Project «Antibiotic Policy in Surgery 2003»
IV. Antimicrobial Prophylaxis in Surgery
Infection of the incised skin or soft tissues is a common but potentially avoidable complication of any surgical procedure. Some bacterial contamination of a surgical site is inevitable, either from the patient's own bacterial flora or from the environment, including operative team.
Risk factors for surgical site infection
The most relevant risk factors for surgical site infection (SSI) are as follows: contaminated or dirty wound class, high preoperative risk, long operations, operations with substantial blood loss, faulty aseptic technique, emergency surgery etc. Malnutrition, advanced age, obesity, diabetes mellitus, malignancy, and the use of steroids or immunosuppressive drugs are also risk factors for wound infection.
In general, risk for SSI in given patient can be calculated based on: class of operative wound, degree of preoperative risk (presence and number of co-morbidities), and duration of surgery.
Length of stay in the hospital as the risk factor for postoperative infectious complications
Bacterial contamination of skin and mucous membrane by nosocomial strains often occurs when the patient is being in the hospital. Prolonged preoperative hospital stay increases the risk for surgical site infection. Because of this, it is recommended to perform most operations and surgical procedures, whenever possible, at the day of hospitalization («same-day operations») or in ambulatory (outpatient) setting.
What is antimicrobial prophylaxis?
Antimicrobial prophylaxis in surgery is a standard of care for many surgical procedures and represents their most common use in surgery. Prophylaxis in surgery is defined as use of antimicrobial agents before contamination of infection occurred with the aim of preventing infectious complications. Surgical antimicrobial prophylaxis (AMP) is a very brief course of an antimicrobial agent initiated just before an operation begins. AMP is not an attempt to sterilize tissues, but a critically timed adjunct used to reduce the microbial burden of intra-operative contamination to a level that cannot overwhelm host defenses.
The goals of rational prophylactic administration of antibiotics to surgical patients are to:
- Reduce the incidence of surgical site infection;
- Use antibiotics in a manner that is supported by evidence of effectiveness;
- Minimize the effect of antibiotics on the patient's normal bacterial flora and host defenses;
- Minimize adverse effects;
It is important to emphasize that antibiotic prophylaxis in surgery should be regarded as one component of an effective policy for the control of hospital-acquired infection.
Indications for AMP
Prophylactic antibiotics are recommended when the risk of postoperative infection is high or with lower risk when the consequence of infection leads to significant morbidity and mortality.
A simple way to organize AMP indications is based on using the surgical wound classification, which employs descriptive case features to postoperatively grade the degree of intraoperative microbial contamination. A surgeon makes the decision to use AMP by anticipating preoperativety the surgical wound class for a given operation,
Essentially all confirmed AMP indications pertain to elective operations in which skin incisions are closed in the operating room.
Generally accepted indications are surgical interventions with high rates of infection: elective «clean-contaminated» procedures without foreign implants, and certain «contaminated» operations. AMP is indicated for all operations that entail entry into a hollow viscus under controlled conditions. Certain «clean-contaminated» operations, such as elective colon resection, low anterior resection of the rectum, and abdominoperineal resection of the rectum, also require an additional preoperative protective maneuver called «preparation of the colon», to empty the bowel of its contents and to reduce the levels of live microorganisms. This maneuver includes the administration of enemas and cathartic agents followed by the oral administration of nonabsorbable antimicrobial agents in divided doses the day before the operation (see also: Selective decontamination of the digestive tract).
AMP is sometimes indicated for operations that entail incisions through normal tissue and in which no viscus is entered and no inflammation or infection is encountered. Two well-recognized AMP indications for such clean operations are:
- When any intravascular prosthetic material (e.g. coronary artery bypass operations, vascular bypasses in the leg with vein grafts) or a prosthetic joint will be inserted;
- For any operation in which an incisional or organ/space SSI would pose catastrophic risk (e.g. neurosurgery, heart surgery).
Emergency «clean» operations and emergency cesarean section, which is a «clean-contaminated» operations are also indication for administration of prophylactic antibiotics. Other emergency operations with contaminated or dirty wounds require antibiotic therapy rather than prophylaxis.
By definition, AMP is not indicated for an operation classified as contaminated or dirty. In such operations, patients are frequently receiving therapeutic antimicrobial agents perioperatively for established surgical infections.
The final decision regarding the benefits and risks of prophylaxis for an individual patient will depend on:
- Patient's risk of surgical site infection
- Potential severity of the consequences of surgical site infection
- Effectiveness of prophylaxis in that operation
- Consequences of prophylaxis for that patient (e.g. increased risk of antibiotic-associated colitis)
When antibiotic prophylaxis is not indicated?
Prophylactic systemic antibiotics are clearly not indicated for most patients undergoing «clean» surgical operations (exception for mentioned above ones), in which no obvious bacterial contamination or insertion of a foreign body has occurred. In general, prophylactic antibiotics are not indicated when the infection rate is very low (in the range of 1% or less) and/or when the morbidity of a surgical site infection is very low, such as in removal of small skin lesions.
Choice of prophylactic antibiotics
The choice of an antibiotic for prophylaxis depends on:
- Type of the surgical procedure;
- organism that must be covered;
- pharmacokinetic properties;
- safety profile;
- results of properly designed clinical trials.
The chosen antibiotics must reflect local, disease-specific information about the common pathogens and their antimicrobial susceptibility.
A single drug should be used, whenever possible.
The following antibiotics are suitable for antibiotic prophylaxis:
- for most «clean» and «clean-contaminated» operations - cephalosporin I (cefazolin) or II
- for «contaminated» operations:
- up to distal ileum - cephalosporin I or II (cefazolin, cefuroxime);
- from distal ileum, biliary tract, gynecology and ear, nose and throat surgery: cephalosporin I or II + metronidazole, extended-spectrum beta-lactam/beta-lactamase inhibitor (ampicillin/sulbactam, amoxicillin/clavulanic acid).
