multivariate logistic regression analysis.
Results. Hospital mortality was 16.9%. The hospital stay of the 93 discharged patients ranged between 16 and 180 days (mean 31.3 ± 15.2). Length of cardiac operation, length of stay in intensive care unit, interval between symptoms of DSWI and wound debridement were found to be the most significant predictors of bad outcome following DSWI.
Conclusions. In our study demographic variables and preoperative conditions did not affect the prognosis of DSWI. Lower mortality rate and shorter hospital stay could be achieved with earlier and aggressive treatment of DSWI.
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Introduction |
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TopAbstractIntroductionPatients and methodsResultsCommentReferences |
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The incidence of postcardiotomy mediastinal infections ranges between 0.15% [3] and 8% [4] and is approximately 1% to 2% in the most recently reported series [5–10]. Many studies [2–12] have identified risk factors for development of postoperative DSWI: many of the analyzed variables are patient-related; others are related to the surgical procedure or to postoperative clinical course. Unfortunately, only a few of these risk factors are modifiable [13]. Moreover, because of modern progresses in cardiac surgery, an increasing number of elderly and immunodepressed patients with multiple risk factors are treated surgically for cardiac diseases. Therefore, in spite of accurate hospital infection control, improved antibiotic therapy, and perioperative asepsis, the incidence of poststernotomy DSWI has remained constant over the years [4, 13].
The prognosis of DSWI is serious; despite early wound debridement, mediastinal irrigation with antiseptic or antibiotic solutions, plastic reconstruction with muscle or omental flaps, intravenous antibiotic therapy, mortality for DSWI is still high, ranging between 5% and 47% [5, 6, 10, 14]. Moreover, intensive care unit and hospital stay are significantly prolonged in patients who acquire postoperative DSWI [8, 10].
The outcome of sternal infections is often unpredictable: many patients, in spite of a slightly protracted hospital stay, achieve complete wound healing; on the contrary in other patients multiple procedures such as repetitive wound debridement, open wound dressing, plastic reconstruction procedures, local and systemic antibiotic therapy result unsuccessful, ending in hospital mortality or leading to very prolonged hospital stay with extreme distress for the patient and waste of financial resources [1, 15].
Although many authors have already investigated risk factors for development of DSWI, no studies have been performed in order to find out which variables can affect the course and outcome of DSWI. Moreover, the impact of demographic variables, preoperative conditions, and type of cardiac operation on DSWI patients’ survival has not been fully assessed yet. The purpose of the present study was to review our experience in the treatment of DSWI over a 20-year period and to assess the variables predicting hospital mortality and prolonged hospital stay.
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Patients and methods |
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TopAbstractIntroductionPatients and methodsResultsCommentReferences |
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Elective patients were showered and shaved the day of their operation. In all cases, since the morning of the operation, patients received intravenous cephalosporins and intramuscolar aminoglycosides, until central line and drains were removed.
The operative field was painted with povidone-iodine solution and the skin was covered with an adhesive plastic sheet. The skin was incised with a scalpel and electrocautery was used to open the presternal layers and the pericardium. Bone wax was used only when sternal bleeding was profuse. Internal mammary arteries (IMA), when used for coronary bypass, were harvested as pedicled in situ grafts. A chest tube was placed whenever the pleural cavity was opened. The sternum was closed with stainless steel wires. The presternal space was obliterated with two layers of adsorbable suture, and the skin was closed with a subcuticular adsorbable suture. Chest tubes were connected to 15 cm of water suction postoperatively. Patients were extubated when they were hemodynamically stable, normothermic, and ventilating spontaneously. All drains were removed on the second postoperative day or when drainage was lower than 25 mL/h. Wound dressing was removed on the second postoperative day and redressed only once. Further dressing was performed only if there was wound discharge.
Management of infection
All patients operated on at our institution were seen at 1 week, 1 month, and 6 months postoperatively in the outpatient department. Clinical status of patients breaking an appointment was assessed by phone interviews. Additional outpatient visits were prescribed when needed. Deep sternal wound infection (defined according to the guidelines of the Center for Disease Control and Prevention [16] was observed in 112 cases (0.8%). Diagnosis of DSWI required at least one of the following criteria: (1) an organism was isolated from culture of mediastinal tissue or fluid; (2) evidence of mediastinitis was seen during operation; or (3) one of the following: chest pain, sternal instability, or fever (> 38°C), was present and there was either purulent discharge from the mediastinum or an organism isolated from blood culture or culture of drainage of the mediastinal area.
