|WOUND CARE MANAGEMENT: Risk Factors for Surgical Site Infections
|Marcia Spear ACNP-BC, CPSN, CWS
|Plastic Surgical Nursing
Volume 28 Number 4
Pages 201 - 204
Surgical site infections (SSIs) are a real risk associated with any surgical procedure. An estimated 2.6%–5% of more than 30 million operations performed per year will develop an SSI, creating a significant burden to the healthcare system. There are risk factors that influence the development of SSIs. Identifying these risk factors before elective surgery can reduce the incidence. The plastic surgical nurse can play a role in the recognition of such risk factors. The purpose of this article, Part 1 of 2, is to present known risk factors that have been identified with SSIs. The next article focuses on preventive strategies.
INCIDENCE AND IMPLICATIONS
The Centers for Disease Control and Prevention (CDC), recognizing the tremendous financial burden and impact on mortality and morbidity, developed the National Nosocomial Infections Surveillance (NNIS) system in 1970 to monitor reported trends in nosocomial infections in participating acute care hospitals in the United States. According to the NNIS, 38% of all nosocomial infections in surgical patients are SSIs. Among all hospitalized patients, 4%–16% of all nosocomial infections are SSIs. With the millions of operations performed annually, an estimated 2%–5% will develop an SSI, increasing the annual estimated cost from $130 to $845 million. The development of an SSI doubles the likelihood of post-operative death and increases the hospital stay by 7.5 days. The incidence of readmission is as high as 30%. As many as 60% of patients who develop an SSI will require an intensive care unit stay. The development of an SSI can increase the cost per episode of an estimated from $2,734 to $26,019 (http://www.ihi.org , retrieved March 24, 2008).
DIAGNOSING A SURGICAL SITE INFECTION
The CDC definition of an SSI states that infections occurring only within 30 days of surgery or within a year in the case of implants should be classified as SSIs (http://www.worldwidewounds.com , retrieved March 25, 2008). There are three classifications of SSIs: superficial incisional, deep incisional, or organ space. Signs and symptoms vary depending on location. The criteria of a superficial site infection includes purulent drainage from the incision, organisms isolated from an aseptically obtained culture of the fluid or the tissue from the incision, and at least one of the following signs or symptoms of pain or tenderness, localized swelling, erythema, or heat. Deep incisional infections are classified as those that involve deep soft tissues such as muscle or fascia. Criteria for a deep incisional infection includes purulent drainage from the incision but not from the organ or the space of the surgical site, deep incision spontaneously dehisces or is deliberately opened by the surgeon when the patient has at least one of the signs or symptoms of fever, localized pain or tenderness, an abscess, or other evidence of infection involving the incision is found on direct or by radiological examination. The severity of the infection is described as minor or major. A “minor infection” exists if there is discharge without cellulitis or deep tissue destruction. A “major infection” is described if the drainage of purulence is associated with tissue breakdown, partial or total dehiscence of the deep fascial layers of the wound, or if systemic illness is present (http://www.worldwidewounds.com , retrieved March 25, 2008). Cultures should always be obtained so that the specific organism can be treated appropriately.
TREATMENT OF SSIs
When an SSI is suspected, empiric antibiotics with broad-spectrum coverage should be initiated while awaiting culture report. Treatment then should be changed on the basis of the sensitivities. For most SSIs, the source of the pathogens is the endogenous flora of the patient's skin, mucous membranes, or hollow viscera, and the most common organism isolated is Staphylococcus aureus, often resistant to methicillin (Figure 1). Surgical debridement and washout may be necessary and topical wound care is initiated, including topical antimicrobials, on the basis of the wound characteristics. A consultation with infectious diseases should be considered for recommendations regarding length of treatment and follow-up.
|Figure 1. Incidence of surgical site infections by organisms.
Certain patient risk factors have been identified in the development of an SSI including patient characteristics. Uncontrolled diabetes has been identified as a risk factor. The findings from a study of patients who underwent coronary artery bypass graft showed a significant relationship between increasing levels of hemoglobin A1c and SSI rates (Gordon, Serkey, Barr, Cosgrove, & Potts, 1997). Also, increased glucose levels (>200 mg/dl) in the immediate post-operative period (<48 hr) were associated with increased SSI risk (Kerr et al., 1997). Stringent glucose control is essential in the prevention of SSIs in diabetic patients.
