Surgical Site Infections
Epidemiology, Definition & Classification
Surgical site infections are defined as infections occurring within 30 days after a surgical operation (or within 1 year if an implant is left in place after the procedure) that affect either the incision or tissue deep into the operation site. A wound is considered infected if it meets any of the CDC definitions, including the isolation of pathogens from an aseptically obtained culture of fluid or tissue from the wound; purulent drainage from the incision, with or without laboratory confirmation of infection; local signs and symptoms of infection such as erythema and warmth; and diagnosis of wound infection by the surgeon.
Surgical site infections may be superficial (those involving only the skin or subcutaneous tissue) or deep incisional infections (those involving deep soft tissues of an incision) or infections involving organs or body spaces (Figure 1). Organ/space SSIs are associated with both higher mortality rate and higher costs than superficial SSIs.
Classification of surgical site infections according to CDC National Nosocomial Surveillance System.
SSI: Surgical site infection.
Reproduced from .
According to the CDC, SSIs are the second most frequently reported nosocomial infections and account for 22% of all healthcare-associated infections.[13,16] Among surgical patients, SSIs are the most common nosocomial infection, accounting for 38% of healthcare-associated infections. It is estimated that SSIs develop in 2–5% of the 16 million patients undergoing surgical procedures in the USA each year (i.e., one out of every 24 patients who have inpatient surgery in the USA develops a postoperative SSI).
Surgical site infections in the general population are associated with a two- to three-fold increased risk of death, and a 60% increased risk of requiring a postoperative intensive care unit stay. Length of hospital stay is increased by 7–12 days, the patient is five-times more likely to require readmission, and direct healthcare costs are increased by at least US$5000.
The incidence of SSIs with open bariatric surgeries can be as high as 16%. At our institution (Detroit Medical Center, MI, USA) the SSI rate was 12% among the 751 patients who underwent open RYGBs. However, the incidence of SSIs has decreased with the introduction of laparoscopic procedures with rates of SSI incidence following this approach at 4%,[20–22] probably due to smaller incisions, shorter hospital stay and minimal blood loss, compared with open procedures.
Obesity as a Risk Factor for SSIs
Several studies in the general surgical population have reported obesity to be an independent risk factor for SSIs and for associated morbidity and mortality.[10,23,24] A prospective study by Dindo et al. found that SSIs were significantly more common in the obese population (4% in obese patients vs 3% in nonobese patients; p = 0.03). Interestingly, wound infection rates and severity were similar in morbidly obese patients who underwent bariatric surgery compared with nonbariatric abdominal operations (15 and 16%).
Obesity increases the risk for SSI by several mechanisms. The primary defence against pathogens is oxidative killing by neutrophils, which is critically dependent on tissue oxygen tension. Hence, the incidence of surgical wound infections is directly related to tissue perfusion and oxygenation. Obese patients have decreased tissue oxygen tension at, and near, the incision site, which increases the risk for SSI. Fleischmann et al. demonstrated that tissue oxygenation is also impaired in obese patients undergoing laparoscopic surgery as a result of hemodynamic compromise caused by pneumoperitoneum.
Other proposed mechanisms for increased SSI risks in obese patients are decreased serum and tissue concentrations of prophylactic antibiotics and increased rates of preoperative hyperglycemia.[27,28] In addition, obese patients have an increased frequency of other comorbid conditions, such as diabetes mellitus that increase the risk for SSIs. In addition, the perioperative skin preparation of obese patients, as well as surgical closure, can be particularly challenging compared with nonobese patients.
Risk Factors for SSIs following Bariatric Surgery
Although the risk factors for SSIs have been well described for various types of surgical procedures, scant data exist describing risk factors for SSIs following bariatric surgery.[17,18] Christou et al. conducted a retrospective review addressing the incidence of and risk factors for SSI in 269 patients undergoing open bariatric surgery. According to their risk-stratification analysis, 10.9 (4%) SSIs were expected, but 54 (20%) were observed. The authors identified the use of epidural analgesia and delay in the appropriate timing of prophylactic antibiotics to be associated with a higher risk of SSI. Interestingly, their study found a high correlation between SSI and development of post-incisional hernia, another common complication following surgery in obese patients.
