The predictors of surgical site infection post cardiac surgery: A systematic review

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The predictors of surgical site infection post cardiac surgery: A systematic review Eyad Musallam, MSN, RN

We sought to conduct a systematic review to evaluate the predictors of surgical site infection (SSI) after cardiac surgery. We included published, peer-reviewed, English-language, retrospective and prospective studies identified in a search of Medline, CINAHL, and PubMed from 2005 and through February 20, 2012. The studies involved adults (age >18 years) undergoing cardiac surgery (defined by ICD-9 codes) and could be of any study design, in English, published within last 7 years, with data collection taking place in United States within last 10 years. We excluded animal studies, duplicates, summaries, commentaries, editorials, case reports, studies that conducted outside United States, and studies published before last 7 years or studies with data collection take place before last 10 years (2002). Three types of predictors emerge: Predictors of general infection post cardiac surgery, predictors of micro-organisms’ specific SSIs and tracheotomy, and allogenic blood transfusion as specific predictors of SSI. Although the reviewed articles cover wide range of SSIs predictors, none of these articles investigate preoperative skin preparation, using pre- and postoperative prophylaxes antibiotics, postoperative wound care (appropriate time for first dressing), and patient nutritional status as a predictors of SSIs after cardiac surgery. Investigating these predictors for SSIs will enhance nurses’ understanding of the importance of specific types of nutrition in preventing SSIs and enhancing wound healing, implementing a protocol for the wound care postoperatively, and implementing a protocol for the use of prophylactic antibiotics. (J Vasc Nurs 2014;32:105-118)

More than 20% of healthcare-associated infections (HAI) are attributed to infection of a surgical site.1 Surgical site infections (SSI) are serious operative complications that occur in approximately 2% of surgical procedures.2 SSIs are an important category of HAI because they cause substantial morbidity, mortality, and prolonged length of hospital stay and result in high cumulative healthcare costs.2 There are three different types of SSI defined by the US Centers for Disease Control and Prevention (CDC). In the criteria put forth by the CDC, SSIs are classified as either incisional or organ/space, with incisional SSIs being further subclassified as superficial (involving only skin and subcutaneous tissue) versus deep (involving underlying soft tissue). Table 1 further elaborates on the CDC classification system, which has been widely adopted by surveillance and surgical personnel.3 Although advances have been made in last 10 years in infection control practices, including improved operating room ventilation, sterilization methods, barriers, operative technique, and availability of antimicrobial prophylaxis, SSIs remain serious operative complications.4 In 2002 in the United States, an estimated 14 million National Healthcare Safety Network operative procedures were performed.5 SSIs were the second most common HAI, accounting for 20% of all HAIs among hospitalized From the School of Nursing, University of Maryland Baltimore, Baltimore, Maryland. Corresponding author: Dr. Eyad Musallam, MSN, RN, School of Nursing, University of Maryland Baltimore, Baltimore, MD 21201 (E-mail: [email protected]). 1062-0303/$36.00 Copyright Ó 2014 by the Society for Vascular Nursing, Inc. http://dx.doi.org/10.1016/j.jvn.2014.01.003

patients.2,5 A similar rate was obtained from National Healthcare Safety Network hospitals reporting data in 20062008 (16,147 SSI after 849,659 operative procedures) with an overall rate of 1.9%.2,5 SSI can have a devastating impact on the patient’s course of treatment and is associated with increased treatment intensity, prolonged length of stay (LOS), higher costs, and substantial morbidity, mortality.1,2,5 SSI is associated with poor cosmetic outcome. Patients who have an unsightly wound experience emotional distress and have longer hospitalization or confinement at home.2 On average, SSI extended LOS by 9.7 days and increased costs by $20,842 per admission. From the US national perspective, these cases of SSI were associated with an additional 406,730 hospital days and hospital costs of >$900 million. An additional 91,613 readmissions for treatment of SSI accounted for a further 521,933 days of care at a cost of nearly $700 million.2 SSI is a serious complication after cardiac surgeries.6,7 The National Hospital Discharge Survey (National Center for Health Statistics) estimates that in 2009 in the United States, 242,000 patients underwent 416,000 cardiac surgeries. SSI has been reported in 2%-10% of these patients. It increases hospital costs for a cardiac surgery e from $15,000 to $30,000.8 Also, it causes an increment in the mean LOS ranged from 6 to 14 days.7,8 The mortality rate of patients who develop SSI post cardiac surgery is significantly more than the mortality rate of patients who do not develop SSI post cardiac surgery; it varies between 22% and 40%.7,8 Expanding our knowledge of the predictors for SSI after cardiac surgery is essential to developing targeted prevention strategies to reduce the risk of SSI. Determination of predictors for the development of SSI after cardiac surgery has been a major focus of surgical research owing to the significant morbidity, mortality, and increased costs associated with SSI. Previous studies have

