Antimicrobial Prophylaxis in Surgery



Introduction





Surgical site infection (SSI) is the most common complication in surgical patients. Significant advances have occurred over the last few decades resulting in better understanding of the relevant risk factors for SSI, and high-level evidence has identified specific preventive strategies that help reduce the incidence of SSI. With the introduction of asepsis and antisepsis, prophylactic antibiotics have had the most significant impact reducing the incidence of SSI. However, in order to achieve the benefits derived from their use and minimize potential undesired effects, practice of this strategy needs to follow specific basic principles.






This chapter reviews the epidemiology and clinical impact of SSI, describes the role of prophylactic antibiotics as a preventive strategy, and expands on the specific principles that guide their appropriate use. We will also summarize specific recommendations for different procedures while highlighting important aspects of different antibiotic regimens. Lastly, we will identify specific barriers to this practice and identify some health service interventions proven to improve past and current practice patterns when using antibiotic prophylaxis.






Rationale for Use of Antimicrobial Prophylaxis





Surgical Site Infection Epidemiology and Risk Factors



It is estimated that over 40 million surgical procedures are performed every year in the United States. SSIs complicate approximately 2–5% of these procedures, representing 38% of nosocomial infections occurring in surgical patients. Risk factors for SSI can be classified as patient-related factors and local/surgical factors, and can be stratified into modifiable or potentially modifiable, and nonmodifiable risk factors. Modifiable risk factors include elective operations in the presence of associated infections, prolonged preoperative hospital stays, seromas, dead space, foreign bodies, routine drain use, among others, and can be modified with the use of good surgical practice and specific preventive strategies. Nonmodifiable risk factors are most commonly patient related and have an important effect on the incidence of SSI for each individual patient. The wound class (Appendix 1) is a relatively good predictor of SSI and has traditionally been used to estimate the risk of SSI and as a benchmark for interinstitutional comparisons. However, with the more recent understanding of SSI and its multifactorial risk factors, different predictive scores, such as the National Nosocomial Infection Surveillance (NNIS) score, have been developed to better estimate the risk of SSI for each individual patient after considering the interaction between different risk factors (Table 50-1). Specific preventive measures have been identified and are used to decrease the risk of SSI. These include minimizing the presence of microorganisms (eg, prophylactic antibiotics), and optimizing the patient’s ability to fight those still present at the surgical site, during the perioperative period.




Table 50-1 National Nosocomial Infection Surveillance (NNIS) System Classification for Determining the Risk of Surgical Site Infection 






Impact of Surgical Site Infection



The effect of SSI on patients and the healthcare system is significant. Patients with SSI are more prone to develop additional complications, including wound dehiscence, hernia, and complicated infections such as necrotizing soft tissue infections. Multiple large, single-center, multicenter, and population-level analyses have revealed at least a twofold increased risk of postoperative mortality in patients with SSI. Additionally, SSI is associated with longer hospital stays (10–12 excess days), a higher risk of intensive care unit (ICU) admission, and a fivefold higher risk of hospital readmission. Similarly, the treatment of patients with SSI results in an excess cost of over $5000 per patient, representing a U.S. national cost between $130 and $845 million per year. As such, and given the availability of multiple preventive measures, SSI is not only considered a significant surgical complication but is also used as a healthcare quality indicator.






Goals of Antimicrobial Prophylaxis



Based on the preceding considerations and high-level evidence-based data, antimicrobial prophylaxis is a preventive strategy used with the primary goal of reducing the risk of SSI. As such, antimicrobial prophylaxis is used as a preventive strategy when infection is not present but the risk of postoperative SSI is present. The efficacy and effectiveness of this practice are measured by its impact on the incidence of SSI, and its principles as well as developed guidelines are tailored toward achieving an improvement in this specific outcome. Additionally, the practice of antimicrobial prophylaxis should follow strict guidelines to maximize its benefits while minimizing undesired effects such as emergence of resistant bacteria or potential—although rare—side effects in individual patients at low risk of developing SSI.



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Practice Point




Antimicrobial prophylaxis is used as a preventive strategy when infection is not present but the risk of postoperative SSI is present.



  • The relative benefit of antibiotic prophylaxis holds for all cases, but the absolute benefit and the number needed to treat or prevent an SSI are less for procedures with a low baseline risk of infection.
  • The decision to use prophylaxis should be based on a complex assessment of the risk of infection and the cost and morbidity of the infections that might occur for that procedure, all balanced against the cost of the prophylaxis including its price and the potential for adverse effects including allergies, superinfections, and the generation of bacterial resistance by overuse.