At the Detroit Medical Center, our group performed a case–cohort study during a 2-year study period (2006–2008) to determine the risk factors for SSI following open RYGB surgical procedures. The SSI rate among the 751 RYGBs performed was 12% (n = 91). A total of 65 SSIs were categorized as superficial, 18 as deep incisional and eight as organ/space. Bivariate predictors of SSIs included morbid obesity (defined by the authors as BMI ≥50), asthma, smoking, sleep apnea, increased duration of surgery, presence of urinary incontinence in the preoperative setting and needing assistance with ambulation in the preoperative setting. In multivariate analysis, Type 2 diabetes, morbid obesity (BMI ≥50), preoperative urinary incontinence and sleep apnea were each associated with an approximate twofold increase in SSI risk. SSI following RYGB was associated with an increased risk for emergency department visits for all causes, hospital re-admissions, outpatient procedures and 30-day mortality.
Most SSIs following bariatric surgery occur within the first 2–3 weeks of surgery. The most common source of pathogens causing SSIs post-gastrointestinal surgeries is endogenous patient flora (including staphylococcal and streptococcal species) and flora of the gastrointestinal tract (including aerobic and anaerobic Gram-negative bacilli). As is similar with other gastrointestinal surgeries, SSI following bariatric surgery can be polymicrobial. The most common organisms causing SSI following bariatric surgery include staphylococcal species such as Staphylococcus aureus and coagulase-negative staphylococci. At our institution, of the 91 SSIs in our study, the most commonly isolated bacteria were streptococci (n = 27), Enterococcus spp. (n = 9), coagulase-negative staphylococci (n = 9), Enterobacteriaceae (n = 5), S. aureus (n = 4) and Eikenellaspp. (n = 3). Anaerobic cultures were sent from the operating room in 25 cases and in 15 cases (60%), anaerobes were recovered. The most common anaerobe isolated was Prevotella (n = 10), followed by Peptostreptococcus (n = 5, including one case of bacteremia), Bacteroides (n = 1) and Veillonella (n = 1).
Anastomotic Leak & Intra-abdominal Sepsis following Bariatric Surgery
Anastomotic leak occurs in up to 5.8% of bariatric surgeries and is considered one of the most life-threatening complications of bariatric surgery. It is reported to be even more common than pulmonary embolism[30,31] and can lead to peritonitis, severe intra-abdominal sepsis, intensive-care unit admission and high mortality.
Intra-abdominal sepsis, a complication often associated with anastomatic leak, is an important, life-threatening complication of any abdominal surgery. Early recognition of intra-abdominal sepsis can be a challenge in obese patients owing to the misleading absence of abdominal signs due to large masses of subcutaneous abdominal tissue. A study by Kermarrec et al. reported that respiratory distress and tachycardia are early markers of abdominal sepsis in bariatric surgery patients. Other investigators have demonstrated upper gastrointestinal studies to be very predictive of early leak diagnoses. In patients with an anastomotic leak and severe abdominal infection, delaying surgery can lead to increased mortality; hence early re-exploration in order to obtain source control of the leak (within 48 h of index surgery) should be practiced. Sapala et al. described a method for 'leak prophylaxis' in their prospective study including 738 open RYGB surgeries and found that application of fibrin sealant at the anastomotic site can prevent leaks.
Port Site Infections in LAGB
Laparoscopic adjustable gastric banding is a very effective type of bariatric surgery performed in the modern era.
The most common type of infection associated with LAGB is infection of the implanted subcutaneous access port with an incidence ranging from 0.3 to 9%.[37,38] The diagnosis of a port infection can be made as a clinical diagnosis or following upper endoscopy. Upper endoscopy can also rule out band erosion. Isolated port infections are managed by removing the port and implanting a new port once the infection has cleared. Even though port infection is considered a relatively minor complication of LAGB, it often necessitates re-operation at the port site or at the level of the band. To circumvent this complication, Fabry et al. came up with a technique that ensures port stability by using a larger surface area for attachment of the port to the fascia.
Expert Rev Pharmacoeconomics Outcomes Res. 2010;10(3):317-328. © 2010 Expert Reviews Ltd.
Cite this: Preventing Surgical Site Infections after Bariatric Surgery: Value of Perioperative Antibiotic Regimens - Medscape - Jun 01, 2010.