By Bonnie M. Barnard, MPH, CIC
Postoperative surgical site infections (SSIs) are a major source of morbidity in the United States. Among the 27 million people undergoing surgery annually, approximately 500,000 will acquire a nosocomial SSI. SSIs are the third most commonly reported nosocomial infection.
A 1992 analysis of these infections showed that each SSI prolonged length of stay seven to nine days and resulted in an added cost of more than $3,000 per infection.1
SSIs can be classified as incisional and organ/space manipulated during an operation. Incisional infections are further divided in superficial (skin and subcutaneous tissue) and deep (deep soft tissue muscle and fascia). Deep incisional and organ/space are the types of SSIs that cause the most morbidity. Definitions of SSIs can be found in the Centers for Disease Control and Prevention (CDC)'s Guideline for Prevention of Surgical Site Infection, 1999.2
Infections may be caused by endogenous (e.g., bacteria on the patient's skin) or exogenous sources (e.g., personnel, the environment or materials used for surgery). Most SSIs are caused by the patient's own bacterial flora. The most common microorganisms causing surgical site infection are Staphylococcus aureus (20 percent), Coagulase negative staphylococcus (14 percent) and enterococcus (12 percent).3
Factors that expose patients to increased risk for SSIs include diabetes, nicotine use, steroid use, obesity, malnutrition, prolonged preoperative stay, preoperative nares colonization and perioperative transfusion. Other preoperative and intraoperative risk factors for SSIs are:
Optimization of Antimicrobial Prophylaxis
One of the most important interventions in preventing SSIs is the optimization of antimicrobial prophylaxis. Its purpose is to provide a brief course of an antimicrobial agent in order to reduce the microbial burden of intraoperative contamination to a level that cannot overwhelm host defenses. It is not an attempt to sterilize tissues, but a critically timed adjunct to other SSI prevention measures.4
There are five professional references that are generally referred to for information on the proper type, route and timing for antimicrobial prophylaxis:
In general, the five groups agree in principle on most surgical procedures and drugs. There are some discrepancies in relation to dosing and timing, but these differences are not significant in practice.
Optimal surgical antimicrobial prophylaxis must take into consideration the following three factors:
1. Appropriate choice of antimicrobial agent
2. Proper timing of the antibimicrobial prior to the incision
3. Limiting the duration of antimicrobial administration after surgery
Appropriate Antimicrobial Agent
The choice of drug has to do with its clinical efficacy and whether it is safe, inexpensive and has a wide spectrum. It should be "active against the pathogens most commonly associated with wound infections following a specific procedure and against the pathogens endogenous to the region of the body being operated on."5
For elective clean procedures using a foreign body, and in clean contaminated procedures, it is generally recommended that a single dose of cephalosporin (e.g., cefazolin) be administered intravenously by anesthesia personnel in the operative suite just before the incision.
Proper Timing of Antimicrobial Administration
It is important that the antibiotic infusion is timed so the optimal concentration is in the serum/tissue at the time of the incision. It is equally important to maintain that therapeutic level in the serum/tissue throughout the operation. If the surgical procedure is longer than the half-life of the drug, the drug must be re-dosed during the procedure.
Historically, the drug should be given during the interval between 30 minutes and two hours before the time of surgical incision. The most recent Medical Letter recommendations are that the drug be given no more than 30 minutes before the skin is incised.
Limiting the Duration of Antimicrobial Administration
Discontinuation of the antibiotic within 24 hours after surgery is recommended for two reasons:
1. Use of the surgical prophylaxis antimicrobial agent past this time frame has not been shown to improve SSI rates and increases the cost of care unnecessarily.
2. Indiscriminate use of antimicrobials can lead to the development of antibiotic resistant microorganisms.
In a prospective study of 2,641 coronary artery bypass graft (CABG) patients, two outcomes were measured: incidence of SSIs and isolation of a resistant pathogen. There was no statistical difference in SSI rates between those who received less than 48 hours of antimicrobial prophylaxis vs. those who received more than 48 hours of antimicrobial prophylaxis (8.7 percent vs. 8.8 percent p=1.0). Furthermore, the odds of developing a resistant pathogen was 1.6 times greater (95 percent CI 1.1-2.6) in patients who received more than 48 hours of antimicrobial prophylaxis after the surgery.6
The Centers for Medicare and Medicaid Services (CMS) and the CDC have developed a new national healthcare quality improvement project to prevent postoperative infection. The Surgical Infection Prevention (SIP) Project will be rolled out via the quality improvement organizations (QIOs) in all 50 states in August 2002. The focus of this project is the prevention of SSIs through the optimal selection and timing of prophylactic antibiotics administration, both known to be important in effective prophylaxis.