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TABLE 1 U.S. CENTERS FOR DISEASE CONTROL AND PREVENTION SURGICAL SITE INFECTION (SSI) CLASSIFICATION SYSTEM Superficial incisional SSI: Infection occurs within 30 days after the operation and infection involves only skin or subcutaneous tissue of the incision and at least one of the following: 1. Purulent drainage, with or without laboratory confirmation, from the superficial incision. 2. Organisms isolated from an aseptically obtained culture of fluid or tissue from the superficial incision. 3. At least one of the following signs or symptoms of infection: Pain or tenderness, localized swelling, redness, or heat and superficial incision is deliberately opened by surgeon, unless incision is culture negative. 4. Diagnosis of superficial incisional SSI by the surgeon or attending physician. Deep incisional SSI: Infection occurs within 30 days after the operation if no implant is left in place or within 1 year if implant is in place and the infection appears to be related to the operation and infection involves deep soft tissues (eg, fascial and muscle layers) of the incision and at least one of the following: 1. Purulent drainage from the deep incision but not from the organ/space component of the surgical site. 2. A deep incision spontaneously dehisces or is deliberately opened by a surgeon when the patient has at least one of the following signs or symptoms: Fever (>38 C), localized pain, or tenderness, unless site is culture negative. 3. An abscess or other evidence of infection involving the deep incision is found on direct examination, during reoperation, or by histopathologic or radiologic examination. 4. Diagnosis of a deep incisional SSI by a surgeon or attending physician. Organ/space SSI: Infection occurs within 30 days after the operation if no implant is left in place or within 1 year if implant is in place and the infection appears to be related to the operation and infection involves any part of the anatomy (eg, organs or spaces), other than the incision, which was opened or manipulated during an operation and at least one of the following: 1. Purulent drainage from a drain that is placed through a stab wound into the organ/space. 2. Organisms isolated from an aseptically obtained culture or fluid or tissue in the organ/space. 3. An abscess or other evidence of infection involving the organ/space that is found on direct examination, during reoperation, or by histopathologic or radiologic examination. 4. Diagnosis of an organ/space SSI by a surgeon or attending physician.

documented an increased risk for SSI based on the NNIS criteria as well as other patient and operative characteristics.2,9,10 Previous studies that report predictors for SSI after cardiac surgery prominently included patients undergoing coronary artery bypass graft (CABG) surgery and that does not reflect all types of cardiac surgeries. During the last 10 years, however, with broader application of percutaneous coronary interventions, the population of patients undergoing cardiac surgery has changed substantially. An increasing proportion of patients are referred for complex and combined cardiac procedures such as multiple valve procedures, combined valve/CABG, or aortic procedures. Also, other surgical characteristics have changed dramatically over the last 5 years, such as surgical equipment, incision size, and antibiotics used after surgery.7,8,11 There were many changes in the characteristics of patients who underwent cardiac surgeries, the cardiac operative procedures themselves, and equipment that been used in the cardiac surgeries.12–15 These changes affect both SSI rates and risk factors of developing SSI. In patients’ characteristics, one study used 1,497,254 patients’ records from the Society of Thoracic Surgeons adult cardiac surgery database to characterize trends in patient characteristics and outcomes after CABG from 2000 to 2009.12 The results of this study showed a modest increase in diabetes mellitus (DM) and a significant increase in hypertension. Compared with 2000, patients undergoing isolated primary

CABG in 2009 were more likely to have DM (33% vs 40%) and hypertension (71% vs 85%). In addition, there was a 37% increase the number of patients who underwent PCI with or without stenting before undergoing CABG (19% vs 26%).12 The cardiac operative procedure itself was changed in the last decade in terms of type of anastomosis used in the procedures and the number of cases performed off-pump. There was a significant increase in the use of the internal thoracic artery. There has been an increase in the use of the left internal thoracic artery for coronary revascularization, increasing from 87.7% in 2000 to 94.7% in 2009. Also, the use of bilateral internal thoracic arteries increased slightly from 3.5% in 1999 to 4.1% in 2009. Cases performed off-pump increased from 14.5% in 2000 to 21.1% in 2009.12 Open heart surgery itself has undergone several iterative changes recently.13,15 In the mid 1990s, great enthusiasm existed for the ‘‘mid-CAB’’ (minimally invasive direct coronary artery bypass) procedure, an approach integral to ‘‘hybrid’’ revascularizations and primarily involving a small left anterior thoracotomy to harvest the left internal thoracic artery and expose the left anterior descending coronary artery. Introduction of mid-CAB procedures help to usher in the era of off-pump CABG, which was heralded as an approach to reduce the risks associated with on-pump CABG, particularly myocardial dysfunction and cerebrovascular complications.13,15 Finally,

