Definition of Surgical Site Infection

SSI has been defined by the CDC. Identification of an SSI is based on physical exam findings of localized pain/tenderness, swelling, erythema, heat, or purulent drainage, as well as cultures and radiologic findings ( Fig. 86.1 ). Superficial SSIs involve the skin and subcutaneous tissues, while deep SSIs involve the fascia and muscle layers. Superficial and deep SSIs occurring in the absence of an implantable device are defined as occurring within 30 days after the operation. When a device is implanted, a deep SSI is defined as occurring within 1 year post implant.

A surgical site infection of an intrathecal pump abdominal incision.

Pathogens Associated With Surgical Site Infections

Organisms causing SSIs can be categorized as coming from an endogenous or exogenous source. The most common pathogens in descending order are Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus, Escherichia coli, and Pseudomonas aeruginosa. The most common source of infection is from the patient’s own flora. It has been shown that pathogenic S. aureus isolated from an infected wound matches cultures from the patient’s nares 80%–85% of the time.

Scope of Interventional Pain Procedures and Risk of Infection

Interventional pain procedures and surgeries vary considerably based on the pain syndrome being treated, practitioner technique, and surgical theater environment. The invasiveness of procedures varies, and thus different infection control practices must be considered. Recommendations for the prevention of SSIs have been published by the CDC, NICE, and SCIP ( Table 86.3 ).

Patient Risk Factors

Physicians should identify patient-related risk factors prior to performing a procedure, and efforts should be made to correct any modifiable risk factors ( Table 86.4 ). Postmarket surveillance data on SCS and IDDS implants revealed 38% and 70% of patients with SCS and IDDS infections, respectively, had a medical comorbidity that increased their risk of infections. Smoking has been associated with an increased risk of SCS infections, likely secondary to the development of microvascular disease, leading to tissue ischemia and poor wound healing. Although the biological effects of cancer and chemotherapeutic drugs can weaken host immunity, a retrospective study demonstrated that implantable pain therapies can still be utilized in cancer patients without significantly increasing the risk of SSI when appropriate infection control measures are taken.

Preoperatively, a thorough history and physical exam should be performed to identify patient risk factors. Many measures can be taken to reduce the risk of SSIs, such as glucose optimization, tobacco cessation (for at least 4 weeks), optimization of viral load in HIV patients, minimizing/avoiding perioperative steroids, and treatment of remote infections (e.g., urinary tract). Nonmodifiable risk factors need to be documented, and a discussion with the patient regarding the associated increased risk of infection should occur prior to the pain intervention.

Staphylococcus Aureus Carriers

Staphylococcus aureus is the leading cause of SSIs, accounting for approximately 20% of all SSIs, 30% of implantable cardioverter-defibrillator (ICD) implants, and 60% of all prosthetic joint infections. Greater than 80% of nosocomial S. aureus infections are endogenous, and the number of cases of methicillin-resistant S. aureus (MRSA) SSIs is increasing. S. aureus nasal colonization rates have been reported from 20% to 80%, depending on the population studied.

Methicillin-sensitive S. aureus (MSSA) and MRSA carriers have been shown to have a significantly higher risk for developing an SSI (two to nine times higher). Therefore identification of carriers followed by decolonization protocols is critical in reducing SSI rates and has been recommended as an infection control measure. Decolonization of S. aureus carriers has also been shown to be a cost-effective treatment.

Decolonization protocols have described the application of mupirocin 2% nasal ointment applied twice daily, combined with chlorhexidine gluconate soap total-body washes daily for a duration of 5 days immediately preceding surgery. Utilization of decolonization protocols in individuals that are colonized reduces the rate of postoperative infections by greater than 50%. No data exist to support the use of routine decolonization protocols in patients who do not test positive for S. aureus colonization.

Antibiotic Prophylaxis

Preoperative antibiotic prophylaxis has been shown to significantly reduce the risk of SSIs, and the incidence of wound infection by approximately 50%, regardless of the type of surgery. Antibiotic prophylaxis ( Table 86.5 ) is recommended for implantable pain therapies (i.e., trials and implant stages). Proper antibiotic selection, route of administration, dosing, and timing are critical, as suboptimal implementation has been found to increase the risk of infection twofold to sixfold. Cephalosporins are recommended as first-line agents. If a patient has a β-lactam allergy, clindamycin or vancomycin are alternative antibiotics. In individuals colonized with MRSA or at high risk for MRSA (e.g., institutions that have a high rate of MRSA infections), vancomycin is recommended.

