Surgical Site Infections and Their Management

Fig. 10.1

Cross section of abdominal wall depicting the CDC classification of surgical site infection (Adapted from Horan et al. [2])

Table 10.1

Criteria for defining a surgical site infection (NHSN, 2008)

Superficial incisional SSI

Infection occurs within 30 days after the operation and infection involves only skin or subcutaneous tissue of the incision and at least one of the following:

1. Purulent drainage from the superficial incision.

2. Organisms isolated from an aseptically obtained culture of fluid or tissue from the superficial incision.

3. At least one of the following signs or symptoms of infection (pain or tenderness, localized swelling, redness, or heat) and superficial incision is deliberately opened by surgeon, and is culture-positive or is not cultured.

4. Diagnosis of superficial incisional SSI is made by the surgeon or attending physician.

Deep incisional SSI

Infection occurs within 30 days after the operation if no implant is left in place or within 1 year if an implant is in place and the infection appears to be related to the operative procedure, involves deep soft tissues (e.g., fascial and muscle layers) of the incision, and the patient has at least one of the following:

1. Purulent drainage from the deep incision but not from the organ/space component of the surgical site.

2. A deep incision spontaneously dehisces or is deliberately opened by a surgeon and is culture-positive or not cultured and the patient has at least one of the following signs or symptoms: temperature >38 °C or localized pain or tenderness (a culture-negative finding does not meet this criterion).

3. An abscess or other evidence of infection involving the deep incision is found on direct examination, during reoperation, or by histopathologic or radiologic examination.

4. Diagnosis of a deep incisional SSI is made by a surgeon or attending physician.

Note:

An infection that involves both superficial and deep incision sites should be reported as a deep incisional SSI

An organ/space SSI that drains through the incision should be reported as a deep incisional SSI

Organ/Space SSI

Infection involves any part of the body, excluding the skin incision, fascia, or muscle layers, that is opened or manipulated during the operative procedure. Specific sites are assigned to organ/space SSI to further identify the location of the infection (e.g., endocarditis, endometritis, mediastinitis, vaginal cuff, and osteomyelitis). Organ/space SSI must meet the following criteria:

1. Infection occurs within 30 days after the operative procedure if no implant is in place or within 1 year if implant is in place and the infection appears to be related to the operative procedure.

2. Infection involves any part of the body, excluding the skin incision, fascia, or muscle layers, that is opened or manipulated during the operative procedure, and the patient has at least one of the following: purulent drainage from a drain that is placed through a stab wound into the organ/space, organisms isolated from an aseptically obtained culture of fluid or tissue in the organ/space, an abscess or other evidence of infection involving the organ/space that is found on direct examination, during reoperation, or by histopathologic or radiologic examination, and diagnosis of an organ/space SSI by a surgeon or attending physician

Adapted from Horan et al. [3]

10.3 Epidemiology and Pathogenesis

We are constantly exposed regularly to microorganisms in our environment; yet, infection is uncommon in healthy individuals with intact host defenses. These microbes populate our skin and mucous membranes as well as some organs but usually exist in a commensal relationship with humans as their hosts.

Microbial contamination of the surgical site is a necessary precursor for SSI. This happens most commonly when an incision is exposed to the patient’s exogenous or endogenous bacterial flora. Exposure can also occur from healthcare personnel, the operating environment, or from contaminated equipment or instruments. Less commonly, the surgical site can be contaminated by hematogenous seeding from a remote site of infection.

Infection occurs when there is an imbalance among the degree of contamination, host defenses, and the environment. Contamination is influenced by inoculum size and virulence of the involved organisms. Examples of local host factors include desiccation or tissue damage at the incision, and a hematoma or seroma at the surgical site. There also are a variety of systemic, environmental, and treatment-related factors associated with an increased propensity to develop an SSI (Table 10.2).