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technology has introduced minimally invasive platforms for performing multivessel CABG, most recently the introduction of ‘‘totally endoscopic’’ and robotic CABG and valve surgery.15 Robinson from the University of Kentucky successfully utilized thoracoscopic-assisted takedown of the internal mammary artery and direct anastomosis through a mini anterolateral incision.15 Calafiore was the first to report an extensive experience in thoracoscopic-assisted CABG procedure off-pump through a small anterior thoracotomy incision, which is referred to as the MIDCAB procedure. The MIDCAB approach is designed for single vessel coronary artery disease in which the left internal mammary artery is anastomosed to the left anterior descending coronary artery or other vessels in the vicinity of the mini thoracotomy. A hybrid procedure is an approach for multivessel coronary artery disease still using minimally invasive techniques. This hybrid operation involves using the MIDCAB procedure for the left anterior descending anastomosis and percutaneous transluminal revascularization techniques by an interventional cardiologist with angioplasty and stent placement in the circumflex and right coronary artery circulations.13,15 The Port-Access system (HeartPort, Inc, Palo Alto, CA) was developed by cardiac surgeons and engineers at Stanford University to provide percutaneous transfemoral cardiopulmonary bypass (CPB) with endoluminal occlusion of the proximal thoracic aorta for direct antegrade cardioplegia delivery and retrograde cardioplegia delivery through a separately placed percutaneous transjugular catheter system. This system has allowed surgeons to perform CABG procedures through minimally invasive incisions with CPB support on the arrested heart. However, the goal of the robotic-assisted, totally endoscopic CABG at present eliminates the need for CPB. Thus, the Port-Access system is now used primarily in minimally invasive valve repairs and other robotic-assisted, open heart operations. Recently, the cardiac team at Columbia-Presbyterian Medical Center in New York performed the first totally endoscopic closed chest CABG in the United States. Ghitwood et al in North Carolina performed the first series of robotic-assisted simple and complex mitral valve repairs in the United States.13–15 These changes in patient’ profile and surgeries characteristics implies that predictors for SSI identified by old studies performed in less representative study populations are not applicable to current clinical practice. This systematic review discusses how several surgical modifications in the last 10 years have influenced the predictors of SSI, and examines whether the increased incidence of multiple comorbidities among cardiac patients during the recent decade adds new predictors to the previously known predictors list. The aims of this systematic review were to collect and summaries the existing data in recent studies reflect current clinical practice on reported predictors of SSI after cardiac surgery and to classify these predictors according to biophysiologic model. By reviewing the recent literature, recommendations will suggest aiming to reduce SSI after cardiac surgery.

DATA SOURCES AND SEARCH STRATEGY In this systematic review, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) were utilized to ensure the quality of the review.16 The aim of the PRISMA is to help authors improve the reporting of systematic reviews and

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meta-analyses. The PRISMA have focused on randomized trials, but PRISMA can also be used as a basis for reporting systematic reviews of other types of research. The PRISMA Statement consists of a 27-item checklist such as information sources, study selection, and risk of bias across studies.16 For the risk of bias across studies step, the PRISMA suggested using a tool to assess risk of bias. Many tools have emerged over the past 20 years to assess risk of bias. Some tools are specific to different study designs, whereas others can be used across a range of designs.16 In this review, the Quality Assessment Tool for Quantitative Studies were used to assess the risk of bias within the studies included in this review. The Quality Assessment Tool for Quantitative, developed by the Effective Public Health Practice Project, is a tool for doing knowledge synthesis (National Collaborating Centre for Methods and Tools).17 The Quality Assessment Tool for Quantitative Studies provides an overall methodologic rating of strong, moderate, or weak (National Collaborating Centre for Methods and Tools).17 Although the tool was developed by the Public Health Practice Project, it was developed to assess the methodologic quality of the primary studies with a variety of study designs and topics. The tool is used to evaluate the methodologic components of the reviewed studies rather than the content of these studies. A search to identify studies analyzing the predictors of SSI (according to CDC definition) after cardiac surgery was performed. The studies involved adults (age >18 years) undergoing cardiac surgery (defined by ICD-9 codes) and could be of any study design, in English, published within last 7 years, with data collection take place in United States within last 10 years. We excluded animal studies, duplicates, summaries, commentaries, editorials, case reports, studies that conducted outside United States, and studies with data collection taking place before 2002. This review includes only the studies conducted in United States to ensure a basic level of practice homogeneity in terms of open heart surgery utilization, regulation, guidelines, and technology advancements. Although this inclusion criterion will affect the generalizability of the review results, the results will be will accurately reflect the factors associated with SSI among the US population. Many studies showed that there are many differences across countries in term of open heart surgery utilization (practice variations) and outcomes.5,18,19 The result of comparing the United States and Canada, which belong to the same geographical region and have the same technology level, showed that per capita rates of CABG in the United States are at least 3-fold those in Canada. The in-hospital cost of CABG in the United States is substantially higher than in Canada. Compared with Canadian patients, US patients were older more likely to be female, and discharged from the hospital sooner (short LOS).18 The comparison between developed countries such as the United States or Canada and developing countries in Africa or Asia are much complicated because of the huge differences between these countries in term of technology, medical practice regulations, and guidelines and patients characteristics. For example, the result of studies conducted in the developing countries showed high rate of SSI #21%,19,20 whereas the US level is <2%-3%.12