As far as the demographic variables of the patients are concerned, 82 were male (73.2%) and 30 were female (26.8%) with an age ranging between 18 and 75 years (mean 58.13 ± 9.8). Nineteen patients required hospital readmission when the diagnosis of DSWI was made during their follow-up period.
As soon as the clinical diagnosis of suspected wound infection was made, swabs for culture were taken from wound secretion and sent for microbiology and patients were started on broad-spectrum antibiotic therapy.
Our policy in the treatment of mediastinitis can be divided into two periods. Until January 1995 a trial of conservative treatment was made: systemic and local antibiotic therapy together with povidone-iodine dressing was performed in all cases and the indications for surgical debridement were delayed until wound dehiscence, sternal instability, and signs of systemic infection were grossly evident. In January 1995 we changed our policy: all patients with wound discharge and even minimal sternal instability underwent wound debridement and mediastinal irrigation with povidone-iodine solution on emergency basis. Patients were taken to the operating room and wound reopening was performed. All sternal wires and fascial or subcutaneous sutures were removed, samples of mediastinal fluids were taken for culture, the pericardial sac was washed with antibiotic and povidone-iodine solutions. A drain for mediastinal irrigation and two tubes for drainage, one in the pericardium and one in the anterior mediastinum, were placed. If a pleural space was open, an additional drain was positioned just above the diaphragm. Sternal and wound debridement were performed. The sternum was not approximated. Skin and subcutaneous layers were full-thickness closed with nonabsorbable interrupted stitches. Mediastinal irrigation was performed alternating every 6 hours at 100 mL/h of 5% povidone-iodine saline solution and 100 mL/h of saline solution with antibiotics according to in vitro sensitivity. Intravenous antibiotic therapy according to the results of microbiology tests was continued all during mediastinal irrigation. On the seventh postoperative day the infusion was stopped, and swabs for culture were taken from the drains. If cultures were sterile, wound healing was satisfactory, fever and leukocytosis disappeared, then the drains were removed and the patient was discharged. If wound drainage or bacterial growth from cultures were observed, mediastinal irrigation was restarted and carried on another 7 days, and then drains were removed. When the infection recurred in spite of mediastinal irrigation, several alternative treatments were performed: secondary wound debridement and mediastinal irrigation for 7 days in 15 cases, open wound dressing with granulated sugar alone in 9 cases, open wound dressing with granulated sugar and hyperbaric therapy in 8, and plastic reconstruction with pectoralis flaps in 6 cases.
Definitions
Multiple variables were recorded prospectively and analyzed retrospectively as predictors of hospital death and prolonged (> 30 days) hospital stay. Hospital death was defined as death occurring during the hospital stay or within 30 days from the last surgical procedure. Comparisons of baseline demographics and preoperative, intraoperative, and postoperative variables were made between patients who died during their hospital stay and patients who were discharged. Further comparisons were performed between patients discharged before versus after postoperative day 30. Patients who died during their hospital stay were excluded from the analysis of length of hospital stay. Variables and their definitions are listed in Table 1.
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2 statistics for contingency tables, and odds ratios were test based. Multivariate analysis was conducted by multiple logistic regression. The p values for logistic regression analyses were computed by maximum-likelihood methods. All analyses were performed using the SPSS software version 8.0 (SPSS, Inc, Chicago, IL).
Limitation of the study
Although our diagnostic criteria and treatment protocols have mostly remained unchanged over the years, this study reviews a 20-year experience; therefore, modifications in diagnostic and surgical techniques can have added some bias to our results.
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Results |
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TopAbstractIntroductionPatients and methodsResultsCommentReferences |
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Wound healing was observed in 93 cases. Hospital stay ranged between 16 and 180 days (mean 31.3 ± 15.2). Germs isolated from wound secretions or from mediastinal fluid are reported in Table 2.
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Univariate analysis (Table 3) showed that length of cardiac operation more than 6 hours, cardiac transplant, blood losses in the early 24 postoperative hours more than 1,000 mL, length of postoperative intubation less than 24 hours, length of stay in intensive care unit (ICU) more than 96 hours, interval between onset of symptoms and wound debridement more than 20 days, positive wound cultures, positivity of cultures for both Gram-positive and Gram-negative species, culture positivity for Staphylococcus aureus, persistence of fever, and leukocytosis after wound debridement were associated with a significantly higher hospital mortality for DSWI.