The indicators for the project will include:
Typically, ICPs and surgical staff focus on measuring outcomes (i.e., surgical site infection rates). Because there are processes of care that have been shown to affect SSI outcomes, this project is focused on measuring the processes of care critical to outcomes, rather than measuring the outcomes themselves. This approach is easier for several reasons. Because the focus is on process measures rather than outcome measures (SSI rates) there is no requirement for risk adjustment (as there is an outcome measure for SSI rates). Additionally, relative achievable improvements in processes are generally much larger than in outcomes, and measuring processes can be done in rapid cycles (rapid cycle PDSA) for fast feedback and improvement.
These indicators will be monitored for the following procedures: coronary artery bypass graft; other cardiac procedures; colon; hip and knee arthroplasty; abdominal and vaginal hysterectomy; and vascular procedures. QIO staff in each state will work with hospitals to improve these very important indicators of optimal SSI prevention practices. For more information on this project, visit www.surgicalinfectionprevention.org or contact your state's QIO (formerly known as Peer Review Organization or PRO).
What's On the Horizon?
It has been shown that proper administration of prophylactic antibiotics can decrease surgical site infections by 40 percent to 80 percent. Unfortunately, there is evidence that even with proper antibiotic prophylaxis, in the face of breakdowns in wound management or antisepsis, patients still get wound infections. Many risk factors for wound infection are things over which the physician has no control, such as gender, age, obesity, underlying diseases and length of surgery. Now that we know how to minimize the chance that endogenous bacteria may cause a surgical site infection, what is next?
Enhanced Perioperative Glucose Control in Diabetic Patients
There is evidence to show a relationship between hyperglycemia (glucose greater than 200) during the first 48 hours following surgery and an increased risk of SSI.7 In addition, in a prospective, sequential study of 2,467 diabetic patients undergoing cardiac surgery from 1987 to 1997, those who received intermittent subcutaneous insulin had a higher rate of deep sternal SSI than those who received continuous intravenous insulin during the procedure (2.0 percent vs. 0.8 percent p=.01)8
These two studies show that tight control of blood glucose levels in the perioperative period may lead to better SSI outcomes in diabetic and non-diabetic patients.
Supplemental Perioperative Oxygen Therapy
Administration of supplemental perioperative oxygen may decrease SSI rates. In a randomized controlled trial, double blinded among 500 colorectal surgery patients, those who received 80 percent inspired oxygen during and up to two hours after surgery had a lower incidence of SSI than those patients who received 30 percent inspired oxygen (5.2 percent vs. 11.2 percent; p=.01).
In a study of 2,231 CABG procedures from 1991 to 1994 at a tertiary care center, it was found that implementation of a comprehensive infection control program decreased SSIs, even after adjusting for potential confounding co-variables. The program consisted of: prospective surveillance; quarterly reporting of SSI rates; chlorhexidene showers; discontinuation of shaving; administration of antibiotic prophylaxis in the holding area; elimination of ice baths for cardioplegia solution; limitation of operating room traffic; minimization of flash sterilization and elimination of postoperative tap-water wound bathing for 96 hours.9
Improvement of Outcomes
So how do hospitals improve the processes of care known to impact SSI rates? The experience of the National Nosocomial Infection Study (NNIS) states there are several key components to programs that have been successful in preventing nosocomial infections. In reviewing the activities of the facilities participating in the NNIS program, the staff discovered three key components of a successful prevention effort:
1. Use of a multidisciplinary team to build consensus that a problem existed, disseminate information about the infection and any planned interventions to their colleagues and assist ICPs with investigations and prevention;
2. Educational sessions to introduce interventions and;
3. Data dissemination to show the impact of the interventions.
They emphasized the importance of sharing success stories and outlining epidemiologic approaches to understanding and describing best practices.10 This sharing can be between facilities or among staff within your own facility. It is the people working at the point-of-care that have the most to contribute to any improvement process and get them involved from the beginning. To ensure a SSI prevention program will succeed, stay focused on the measurement and improvement of the processes of care that have been shown to directly impact surgical site infections while using outcome measures as "stepping stones." P
Bonnie M. Barnard, MPH, CIC, is an infection control professional with 18 years of experience in hospitals, long-term care and in the outpatient setting. She has been certified in infection control since 1984, and has published and presented abstracts on many subjects related to infection control. Barnard teaches and presents on infection control and patient safety topics, and serves on the board of directors of the Association for Professionals in Infection Control and Epidemiology (APIC).
Association for Professionals in Infection Control and Epidemiology (APIC)
Society for Healthcare Epidemiology of America (SHEA)
Association of periOperative Registered Nurses (AORN)
Centers for Medicare & Medicaid Services - Centers for Disease Control
Surgical Infection Prevention Project