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A comprehensive search of several electronic databases was conducted in PubMed (1809 to the present) provided by National Institutes of Health between (between 2005 and February 20, 2012); MEDLINE (1964 to current with Daily Update) provided by OVID Databases (between 2005 and February 20, 2012), and CINAHL provided by EBSCO Databases (between 2005 and February 20, 2012). In addition, we searched the reference lists of eligible studies and relevant reviews for additional published and unpublished data, searched by contacting several experts, and used the web search engine ‘‘Google Scholar’’ for abstracts. We used a combination of keywords related to predictors (risk factors, precipitating factors, and independent risk factors) and to the type of outcome (surgical site infection, wound infection, sternal wound infection, wound infection, and deep wound infection). We used the following search terms to search all trials registers and databases: Risk factors; precipitating factors; independent risk factors; surgical site infection; wound infection; sternal wound infection; superficial wound infection; deep wound infection; infection control; predictors; heart surgery; cardiac surgery; and thoracic surgery. Table 2 shows search strategy for one of the databases used in the search process. Two independent reviewers (T.S. and E.M.) screened all titles and abstracts to identify potentially eligible studies. The full text of these potentially eligible studies was then screened to determine the eligibility of the study for the review. Disagreements regarding eligibility were resolved by consensus with the help of other reviewer. The reviewers first screened all titles founded by search in the three databases after remove duplicates (125 titles); 82 titles did not match the systematic review topic. For example, articles that related to arterial and venous line infections were excluded. The remaining 44 titles were reviewed by abstract. A total of 24 articles were excluded under three major excluded criteria. First, 12 articles were excluded because the studies were not conducted in the United States. Second, 12 articles were excluded because the data were collected before 2002. Third, one study excluded because it investigates nonhuman subjects. Nineteen full articles were screened by the reviewer for inclusion and exclusion criteria, 10 studies take place outside United State were excluded. The search result was nine studies that met the inclusion criteria. Appendix 1 presents a flow diagram for predictors of surgical site.

RESULTS The search and review process result in seven studies. All studies were nonexperimental and descriptive. Three studies were prospective and four were retrospective. The sample size for these studies range from 246 to 331,429 patients who underwent cardiac surgery. All the study followed patients to detect the SSIs; the follow-up period ranged from during hospitalization only to 90 days post discharge. All studies use CDC definition of SSIs (dependent variable). Tables 3-6 provide detailed description of the reviewed studies. In this systematic review, 2 reviewers (E.M. and S.T.) independently rated study quality using the Quality Assessment Tool for Quantitative Studies (QATQS). This tool assesses study bias in eight areas: Sample selection, study design, confounding,

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TABLE 2 SEARCH STRATEGY USED IN MEDLINE/OVID DATABASE Strategy# :

MedLine/OVID Searches

Results

1 2 3 4 5 6

Surgical Wound Infection/ Surgical site infection.mp. Infection Control/ 1 or 2 or 3 Thoracic Surgery/ Cardiac Surgery.mp. or Thoracic Surgery/ Heart surgery.mp. 5 or 6 or 7 4 and 8 Limit 9 to ‘‘all adult (19 plus years)’’ Risk Factors/ Predictors.mp. 11 or 12 10 and 13

25,861 1,389 16,974 42,414 9,758 30,296

7 8 9 10 11 12 13 14

11,126 39,066 856 487 470,596 92,357 540,968 126

Searched for articles dated 2005-2012; last search made on February 20, 2012. Search was done in English. A total of 126 articles were found.

blinding, data collection methods, withdrawals and dropouts, intervention integrity, and analysis. The first six areas are each scored as strong, moderate, or weak, leading to an overall methodologic rating of study quality as strong, moderate, or weak. The last two areas, which are not scored, were used to better understand the results of the studies. Two studies were rated as strong, and the other five as moderate. The rating scale used to rate the level of evidence for each study was the Johns Hopkins Nursing Evidence-Based Practice Model. This model has three levels for rating the design of the research evidence, and three levels for grading the quality of the research evidence. According to this model, two studies rated as IIA and the other five studies rated IIB. The reviewed studies showed three types of predictors: Predictors of general infection after cardiac surgery, predictors of micro-organisms’ specific SSIs and tracheotomy, and allogenic blood transfusion as specific predictors of SSI.

Predictors of major SSI post cardiac surgery Three studies investigated the predictors of major SSIs post cardiac surgery. Two studies were retrospective21,22 and one prospective.23 According to QATQS, the studies conducted by Haas et al23 and Filsoufi et al21 are of moderate quality, whereas the study conducted by Fowler et al22 is strong. The result of these studies concludes 16 predictors for SSIs. Obesity, DM, and CPB time as predictors were consistent in the three studies.

