A review published in June 2016 in Langenbeck’s Archives of Surgery by Donald E. Fry of the Division of Surgery at Northwestern University Feinberg School of Medicine aims to provide a comprehensive review of strategies to prevent surgical site infection (SSI) in patients undergoing colon surgery. The review focuses on four aspects of infection: etiology, pathogenesis, diagnostic monitoring, and prevention.
Infection is the leading cause of postoperative morbidity in patients undergoing elective colonic surgery. Among all elective surgeries, colon surgery infections are the most common. Infections in patients undergoing colon surgery result in higher medical costs, longer hospital stays, and are also a major cause of readmission.
Colonic microbiology
The colon absorbs most of the nutrients, water and electrolytes. This, combined with its anaerobic environment, leads to the colonization of large numbers of bacteria, and the barrier function of the colon prevents the spread of colonized bacteria. In general, the concentration of cecum bacteria is 105-106 cfu/ml, mostly Gram-negative bacteria (e.g., Escherichia coli and Klebsiella pneumoniae) (see Figure 1). As the luminal contents traveled to the distal colon and solid feces were formed, the colonizing bacteria also increased to 1010-1012 cfu/ml and gradually became anaerobic Gram-negative bacteria, with Bacteroides fragilis predominating (see Figure 1). At the same time, the number of enterococci was also increasing.
Another important point is that the concentration of bacteria covering the mucus layer from the proximal colon to the sigmoid colon and rectum is also gradually increasing. Therefore, in such a colonic environment, even with the best medical equipment, surgical interventions can result in millions of bacteria invading the local soft tissues and surgical incisions.
Figure 1 Electron microscopic view of common pathogens of SSI in post-colonic patients
Pathogenesis of SSI
Infection occurs as a result of multiple bacterial and host factors and is not solely a microbial problem.
What are the determinants of postcolonic infection?
The first and most important determinant is microbial contamination of the incisional tissue. Many studies have demonstrated that the chance of infection increases with increasing tissue bacterial density. Efforts to reduce bacterial concentrations are the most important strategy to reduce SSI. It is important to emphasize that increased bacteria in the patient’s skin and operating room environment can also interfere with the outcome of infection.
The second determinant of SSI is the virulence of the bacteria. The virulence characteristics of the individual are necessary for a much smaller number of bacteria to contaminate the incision leading to infection. The local environment of the surgical incision tissue is the third determinant of infection. The fourth determinant is the integrity of the host immune response.
Thus, the determinants of infection can be predicted by a hypothetical equation for the surgical site. Infection occurs if excessive net effect inoculation of bacteria, bacterial virulence, or hostility of the surgical site environment outweighs host immunity. Measures needed are either prophylaxis to reduce microbial action or intervention to enhance host immunity.
Figure 2 Determinants of SSI. Variables that increase the probability of infection can be offset by host genetic defense genes, and host defenses can be weakened by acquired acute and chronic diseases.
Diagnosis and monitoring of SSI
Currently, there is no standardized definition of SSI. The Centers for Disease Control and Prevention (CDC) has proposed definitions for superficial, deep, and organ/interstitial SSIs. However, a characteristic of this definition is that it is subjective; when the surgeon believes the surgical site is infected, the surgical site is infected. On the flip side: if the surgeon thinks the surgical site is not infected, then the infection is not documented. Obvious infections are easily detected, but subtle infections are often missed.
In addition to inconsistent definitions in diagnosis, the ability to monitor effectively is another major issue in the variable rates of reported SSIs. Therefore, standardized definitions and surveillance need to be established. In addition, collaboration with other institutions is essential to determine whether patients who are discharged from the hospital and readmitted to the emergency room or other institutions are infected.
Prevention of SSI
Extensive preoperative and intraoperative measures are necessary to prevent SSI. Numerous behaviors and factors can lead to infection. The use of antibiotics or the application of antiseptics to the surgical site alone will not significantly reduce SSI rates if other preventive measures are ignored.
1. Preoperative preparation
(1) Prolonged preoperative hospital stay
Several studies have suggested that prolonged preoperative hospitalization increases surgical infection complications. The prolonged preoperative hospital stay laterally reflects the complexity of the condition. It is now generally accepted that prolonged preoperative hospital stay increases infection due to colonization by hospital drug-resistant microorganisms. When hospitalized for more than 3 days, the surgeon should adjust the choice of prophylactic antibiotics to compensate for adverse colonization.
(2) Cleaning of the surgical site prior to hospitalization
Whether the use of antibacterial soap and body wash at the surgical site prior to hospitalization can prevent SSI is still an area of controversy. Instructing patients to bathe and scrub the surgical site has been shown to reduce skin flora density, but has not been consistently shown to reduce SSI rates.
(3) Skin preparation
Current evidence suggests that for most patients, body hair does not promote infection and does not need to be removed. If necessary, skin should be prepared using an electric shaver prior to the start of surgery in the operating room. Skin preparation should not be done the night before surgery, as even minor abrasions can lead to poor colonization.
(4) Pre-operative preparation of the incision
The use of antiseptics prior to surgical site incision remains controversial. It is basically considered that chlorhexidine, povidone-iodine and isopropyl alcohol are all equivalent. Adding isopropyl alcohol to chlorhexidine or povidone iodine not only enhances the bactericidal effect, but also shortens the drying time to improve the antimicrobial effect. Currently, any of these skin antiseptics or combinations can be used if applied properly and if drying is allowed prior to skin incision.