Another risk factor that has been identified is smoking. Nicotine is a vasoconstrictor and may compromise wound healing and circulation, as well as increase the workload of the heart. In a large prospective study, current cigarette smoking was an independent risk factor for sternal and/or mediastinal SSIs following cardiac surgery (Nagachinta, Stephens, Reitz, & Polk, 1987). The cessation of smoking should be a strong consideration for any elective surgery. Steroid use or other forms of immunosuppressive drugs pre-operatively have been shown to predispose to the development of an SSI. In a study of long-term steroid use in patients with Crohn's disease, SSIs developed significantly more often in patients receiving pre-operative steroids (12.5%) than in patients without steroid use (6.7%) (Post et al., 1991). Discontinuing steroid use prior to surgery must be weighed carefully with consideration for the underlying condition.
Malnutrition has been associated with post-operative nosocomial SSIs and is listed in the literature as a risk factor. A low serum albumin level is viewed as an important risk factor because it signifies a wide range of comorbid conditions that render the patient nutritionally impaired or immunocompromised (Cheadle, 2006). Olsen et al. (2008) found that malnutrition was not a risk factor in the development of a post-operative SSI in orthopedic spinal surgery. Most studies examining the impact of malnutrition have not been conducted in developing countries where severe malnutrition is more common. Because malnutrition may indicate the overall poor general health of an individual, it needs to be corrected prior to any elective surgical procedure.
“Morbid obesity,” defined as having a body mass index of more than 30 kg/m2, has been identified as a risk factor for an SSI. Olsen et al. (2008) found obesity as a risk factor in patients undergoing spinal orthopedic surgery. Obesity increases the risk substantially when the abdominal fat layer exceeds 3 cm and may be related to the need for a larger incision, decreased circulation to the fat tissue, or the technical difficulty of operating through a large fat layer (http://ahrq.gov/clinic/ptsafety/chap23 , retrieved August 14, 2008). Obesity is increasing in the United States, and the risk of SSI in this patient population can be a real problem.
Length of pre-operative stay can be a risk factor but is much less of a significant problem than in previous years. Prolonged pre-operative stay is frequently suggested as a patient characteristic associated with increased SSI risk. Length of stay often signifies the severity of illness and presence of comorbid conditions. Only life-threatening surgical procedures should be considered in this patient population. Otherwise, any elective surgery should be postponed until all underlying conditions that increase the SSI risk are addressed and corrected.
Existing infections are a risk factor in the development of an SSI. The infection should be treated before undergoing any elective surgical procedure. Colonization by methicillin-resistant Staphylococcus aureus often leads to other infections, especially in the elderly and nursing home residents (Cheadle, 2006). Staphylococcus aureus is a frequent SSI isolate. The pathogen is carried in the nares of 20%–30% of healthy humans, and it is associated with pre-operative nares carriage of the organism in surgical patients (Perl & Golub, 1998). A multivariate analysis demonstrated that such carriage was the most powerful independent risk factor for SSI following cardiothoracic operations (Kluytmans et al., 1995). Nasal swabs should be considered on individuals suspicious to be carriers such as nursing home residents and healthcare workers.
It has been reported that peri-operative transfusion of leukocyte-containing allogeneic blood components is an apparent risk factor for the development of post-operative bacterial infections, including SSIs (Vamvakas & Craven, 1998). In three of five randomized trials in patients undergoing elective colon resection for cancer, SSI risk was at least doubled in patients receiving blood transfusions (Heiss et al., 1993; Jensen, Kissmeyer-Nielsen, Wolf, & Qvist, 1996; Vamvakas, Craven, & Hibberd, 1996). Currently, there is no scientific basis for withholding necessary blood products for surgical patients as a means of either incisional or organ/space SSI risk reduction (Mangrum, Horan, Pearson, Silver, & Jarvis, 1999). In this particular situation, benefit would outweigh the risk. Other risk factors associated with SSI include peripheral vascular disease, old age, and radiation (Cheadle, 2006). Post-operative incontinence has also been found to be a risk factor (Olsen et al., 2008).