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TABLE 3 REVIEW OF THE EMPIRICAL LITERATURE (PROSPECTIVE STUDIES)

Authors

Research Question

Independent Variable

Demographic Kanafani et al24 What is the information, incidence of preoperative postoperative parameters, S aureus intraoperative infections in variables, cardiac surgery postoperative patients? What are variables the preoperative risk factors for these infections? Haas et al23 Gender, diabetes, What are the risk smoker, age, factors for SSI BMI, duration after cardiac of surgery, LOS surgery? Is there before surgery, a relationship of total LOS nasal carriage of Staphylococcus species with the development of SSI? 27 Rogers et al Could allogeneic Demographic blood transfusion information, partially account preoperative for this gender parameters, difference in intraoperative SSI post cardiac variables, blood surgery? transfusion

Dependent Variable S aureus infections

SSI

Total Sample Size 16,386

246

Blood 150 female transfusion, 230 male infection, respiratory failure, death

Design

Study Setting

Prospective Multisite

Prospective Single site

Prospective Single site

BMI = body mass index; LOS = length of stay; SSI = surgical site infection.

With a sample size of 5,798 patients, Filsoufi et al21 conducted a study entitled, ‘‘Epidemiology of Deep Sternal Wound Infection in Cardiac Surgery.’’ This study was designed to identify the incidence, independent risk factors, and early and late survival after deep sternal wound infection (DSWI). In this study, the authors provide a general description of the predictors of SSI (mainly DSWI) post cardiac surgery. These predictors were surgery type (combined valve CABG surgery and aortic procedures), reexploration (reopening) for bleeding, CPB time more than 150 minutes or less than 150 minutes, preoperative LOS in hospital of more than 3 days, specific diseases (chronic obstructive pulmonary disease, DM, and history of myocardial infarction) and obesity measures (body mass index of >30 kg/m2). Filsoufi et al21 defined both the predictors and the outcomes. For example, they defined a patient with chronic obstructive pulmonary disease as one who requires bronchodilator therapy for >3 months to avoid disability from obstructive airway disease

or an forced expiratory volume in 1 second of <75% of the predicted value, or <1.25 L on room air, or a partial pressure of oxygen of <60. Also, the authors provide a clear definition for the investigated outcome (DSWI). The authors define DSWI (bone related) as any drainage of purulent material from the sternotomy wound and instability of the sternum. There were some limitations in this study.21 First, the study was retrospective in nature; therefore, the data collected were affected by the accuracy of the documentation. Second, although the sample size was large, the authors investigates more than three types of cardiac surgery, which affects the internal validity of the study. Fowler et al22 conducted a study of major infections after CABG. Their objectives were to identify the frequency of major infection after CABG, identify determinants of major infection among patients undergoing CABG, and convert these determinants into a bedside scoring system to estimate a patient’s risk

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TABLE 4 REVIEW OF THE EMPIRICAL LITERATURE (PROSPECTIVE STUDIES)

Authors

Duration of Follow-up

Follow-up Method

90 days

Clinical and microbiology data at 90 days

Haas et al23

During hospitalization only

Medical record during hospitalization and also for readmission

Rogers et al27

30 days

Lab results, pharmacy database, clinic visit

Limitation

Predictors were BMI > 40 kg/m2 (aOR, 1.9; 95% CI, 1.1-3.2), chronic renal failure (aOR, 1.8; 95% CI, 1.1-2.9), and chronic lung disease (aOR, 1.4; 95% CI, 1.0-2.0) Significant predictors for SSI were smoking and BMI. Of SSI micro-organisms, 65% were matched with results of nares cultures (5/8 cases).

It is a strong study. They use a prospective design with large sample size and multiple centers with 3 months follow-up a clear definition of SSIs. A single hospital, which will affect external validity (selection bias). Follow-up during hospitalization only, which is not effective because most SSIs develop after discharge.

aOR = adjusted odds ratio; BMI = body mass index; CI = confidence interval; RBC = red blood cells; SSI = surgical site infection.

Grade

Strong

IIA

Moderate

IIB

Moderate

IIB

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Women were more likely to receive allogeneic RBC or platelets than men. Patients who received allogeneic blood were 4.4 times more likely to develop an infection than those who did not. Women had a greater risk of infection.

Strength of Evidence

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Kanafani et al24

Results

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TABLE 5 REVIEW OF THE EMPIRICAL LITERATURE (RETROSPECTIVE STUDIES) Strength of Evidence

Duration of Follow-up

Follow-up Method

Rahmanian et al26

Mortality and DSWI at 40 days

Survival information for each patient was assessed by the Webbased Social Security Death index

Moderate

Fowler et al22

30 days

The STS National Cardiac Database was established in 1989 to report surgical outcomes after cardiothoracic surgical procedures.