Common Principles





Indications for Antibiotic Prophylaxis



John Burke first described the value of prophylactic antimicrobials in the 1950s with animal studies that clearly demonstrated the principles of prophylaxis that are still followed today. Since then, many retrospective studies, prospective randomized trials, systematic reviews, and meta-analyses have confirmed the efficacy of prophylactic antimicrobials in decreasing the risk of SSI and established the basic principles. The magnitude of this effect directly relates to the magnitude of the risk of SSI. The majority of studies have focused on evaluating the efficacy of prophylactic antibiotics when used for specific operations. This has resulted in high-level data supporting their use for clean-contaminated and contaminated operations, and more controversial data for their use in operations classified as clean. However, the risk of SSI can vary significantly between patients undergoing similar surgical procedures. Various studies have shown that using a more comprehensive predictive tool (such as the NNIS score), the risk of SSI can in fact be higher for some patients with less contaminated wounds, depending on the presence of other risk factors. This has been supported by randomized trials and meta-analyses demonstrating a clinical benefit of using prophylactic antibiotics for breast, cardiac, orthopedic, and vascular surgery, as well as other clean operations.



More recently, Bowater and colleagues published a paper assessing the overall general benefit of prophylactic antibiotics independent of the specific operative procedure.1 They performed a meta-analysis of available meta-analyses on the topic and collated the data from studies assessing their efficacy in different types of procedures. This paper concluded that the use of prophylactic antibiotics is an effective practice that reduces the risk of SSI, regardless of the operation, and the decision to use prophylaxis should take this into consideration.



The relative benefit of antibiotic prophylaxis holds for all cases, but the absolute benefit and the number needed to treat to prevent an SSI are less for procedures with a low baseline risk of infection. The decision to use prophylaxis should be based on a complex assessment of the risk of infection, the cost, and the morbidity of the infections that might occur for the procedure, all balanced against the cost of the prophylaxis, including its price and the potential for adverse effects such as allergies, superinfections, and the generation of bacterial resistance by overuse. Based on this type of reasoning, patients in whom a prosthesis (implantation of any foreign body) is to be used or for those having cardiac operations, for example, have long been considered appropriate cases to receive prophylaxis even though the procedures are “clean” and the relative risk of SSI is fairly low. Clearly, an SSI in a patient with a recent hip replacement or after a coronary artery bypass grafting (CABG) procedure has more morbidity than that presenting after removal of a subcutaneous lipoma of the trunk. With these considerations, the use of antimicrobial prophylaxis should be based on a preoperative risk assessment that takes into consideration other variables in addition to wound classification, as well as the potential consequences of this complication.



Based on existing data and the foregoing considerations, prophylactic antibiotics are indicated for the following:




  • Clean-contaminated and contaminated operations
  • Clean operations with a high risk of SSI

    • NNIS score ≥ 1 +/− other associated important risk factors
    • Immune-compromised host
    • Other clean operations with known increased risk of SSI, such as groin incisions and mastectomy

  • Clean operations for which SSI has significant clinical consequences

    • Examples: operations involving placement of prosthesis (eg, joint replacements, mesh hernia repairs, etc), craniotomy, and cardiac and vascular operations






Selection of Antimicrobial Agent



The characteristics of the ideal agent for effective antibiotic prophylaxis include (1) appropriate bactericidal effect on the bacteria expected to be present at the surgical site, (2) adequate biodistribution in the surgical site, (3) low risk of potential side effects (allergic reactions, Clostridium difficile colitis, change in resistance patterns, etc), and (4) low cost. The majority of guidelines helping to choose the appropriate agent are based on randomized trials in which a specific antibiotic regimen has been tested for a specific procedure. We support the use of this evidence-based decision making. However, the vast majority of procedures are prone to SSI with similar species of bacteria, and similar types of antibiotics have been tested. If clinical trial data are not available for a specific procedure, it is reasonable to generalize from trial data on procedures with comparable bacterial flora and risk.



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Practice Point




The characteristics of the ideal agent for effective antibiotic prophylaxis include:




  1. Appropriate bactericidal effect on the bacteria expected to be present at the surgical site.



  2. Adequate biodistribution in the surgical site.



  3. Low risk of potential side effects (allergic reactions, C. difficile colitis, change in resistance patterns, etc)



  4. Low cost.




In general, the first consideration is to determine the class of wound and the most common bacteria causing SSI in each case. For clean wounds, skin flora with gram-positive bacteria are the most common pathogens causing SSI. For these operations, cefazolin is the most commonly used antibiotic, and it follows the four main principles already outlined. Alternatives to this agent include other first- or second-generation cephalosporins, oxacillin, and clindamycin, among others. For patients with documented and clinically relevant betalactam allergies, clindamycin or vancomycin is an adequate alternative. For procedures with expected gram (−) +/− anaerobic bacteria, such as most clean-contaminated and contaminated operations, coverage for these pathogens must guide antibiotic selection. Specific regimens include single agents such as ertapenem, cefotetan, and cefoxitin or multiple-agent regimens such as an aminogly-coside or a quinolone plus clindamycin or metronidazole (Table 50-2).




Table 50-2 Recommended Antibiotic Prophylaxis Regimens for Different Types of Surgical Procedures Based on Published Guidelines and Most Current Available Data