The routine use of vancomycin in AMP is not recommended for any kind of operation. However, vancomycin may be the AMP agent of choice in certain institutions with high predominance of methicillin-resistant strains of S.aureus.
Third-generation cephalosporins are more costly and promote the emergence of resistant strains. In general, they should not be used for routine prophylaxis in surgery.
Dosage, route and timing of administration
The single dose of antibiotic for prophylactic use is, in most circumstances, the same as would be used therapeutically.
Prophylactic antibiotics should be administered intravenously. Fluid replacement bags should not be primed with prophylactic antibiotics because of the potential risk of contamination and calculation errors.
The infusion of initial dose of antimicrobial agent should be started preoperatively so that a bactericidial concentration of the drug is established in serum and tissues by the time the skin is incised. The best timing for the prophylactic antibiotic is the induction of anaesthesia, i.e. prior to tissue contamination, so that the highest tissue and serum concentrations are maintained throughout the operation and until, at most, a few hours after the incision is closed in the operating room. It is unnecessary and may be detrimental to start them more than 1 hour preoperatively, and it is unnecessary to give them after the wound is closed and the patient leaves the operating room.
As long as adequate serum drug levels are maintained during the operation, a single dose is often sufficient. In the case of massive hemorrhage, or whenever the duration of an operation exceeds 3 hours, a repeat dose should be given every two to three half-lives. It is almost never indicated to give prophylactic antibiotic coverage for more than 24 hours for a planned operation.
There are a few exceptions to these basic principles. With respect to dosing, it has been demonstrated that larger doses of AMP agents are necessary to achieve optimum effect in morbidly obese patients. Some authors recommend that large patients (>90 kg) receive a double dose of prophylactic antibiotic. With respect to timing, an exception occurs for patients undergoing cesarean section, in whom AMP is indicated: the initial dose is administered immediately after the umbilical cord is clamped. For any operation in which a tourniquet will be used it is mandatory to have the entire dose of prophylactic antibiotic infused before the tourniquet is inflated.
Can antimicrobial prophylaxis substitute for surgical technique?
Surgical antimicrobial prophylaxis is an adjunct, not an alternative to good surgical technique, using established surgical principles, or to asepsis and antisepsis and they should be used with sound principles. Its indiscriminate or general use is not in the best interest of the patient Prophylactic antibiotics should not be used as a remedy for poor aseptic technique in clean operations. The use of foreign bodies including sutures and drains, lack of accurate approximation of tissues, strangulation of tissue with sutures that are too tight, and the presence of any dead tissue, hematomas, or seromas all increase the risk of infection. Fortunately, most of these factors can be minimized by good surgical technique.
In what cases is antibiotic prophylaxis ineffective?
Prophylactic antibiotic therapy is generally ineffective in clinical situations, in which continuing contamination is likely to occur. Examples are as follows:
- In patients with tracheostomies or tracheal intubation to prevent pulmonary infections;
- In patients with indwelling urinary catheters;
- In patients with indwelling central venous lines;
- In most open wounds, including burn wounds.
Is postoperative fever always linked to the infection?
Wound infections and, more rarely, abdominal abscesses are usually not identifiable until the 5 to 10 postoperative day or even later, although these patients often have fever beginning early in the postoperative course. Fever is the most common sign of developed infection, but there are a lot of non-infective causes of postoperative fever.
An elevated temperature often occurs during routine observation of postoperative patients but does not necessarily signal a serious complication or necessarily warrant an extensive diagnostic work-up. A specific cause is identified in less than 20% of patients with pyrexia during the initial 24 hours; in the remainder, it may be regarded as a normal response to surgical trauma. Fever that begins within 24 hours after operation usually suggests atelectasis. Transfusion or drug reactions may induce fever in the early postoperative period. A hematoma may elicit a mild febrile response, or fever may originate from inflammation around an intravenous catheter after the administration of irritant fluids or drugs. Deep vein thrombosis, with the risk of pulmonary embolism, may be associated with mild pyrexia and usually presents after the fifth postoperative day.
Surveillance of SSI
Surveillance of SSI with feedback of appropriate data to surgeons has been shown to be an important component of strategies to reduce SSI risk. A successful surveillance program includes the use of epidemiologically sound infection definitions (criteria for defining of SSI) and effective surveillance methods, stratification of SSI rates according to risk factors associated with SSI development, and data feedback.
Two methods, alone or together, may be used to identify inpatients with SSIs: (1) direct observation of the surgical site by the surgeon, trained nurse surveyor, or infection control personnel; and (2) indirect detection by infection control personnel through review of laboratory reports, patient records, and discussions with primary care providers. The surgical literature suggests that direct observation of surgical sites is the most accurate method to detect SSI. Indirect SSI detection can readily be performed by infection control personnel during surveillance rounds.
An effective SSI surveillance program must be operational, with careful and timely culturing of SSI isolates to determine species and AMP agent susceptibilities.
It is a valuable exercise to categorize surgical site infections into those that are potentially preventable and those that are apparently unavoidable. A potentially preventable infection is one in which it can be demonstrated by investigation of the circumstances that one or more measures which are known to reduce infection risk and that could have been carried out for this patient were not performed. An apparently unavoidable infection is one where all known appropriate preventive measures were carried out. By identifying potentially preventable infections and then providing this information back to the surgical team, and by investigating how or why preventive measures were not carried out, one can identify the causes of these errors and devise strategies to avoid them in the future. A program such as this should be able, eventually to achieve a goal of zero potentially preventable infections.