Strong

Results

Limitation

Grade

DSWI occurred in 38 patients (1.3%): Patients with no respiratory failure. In multivariate analysis, respiratory failure was the strongest predictor of DSWI. BMI > exceeding 30 kg/m2 and diabetes are predictors for DSWI. BMI 40 kg/m2, hemodialysis, cardiogenic, age 85 years, immunosuppressive treatment, and diabetes mellitus. Also perfusion time 200-300 minutes, placement of an IABP, and the presence of three or more distal anastomoses. Infection associated with high mortality.

A single hospital, which affects external validity (selection bias). Retrospective study; quality of data collected depend on the accuracy of documentation.

IIB

Retrospective study. The data collected are affected by documentation accuracy. It examine all types of infections.

IIA

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Authors

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TABLE 5 CONTINUED

Authors

Strength of Evidence

Follow-up Method

Filsoufi et al21

5 years for survival and 30 days for infection

Mortality by web-based Social security index

Moderate

Garey et al25

30 days

Medical record, surgery, microbiology

Moderate

Results

Limitation

Grade

11 predictors were detected: obesity, DM, COPD, CPB time, LOS before surgery, reopening, respiratory failure, aortic surgery, combined valve CABG surgery, aortic calcification, and MI history. Mortality rate are higher within infected patients. LOS >48 h preoperative, DM, ventilator-dependent preoperative, and thoracocentesis were the main predictors for Gram-negative SSIs.

Retrospective study; data collected affected by documentation accuracy. Although the sample size was large, the authors investigate more than three types of cardiac surgery, which affects the internal validity.

IIB

Retrospective study; the data collected affected by documentation accuracy.

IIB

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Duration of Follow-up

BMI = body mass index; CABG = coronary artery bypass graft; COPD = chronic obstructive pulmonary disease; CPB = cardiopulmonary bypass; DM = diabetes mellitus; DSWI = deep sternal wound infection; IABP = intra-aortic balloon pump; LOS = length of stay; MI = myocardial infraction; STS = Society of Thoracic Surgeons.

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TABLE 6 REVIEW OF THE EMPIRICAL LITERATURE (RETROSPECTIVE STUDIES) Research Question

Design

Rahmanian et al26

Retrospective

What is the respective influence of respiratory failure and tracheostomy on the development of DSWI?

Fowler et al22

Retrospective

Filsoufi et al21

Retrospective

The objective of the study was to create and validate a bedside scoring system to estimate patient risk for major infection (mediastinitis, thoracotomy or vein harvest site infection, or septicemia) after CABG. What are the predictors of DSWI? What are the early and late outcomes of DSWI?

Independent Variable

Dependent Variable

Total Sample Size

Study Setting

Respiratory failure, demographic information, preoperative parameters, intraoperative variables, postoperative variables Demographic information, preoperative parameters, intraoperative variables, postoperative variables

DSWI

2,823 patients who underwent cardiac operations

Single site

For major infection

331,429 CABG

Multisite

Demographic information, preoperative parameters, intraoperative variables, postoperative variables

DSWI and 5-year survival

Infection occurred in 106 patients

Multisite

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(Continued)

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Authors

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Single site Gram-negative surgical wound infection Demographic information, preoperative parameters, intraoperative variables, postoperative variables surgery type

Predictors of micro-organism–specific SSIs

CABG = coronary artery bypass graft; DSWI = deep sternal wound infection.

What are the risk factors associated with Gram-negative bacteria surgical wound infection in patients undergoing cardiac surgery? Retrospective Garey et al25

Dependent Variable Independent Variable Research Question Design Authors

CONTINUED

TABLE 6

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of developing a major infection after CABG. The authors divided the predictors of general infection post cardiac surgery into preoperative predictors and intraoperative predictors. The preoperative predictors were body mass index of >40 kg/m2, hemodialysis, cardiogenic shock, age >85, immunosuppressive medication, and DM. Postoperative predictors were CPB time 200-300 minutes, placement of an intra-aortic balloon pump, and the presence of three or more peripheral anastomoses. In their study, Fowler et al22 defined both predictors and the outcomes explicitly. The study outcome was major infection post cardiac surgery. Major infection was defined as one or more of the following: (1) SSI (deep sternal wound, thoracotomy, or leg vein harvest site) or septicemia before discharge, or (2) readmission within 30 days of surgery for DSWI, leg wound infection, or septicemia. Infection was documented by at least one of the following: (1) Wound opened with excision of tissue (incision and drainage); (2) positive culture; or (3) treated with antibiotics. The Fowler et al22 study has some strengths in comparison with all reviewed studies; first, the authors used a large sample size (331,429 patients). Second, they investigated only one type of cardiac surgery (CABG), which enhances the internal validity of the study. Haas et al23 conducted a prospective study with a sample size of 246 patients from a single site to investigate the risk factors for SSI after cardiac surgery. They23 added smoking as a new predictor for SSI post cardiac surgery. Haas et al23 defined both predictors and the outcomes explicitly. The authors used the surgical site cultures for diagnosis SSI. Smoking history was determined by asking patients a yes or no question. Although this study has a strong design, the sample size was small and not sufficient to investigate many predictors.