(5) Surgical films
Early surgical films failed to improve infection rates probably because the plastic did not adhere densely to the skin. Newer versions of surgical films are more flexible in their adhesion and have added bactericidal coatings to further control potential bacterial contamination. The use of surgical films showed a reduction in colonic bacterial counts in the incision, but the reduction in SSI rates was not validated.
2. Prophylactic systemic antimicrobials
Early efforts to treat with prophylactic systemic antibiotics failed because they were not administered until after the surgical procedure was completed and the incision was sutured. Antibiotics are not antimicrobially active until contamination has occurred and is present in the tissue. The use of antibiotics for systemic prophylaxis of infection after soft tissue contamination has lacked benefit.
3. Mechanical or antibiotic bowel preparation
Mechanical cleansing of the colon alone does not reduce SSI because the bacterial concentration in the mucus of the intestinal surface is not reduced. In addition, in the absence of mechanical preparation, antibiotic bowel preparation alone does not reduce SSI rates either. This is because oral antibiotics are bound to the proximal colon and cannot be spread to the fecal-filled distal colon. Complete fecal evacuation ensures that oral antibiotics reach the entire colon.
Although there are many questions regarding antibiotic bowel preparation that require further study, the current objective evidence strongly supports that oral combined with systemic antibiotics reduces the rate of SSI in elective colon surgery.
4. Intraoperative prophylaxis
(1) Technical issues
Technical management of the incision during surgery is critical for SSI prevention. Inter-incisional tissue hematoma or closure of the inter-incisional space will increase the rate of SSI. Also contributing to the same outcome is the overuse of electrocautery resulting in tissue scorch inactivation. Avoid the use of woven and non-absorbable suture materials (e.g., silk). To avoid the formation of dead space abscesses in overweight patients, the opening of the closed negative pressure drainage tube should be separated from the surgical incision. For most cases, two-way drainage should be avoided and not through the incision. Remove the drainage as soon as the objective is achieved.
(2) Incision protector
Incisional protectors are widely used in surgery. Evidence from several clinical trials also supports their use in open surgery. It is important to note that when the device is removed at the end of surgery, every effort should be made to avoid contamination of the incision.
(3) Antimicrobial sutures
Antimicrobial sutures coated with triclosan have reduced bacterial growth associated with closed incisions and hemostatic sutures. Although large multicenter randomized clinical trials are needed to further address the widespread use of this method, there is good reason to believe that antimicrobial sutures are valuable in high-risk procedures such as colectomy.
(4) Air treatment
Airborne bacteria have become a long-standing problem in surgical site contamination and subsequent infection. However, for this type of colon surgery where contamination with colon and skin colonizing bacteria can overwhelm all factors, it is difficult to imagine the extent to which any air handling or air cleaning could affect outcomes.
(5) Glycemic control
Hyperglycemia in diabetic and nondiabetic patients is associated with increased SSI. Insulin titration to lower glucose may reduce SSI rates.
(6) Temperature control
Clinical hypothermia is associated with impaired phagocytosis and coagulation dysfunction. However, the effect of hypothermia on SSI remains controversial, and further evaluation of the value of intraoperative warming efforts and levels is necessary.
(7) Administration of oxygen
Administration of oxygen enhances the host response and prevents infection of contaminated tissue. For colectomy, the administration of oxygen appears to be beneficial in reducing SSI.
(8) Incisional irrigation
Physiological saline irrigation of the incision removes blood clots and scattered incisional debris, but it has been commonly observed that it does not reduce the bacterial burden on the incisional surface. Experimental studies have demonstrated the benefit of pressure irrigation in reducing the bacterial load and actual infection in the incision. However, there are no completed clinical trials to confirm this. There is still no evidence that topical irrigation with antibiotic solutions reduces the incidence of SSI.
(9) Delayed one-stage suturing
When colonic surgery is significantly contaminated, surgeons choose to close the abdominal wall incision fascia but leave the skin and subcutaneous tissue open. The closure of a contaminated incision can be delayed until 3 to 5 days after surgery compared to cleaner incision management. The reality is that closure of heavily contaminated incisions is rarely delayed. Open incisions are rarely delayed and, conversely, are susceptible to secondary suturing. Essentially, delayed one-stage sutures result in prolonged treatment for the same amount of time as opening and closing the incision three or four days postoperatively due to infection. Published evidence suggests that the problem with delayed one-stage sutures is conflicting value and that mathematical models question their value.
5. Postoperative prophylaxis
Evidence suggests that interventions implemented after closure of the incision by colonic surgery have a limited role in effective prevention of SSI. Secondary contamination of the closed incision by a distal source of infection becomes the suspected cause, but this is more of a small probability event. If a distal source of infection is suspected of contaminating the incision through blood or lymphatic dissemination, continued postoperative systemic antibiotics to avoid infection are not justified.
In conclusion: Infections are frequent, morbid, and expensive complications of colon surgery. Knowledge of the pathogenesis and microbiology of these infections is a critical step in prevention. Improving SSI in colon resected patients requires a uniform definition of these infections and a consistent surveillance protocol in place to accurately assess these adverse events. There is a plethora of preoperative and intraoperative approaches to reduce SSI in patients undergoing colon surgery, but the timing of prevention is all prior to surgical incision closure and there is little evidence to support postoperative prophylaxis.