Antibiotics administered prior to the contamination of previously sterile tissues or fluids are considered prophylactic. The goal of prophylactic antibiotics is to prevent an infection from developing.
Presumptive antibiotic therapy is administered when an infection is suspected but not yet proven. Therapeutic antibiotics are required for established infection.
Surgical-site infections (SSIs) are classified as either incisional (eg, cellulitis of the incision site) or involving an organ or space (eg, with meningitis). Incisional SSIs may be superficial (skin or subcutaneous tissue) or deep (fascial and muscle layers). Both types, by definition, occur by postoperative day 30. This period extends to 1 year in the case of deep infection, associated with prosthesis implantation.
RISK FACTORS FOR SURGICAL WOUND INFECTION
The traditional classification system developed by the National Research Council (NRC) stratifying surgical procedures by infection risk is reproduced in Table 48–1. The NRC wound classification for a specific procedure is determined intraoperatively and is the primary determinant of whether antibiotic prophylaxis is warranted.
The Study on the Efficacy of Nosocomial Infection Control (SENIC) analyzed more than 100,000 surgery cases and identified abdominal operations, operations lasting more than 2 hours, contaminated or dirty procedures, and more than three underlying medical diagnoses as factors associated with an increased incidence of SSI. When the NRC classification described in Table 48–1 was stratified by the number of SENIC risk factors present, the infection rates varied by as much as a factor of 15 within the same operative category.
The SENIC risk assessment technique has been modified to include the American Society of Anesthesiologists preoperative assessment score (Table 48–2). An American Society of Anesthesiologists score greater than or equal to three was associated with increased SSI risk.
TABLE 48–1National Research Council Wound Classification, Risk of Surgical Site Infection, and Indication for Antibiotics |Favorite Table|Download (.pdf) TABLE 48–1 National Research Council Wound Classification, Risk of Surgical Site Infection, and Indication for Antibiotics
| ||SSI Rate (%) || || |
|Classification ||Preoperative Antibiotics ||No Preoperative Antibiotics ||Criteria ||Antibiotics |
|Clean ||5.1 ||0.8 ||No acute inflammation or transection of GI, oropharyngeal, genitourinary, biliary, or respiratory tracts; elective case, no technique break ||Not indicated unless high-risk procedurea |
|Clean–contaminated ||10.1 ||1.3 ||Controlled opening of aforementioned tracts with minimal spillage/minor technique break; clean procedures performed emergently or with major technique breaks ||Prophylactic antibiotics indicated |
|Contaminated ||21.9 ||10.2 ||Acute, nonpurulent inflammation present; major spillage/technique break during clean–contaminated procedure ||Prophylactic antibiotics indicated |
|Dirty ||N/A ||N/A ||Obvious preexisting infection present (abscess, pus, or necrotic tissue present) ||Therapeutic antibiotics required |
TABLE 48–2Surgical Site Infection Incidence (%) Stratified by NRC Wound Classification and SENIC Risk Factorsa
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