Total Sample Size

Study Setting

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Two studies investigate the predictors of SSIs result from specific micro-organisms. Kanafani et al24 conducted prospective studies with a large sample size (n = 16,386), whereas Garey et al25 conducted a retrospective study with relatively small sample size (n = 2,590). According to QATQS, the studies conducted by Kanafani et al24 considered strong study, whereas the study conducted by Garey et al25 was considered a moderate study. Staphylococcus aureus and coagulase-negative Staphylococci account for >50% of the organisms associated with SSIs. In addition, Gram-negative bacteria such as Escherichia coli, Klebsiella spp, Enterobacter spp, and Pseudomonas aeruginosa can account for #35% of pathogens.11 Depending on these facts, Garey et al25 and Kanafani et al24 propose that studying the predictors and risk factors for micro-organism–specific SSI is important; if predictors or risk factors for development of SSI owing to specific micro-organisms are different from those for other types of SSIs, unique interventions may be necessary to prevent these SSIs. In addition, identification of these risk factors or predictors would allow clinicians to identify the patient cohort who would most likely benefit from empiric antibiotics with activity against specific micro-organisms in patients with SSIs. Garey et al25 conducted a study 2,590 patients to define risk factors associated with Gram-negative sternal wound infections in patients undergoing cardiac surgery. They found that a preoperative stay of >48 hours, tracheotomy use, ventilator

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dependency before surgery, and thoracocentesis were major significant predictors for Gram-negative sternal wound infections. They also found that advanced age and peripheral vascular diseases were associated with Gram-positive bacteria. In addition, DM was associated with both Gram-negative and -positive wound infections. Although Garey et al25 had a large sample, this sample was from a single hospital and this may affect the external validity of the study. Also, the quality of the data in this retrospective study depends on the quality of data documentation by the hospital. Kanafani et al24 conducted a study of 16,386 patients to describe the epidemiology of major S aureus infections after cardiac surgery and to identify and validate preoperative risk factors associated with these infections. The result of this study showed that patients with BMI of >40 kg/m2, chronic renal failure, or chronic respiratory diseases have higher risk of developing major S aureus infections after cardiac surgery. This study used the strongest design, with a large sample size from multiple sites. All these factors consider strength points that enhance the internal and the external validity of the study.

Tracheostomy and allogenic blood transfusion as specific predictors of SSI Two studies investigated whether specific factors would predicts or result in SSIs post cardiac surgery. These studies were conducted by Rahmanian et al26 and Rogers et al.27 Rahmanian et al26 conducted a retrospective study of 2,823 patients to investigate the influences of respiratory failure and tracheostomy on the development of DSWI. Rogers et al27 conducted a prospective study of 380 patients to investigate allogenic blood transfusion as an independent predictor of SSI among women who underwent cardiac surgery. Both studies were of moderate quality according to QATQS. In the subgroup of patients who required prolonged or repeated endotracheal intubation, tracheostomy offers several potential benefits, including reduced sedation requirements, reduction in the incidence of pneumonia, reduction in the work of breathing, and more rapid weaning from mechanical ventilation. It has, however, been suggested that tracheostomy after median sternotomy is associated with an increased risk of DSWI.10 Rahmanian et al26 hypothesized that respiratory failure, rather than tracheostomy, is a risk factor for DSWI in cardiac surgery patients. They designed a study to analyze the respective influence of respiratory failure and tracheostomy on the development of DSWI. The result of this study showed that the incidence of DSWI remains high in patients with respiratory failure. Tracheostomy is not a risk factor for DSWI and serves as a surrogate for respiratory failure. Although Rahmanian et al26 utilized the strongest design for this study, their small sample size drawn from single site may affect the external validity of this study. Blood transfusion is the most common procedure during hospitalization, and its use has increased by 64% from 1997 to 2003. Cardiac surgery accounts for approximately 20% of all allogeneic blood transfusions in the United States, although there is considerable variability among hospitals regarding the amount of blood components administered. Although transfusion may be necessary to prevent or treat tissue hypoxia, the immunomod-

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ulatory effects of allogeneic blood transfusion have been recognized for decades. Transfusion-related immunomodulation has been shown to result in an increased risk of nosocomial infection and mortality in various patient cohorts.11,28 The decision to prescribe a transfusion conventionally rests on threshold levels of hemoglobin or hematocrit. Because normal hemoglobin and hematocrit levels are lower in women than men, women are more likely than men to receive a blood transfusion.11,28 Based on this background, Rogers et al27 conducted a study to investigate allogenic blood transfusion as an independent predictor of SSI among women who underwent cardiac surgery. The result of this study was that patients who received allogenic blood transfusion were 4 times more likely to develop infection post cardiac surgery. Although Rogers et al27 utilized the strongest design for this study, their small sample size drawn from single site may affect the external validity of this study.