Hypothermia and hypoxia have been identified as risk factors in the development of SSIs. Maintaining a normal core temperature prevents vasoconstriction and reduced blood flow to surgical sites. Decreased blood flow to surgical sites increases the risk of SSIs by lowering the tissue oxygen tension. Hypothermia also results in reduced platelet function, shivering associated with pain and discomfort with activation of the sympathetic nervous system, and adverse cardiac events (Sesser, 1997). Kurz et al. (1996) performed a randomized controlled trial of active warming in the intra-operative care of patients undergoing elective colectomy and found a 68% reduction in the rate of wound infection in the group of patients in the normothermia group. Trauma and shock also predispose patients to SSIs because of hypoxia and hypothermia that are more likely to be present in these patients.
Operative risk factors for SSIs have also been identified. Surgical antimicrobial prophylaxis refers to a very brief course of an antimicrobial agent initiated just before an operation. Clearly, the timing is imperative to be effective in reaching a bactericidal concentration of the drug in the serum and tissues by the time the skin is incised. Also, the selection of the antimicrobial should be based on evidence from clinical trials to reduce SSIs and follow recommended guidelines. Lack of adequate surgical preparation of the skin is a risk factor. The duration of the surgical scrub and the type of skin antiseptic preparation influence the risk for SSIs. Several antiseptic agents are available for pre-operative preparation of skin at the incision site including iodophors, alcohol-containing products, and chlorhexidine gluconate. Both chlorhexidine and iodophors have broad-spectrum antimicrobial activity. In a randomized controlled study conducted by Veiga et al. (2008), staphylococcal skin colonization was significantly lower in a group of patients who showered with povidone-iodine 10% 2 hr before elective and clean plastic surgical procedures than in the group with no special shower instructions before surgery. No microorganism growth was observed on 33% of the postshower skin cultures obtained from the patients in the povidone-iodine shower group when compared with the control group that showed no reduction in skin flora. Chlorhexidine gluconate provided greater reductions in skin microflora than those achieved by povidone-iodine and also had greater residual activity after a single application (Mayhall, 1993). The scrub antiseptic may be hospital dependent, but there should be enough evidence in the literature to show its efficacy.
The length of the operation has also been identified as a risk factor for SSIs. Procedures longer than 3–4 hr increase the risk (Cheadle, 2006). Pre-operative shaving of the surgical site has also been associated with a significantly higher SSI risk than either the use of depilatory agents or no hair removal (Mishriki, Law, & Jeffery, 1990). In one study, SSI rates were 5.6% in patients who had hair removed by razor compared with 0.6% in patients who had either their hair removed by depilatory agents or no hair removal (Seropian & Reynolds, 1971). In recent years, hair entering the wound has not been considered a major source of bacteria by most surgeons and efforts to remove body hair are considered only when the hair is excessive (Cheadle, 2006). Improper adherence to asepsis and surgical technique are also risk factors and allow for contamination with exogenous microbes. Factors related to the surgical site that are likely to promote infection include the presence of hematoma, the use of epinephrine, damage to the tissues due to improper handling, and excessive use of the cautery, which results in tissue necrosis (Cheadle, 2006).
Recognizing risk factors that predispose to SSIs is important to initiate preventive strategies, correct underlying conditions, and identify those patients who are at risk. The plastic surgical nurse in collaboration with the healthcare team can play a major role in the prevention of SSIs by identifying these patients and participating in their treatment and care. It is also the responsibility of the plastic surgical nurse to be familiar with the CDC guidelines on the prevention of SSIs. Preventive strategies will be presented in the next issue.
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This department is dedicated to information pertaining to wound care. The care of wounds is an important component of the overall care of a patient, regardless of the type of surgical practice. The Wound Care Department Editor, Marcia Spear, welcomes comments and suggestions concerning specific topics, patient situations, and wound care in general. Marcia can be contacted at firstname.lastname@example.org.