Table 10.2

Risk factors for the development of surgical site infection

Local factors

Damage from electrocautery

Degree of contamination

Duration of expose to contamination

Hematoma or seroma

Poor operative technique

Prior irradiation of the site

Skin disease at or near the incision

Tissue desiccation

Tissue hypoxemia

Systemic factors

Abnormalities of coagulation

Advanced age

Altered immune response

Anemia

Chronic liver disease

Chronic inflammation

Chronic renal disease

Corticosteroid therapy

Diabetes mellitus

Hypoalbuminemia

Hypovolemic shock

Hypoxemia

Infection at a remote body site

Malnutrition

Obesity

Organ dysfunction

Peripheral vascular disease

Smoking

Environmental factors

Contamination from personnel

Inadequate disinfection/sterilization

Inadequate skin antisepsis

Preoperative hair removal

Preoperative skin preparation

Substandard operating room ventilation

Treatment factors

Drains

Hypothermia

Prolonged operative time

Prolonged preoperative hospitalization

The risk of SSI is highly dependent on the degree of contamination and is markedly increased when the inoculum is >10⁷ microorganisms per gram of tissue. However, a much lower dose of contaminating microorganisms can produce infection when foreign material is present or if the host or local environment is compromised by other factors or conditions [4].

10.4 Risk Factors

There are a number of risk factors that have been identified to influence the occurrence of SSI (Table 10.2). Understanding the contribution of each of these elements to the occurrence of SSI encourages targeted interventions aimed at reducing the incidence of infection. It is useful to explore some of the risk factors that are potentially controllable in some detail.

Increased serum glucose (>200 mg/dL) in the postoperative period has been associated with a greater incidence of SSI, particularly among patients undergoing cardiac surgery [5]. It has also been suggested that chronic glucose control as assessed by serum hemoglobin A1c levels may influence infection risk [6]. The independent contribution of diabetes mellitus to SSI risk is difficult to discern, since most studies do not control for confounding factors.

Nicotine use delays primary wound healing and may increase the risk of SSI via this mechanism. In a large prospective study, current smoking of cigarettes was an independent risk factor for sternal and/or mediastinal deep SSI following cardiac surgery [7]. Others have corroborated cigarette smoking as an important risk factor [8].

Although individual comorbid conditions may have some impact on infection risk, results from the NNIS have demonstrated that the overall predictive risk of SSI can be assessed by using the American Society of Anesthesiologists (ASA) physical status score, duration of operation, and incision classification (Tables 10.3 and 10.4). Assigning one point each when the ASA physical status score is ≥3, duration of operation exceeds the 75th percentile for the particular operation, and incision site (wound) class is contaminated or dirty, provides a reasonably accurate prediction for the risk of SSI [9]. This model is most accurate to predict the occurrence of superficial SSI. There may be different risk factors for deep and organ/space SSI [10].

Table 10.3

American Society of Anesthesiology (ASA) physical status score

ASA 1- A normal healthy patient

ASA 2- A patient with mild to moderate systemic disturbance that does not result in functional limitations. Examples: Hypertension, diabetes mellitus, chronic bronchitis, morbid obesity, and extremes of age

ASA 3- A patient with severe systemic disturbance that may result in functional limitations but is not incapacitating. Examples: Poorly controlled hypertension, diabetes mellitus with vascular complications, angina pectoris, prior myocardial infarction, and pulmonary disease that limits activity

ASA 4- A patient with a severe systemic disturbance that is life threatening with or without the planned procedure. Examples: Congestive heart failure, unstable angina pectoris, advanced pulmonary, and renal or hepatic dysfunction

ASA 5- A moribund patient who is not expected to survive with or without the operative procedure. Examples: Ruptured abdominal aortic aneurysm, pulmonary embolism, and head injury with increased intracranial pressure

Table 10.4

Surgical wound classification

Clean: An operative wound in which no inflammation or infection is encountered and the respiratory, alimentary, genital, or uninfected urinary tracts are not entered. In addition, clean wounds are primarily closed with or without closed drainage. Operative incisional wounds that follow nonpenetrating (blunt) trauma should be included in this category if they otherwise meet the criteria

Clean-contaminated: An operative wound in which the respiratory, alimentary, genital, or urinary tracts are entered under controlled conditions and without unusual contamination. Specifically, operations involving the biliary tract, appendix, vagina, and oropharynx are included in this category, provided no evidence of infection or major break in technique is encountered

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