In order for antibiotic prophylaxis to be effective, minimum inhibitory concentrations (MIC) must be reached prior to surgical incision and maintained throughout the duration of the surgery. Preoperative antibiotics should be administered intravenously (IV) prior to incision time (30–60 minutes prior to incision or 120 minutes of incision for vancomycin). Cefmetazole 2 g IV administered immediately prior, 15 minutes prior, and 60 minutes prior to incision all showed MIC90 in blood and tissue samples throughout surgical procedures, lasting on average 2.1–2.4 hours. In order to reach MIC, weight-based dosing is needed. Weight-based dosing (2 g of cefazolin in morbidly obese patients) prior to gastroplasty was shown to decrease SSI rates to 5.6%, compared with 16.5% when 1 g of cefazolin was administered.

The kidneys excrete the majority of antibiotics used for surgical prophylaxis. The exception is clindamycin, which is primarily excreted via the biliary system. Therefore creatinine clearance must be taken into account prior to antibiotic dosing. Redosing is needed when the duration of surgery is longer than two half-lives of the administered antibiotic (see Table 86.5 ).

The continuation of antibiotics in the postoperative period is not recommended beyond 24 hours for clean surgical wounds. Prolonged antibiotic use in the postoperative period does not improve outcomes and may result in poorer outcomes. Specifically, the continuation of antibiotics in the postoperative period has been associated with delayed normalization of body temperature and elevation of the C-reactive protein (CRP) level. The SCIP guidelines recommend the discontinuation of antibiotics within 24 hours of surgery.

There are no recommendations or evidence for the use of antibiotic prophylaxis in the majority of routine interventional pain procedures (i.e., epidural steroid injections, facet blocks); however, for those that are considered higher risk for infection (i.e., indwelling catheters, and device trials/implants), antibiotic prophylaxis is recommended. For discography and other intradiscal procedures, controversy exists on the need for IV and/or intradiscal antibiotic administration. Intravenous antibiotics do not reliably achieve adequate intradiscal concentrations. Therefore intradiscal antibiotics have been recommended. However, ex vivo studies examining the effects of high antibiotic concentrations on cultured human intervertebral disc annular cells demonstrated deleterious effects on cell survival, cell proliferation, and metabolic rates. Bogduk et al. demonstrated with pooled data that the prevalence of discitis when antibiotic medications are not used is 0.24% (95% confidence intervals: 0.11%–0.37%), which is higher than the reported overall incidence of 0.15% per patient.

Surgical Hand-Washing

Appropriate surgical scrubbing of the hands and forearms is a CDC Category IB and NICE recommendation. Commercially available antiseptic solutions in the United States contain alcohol, chlorhexidine, and/or povidone-iodine. There is evidence that chlorhexidine-based scrubs reduce the number of colony-forming units compared with povidone-iodine scrubs; however, the data supporting its clinical relevance are lacking. The duration of the surgical scrub appears to be the most important factor to ensure adequate hand hygiene and limit bacterial counts. Surgical hand-washing lasting between 2 and 5 minutes results in statistically fewer CFUs when compared with hand-washing techniques of lesser duration.

The removal of hand and wrist jewelry prior to surgical scrub is a CDC Category II and NICE recommendation, as well as an American Society of Regional Anesthesia and Pain Medicine (ASRA) recommendation when performing regional anesthesia. The presence of hand jewelry increases bacterial counts on the hands of health care workers, even after hand-washing.

The method of hand hygiene required to minimize the risk of infections associated with interventional pain procedures has not been clearly established. Hebl recommended thorough hand-washing with an alcohol-based antiseptic prior to performing regional anesthetic techniques, but did not recommend a specific method or duration. For implantable devices and indwelling catheters, a full surgical scrub is recommended.

Appropriate Hair Removal

The CDC Category IA and NICE do not recommend routine removal of hair to reduce the risk of SSI, and if hair is removed clippers are the method of choice. Timing and method of hair removal appear to be the most important factors to consider. A meta-analysis looking at hair removal techniques concluded that there is no difference in SSI rates when comparing no hair removal to hair removal with chemical or clipper methods; however, shaving methods do increase the risk of SSIs. Both clipping and shaving hair 24 hours or more before an operation significantly increases the risk of SSI. There are no data to evaluate the efficacy of hair removal strategies prior to interventional pain procedures.