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Comment |
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TopAbstractIntroductionPatients and methodsResultsCommentReferences |
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Many studies [2–13] have been performed to find out the risk factors for development of postoperative mediastinitis to lessen the incidence of such complications. Many factors have been found to increase the incidence of postoperative sternal infections. Some authors [9, 17] classified risk factors as preoperative, intraoperative, and postoperative factors. Although those risk factors have been well identified as causes of DSWI, unfortunately only few of these are modifiable [13]. Moreover, almost all patients undergoing cardiac surgery in the 1990s had at least two risk factors for developing postoperative DSWI.
The appropriate treatment of DSWI is still a matter of controversy: since Shumaker and Mandelbaum [18] proposed closed chest catheter irrigation, this has been the treatment of choice for DSWI, but in the recent years plastic procedures either with omental or pectoralis muscle flaps have reported to have a high rate of success and short hospital stay [17, 19, 20, 21]. Open wound dressing is no longer employed as the primary treatment of DSWI, having a high rate of morbidity and unacceptably longer hospital stay [24].
Mortality after DSWI is still high, ranging between 5% and 47% in spite of early diagnosis and appropriate treatment [5, 6, 10, 14, 17]. Although some authors [19] reported no hospital mortality in small series including patients with sterile sternal dehiscence and with DSWI undergoing either closed chest irrigation and pectoral muscle flap, mortality for DSWI is still high. The Duke’s series of patients who underwent CABG [21] reports an 8.1% mortality rate in patients with DSWI. Mortality rates in large series reported in the last decade range between 4.8% and 10.8% both in patients undergoing plastic procedures and in those treated with closed chest irrigation [20, 22, 23]; therefore neither plastic procedures nor closed chest irrigation has proved in large series to reduce the mortality rate for DSWI below 4%.
Our series reports a mortality of 16.9% over 20 years, including patients who had undergone cardiac transplant and those operated upon during deep hypothermia and circulatory arrest for type A aortic dissection. Moreover, only patients with DSWI were included in our series, and those with sterile sternal instability were not considered in this study.
Our study shows that although demographic variables or those related to associated diseases such as diabetes and renal and hepatic insufficiency are risk factors in determining DSWI, they are not significant predictors of hospital death and prolonged hospitalization. It is surprising to note that although bilateral mammary artery harvesting in CABG procedures is associated with a significantly higher incidence of postcardiotomy DSWI in diabetic patients [1–8], it was not found to affect the outcome of the infection in our series.
The most significant variables predicting a bad outcome after DSWI were those related to postoperative management. Appropriate postoperative management can heavily influence DSWI prognosis. In our study the time between the onset of symptoms and wound debridement has been one of the most important factors affecting DSWI prognosis. Delay in reoperation allows time for the infection to spread deeply into the chest cavity causing sepsis, involvement of cardiac sutures, and sternal osteomyelitis. Moreover persistence of fever and leukocytosis after wound debridement adversely affects DSWI prognosis. It is obvious that such conditions are signs of inappropriate wound debridement and this should lead to a policy of timely surgical reexploration and accurate wound debridement.
Postoperative bleeding has been associated with significantly higher mortality in patients with DSWI. Although reoperation for bleeding does not influence DSWI prognosis, an amount of postoperative bleeding more than 1,000 mL/24 hours has been a strong determinant for DSWI outcome. Such results support evidence that timely surgical reexploration for bleeding may improve the prognosis of patients with DSWI. On the other hand, delay in surgical hemostasis can lead to retrosternal blood collection and consequent need for blood transfusion. Such conditions provide optimal local conditions for bacterial growth together with systemic immunodepression [25], thus worsening the prognosis of the infection.
Length of postoperative intubation and stay in intensive care are predictors of bad outcome after DSWI. Although such conditions are generally associated with poor preoperative cardiac function and severely disabling cardiac disease, they also allow postoperative wound contamination from the upper airways and secondary immunodepression caused by aggressive antibiotic therapy. Therefore fast-track protocols may improve DSWI prognosis.
In conclusion, risk factors for the development of complications of postoperative mediastinitis are mostly not modifiable. Furthermore, widening of indications for cardiac surgery will increase the number of patients with multiple risk factors. Nevertheless, our study shows that the prognosis of DSWI can be influenced by adequacy and quickness of treatment. Demographic variables and associated diseases do not affect DSWI prognosis, whereas prompt surgical reexploration for bleeding and early and proper wound debridement may significantly reduce mortality and morbidity after DSWI.
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References |
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TopAbstractIntroductionPatients and methodsResultsCommentReferences |
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