IDENTIFIED KNOWLEDGE GAPS In this systematic review, all articles present predictors of SSIs post cardiac surgery. These predictors were general predictors, micro-organism–specific predictors (predictors of Gramnegative bacteria), and procedure-related predictors (blood transfusion). The reviewed articles investigate three categories of predictors: Surgical consideration predictors (surgery type, reopening, and tracheotomy use), preoperative and intraoperative predictors (blood transfusion, hospital stay before surgery, ventilator dependency before surgery, etc.) and patient-related predictors (chronic obstructive pulmonary disease, DM, obesity, advanced age, and smoking history). These predictors may causes SSIs post cardiac surgery through three common path physiologic pathways: Decreased collagen synthesis, vasoconstriction, and increased immunosuppression. Although the reviewed articles cover a wide range of SSIs predictors, none investigated preoperative skin preparation, using preoperative and postoperative prophylactic antibiotics, postoperative wound care (appropriate time for first dressing), and patient nutritional status (which directly affects collagen synthesis) as a predictors of SSI s after cardiac surgery. For most SSIs, the source of the pathogen(s) comes from the patient’s skin, mucous membranes, or bowel and rarely from another infected site in the body (endogenous sources).11,29 Investigating skin preparation modalities such as hair removal and bathing with antimicrobial soap will build evidence for best nursing practice and help nurse managers to develop and implement a protocol for appropriate preoperative skin preparation. The purpose of preoperative antibiotic prophylaxis is to reduce the impact of intraoperative microbial contamination of a surgical site to a level that will not result in infection. Antibiotic prophylaxis must be aimed at the bacteria most likely to infect the wound, be of the narrowest spectrum required, and be delivered in a timely manner.30 Investigating types of antibiotics used, antibiotic duration, and timing, and comparing the effectiveness of these antibiotics results in the development and implementation of a protocol for the use of prophylactic antibiotics.

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Although postoperative wound care and dressing is wellinvestigated in the literature (by a simple search of PubMed that will provide not 366 articles on wound care, but 366 pages of articles), the investigation of timing for first dressing as predictor for SSIs is important. Timing of the first postoperative dressing affects the inflammatory phase of wound healing.30 The duration of the inflammatory phase of wound healing is about 2-3 days. Investigating whether to cover the wound for 2-3 days affects the wound infection rate, and helps in developing and implementing a protocol for the wound care postoperatively. Collagen synthesis is an important process in wound healing and prevents infection. This process depends mainly on patient nutritional status, which is why the collagen synthesis process requires both amino acids and vitamin C.31 Investigating nutritional status as a predictor for SSIs will enhance nurses’ understanding of the importance of specific types of nutrition in preventing SSIs and enhancing wound healing. Diabetes is a well-documented risk factor for SSI after CABG.21,32 High perioperative blood glucose concentrations have been identified as a risk factor for SSI after thoracic surgery.24,25,33 Postoperative hyperglycemia in patients with diabetes has also been associated with adverse outcomes such as death, myocardial infarction, stroke, and septic complications before hospital discharge.24,33–35 At a biochemical level, it is known that hyperglycemia increases the inflammatory response by activating key proinflammatory transcription factors that are normally suppressed by insulin such as nuclear factor-kB, activated protein-1, and early growth response-1. In addition, hyperglycemia also directly affects pathways responsible for changes in endothelial function, inflammation, and oxidative stress. These changes in the endothelial function, inflammation, and oxidative stress affect the graft patency and may result in recurrent ischemic events, as well as an increased need for revascularization procedures in CABG patients with DM.36 Maintaining serum glucose of #180 mg/dL with continuous insulin infusions in patients with and without DM reduces morbidity and mortality, lowers the incidence of sternal wound infections, reduces hospital LOS, and enhances long-term survival. Patients who require >3 days of ventilatory support or develop sepsis or multiorgan failure should have serum glucose levels of <150 mg/dL.37 More research are needed to answer the following questions: What is the optimal level of glycemic control? Which, if any, specific time period is most crucial for maintaining glycemic control? What is the optimal method to measure glucose values in the perioperative period? This systematic review has some strengths and limitations. The strengths of this review were that we followed strict guidelines as presented by the PRISMA statement in term of study selection and evaluation. To ensure that all the studies included in this review reflect the same basic level of technology and practice, this review only includes studies conducted in the United States. A limitation of this review is that the results generalize only to the US population. Second, despite searching in a multi-method, comprehensive manner, electronic research indexing is generally problematic and, therefore, we may have missed some key literature.

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Appendix 1 FLOW DIAGRAM FOR SURGICAL SITE INFECTION PREDICTORS REVIEW

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