5 things you should know about antibiotic prophylaxis

We can define surgical site infection (SSI) as that infection that occurs in the wound created by an invasive surgical procedure.

Surgical site infections are one of the most important causes of healthcare-associated infections and are associated with considerable morbidity. It has been reported that over one-third of postoperative deaths are related, at least in part to SSI.

We can describe three levels:

1. Superficial incisional, affecting the skin and subcutaneous tissue. These infections can be indicated by localised signs such as redness, pain, heat or swelling at the site of the incision or by the drainage of pus.

2. Deep incisional, affecting the fascial and muscle layers. These infections can be indicated by the presence of pus or an abscess, fever with wound tenderness, or a separation of the edges of the incision exposing the deeper tissues.

3. Organ or space infection, which involves any part of the anatomy other than the incision that is opened or manipulated during the surgical procedure, for example a joint or the peritoneum. These infections can be indicated by the drainage of pus or the formation of an abscess detected by histopathological or radiological examination or during re-operation. Organ infection is not included within the scope of this guideline.

Common principles of antimicrobial agents

Ideally, an antimicrobial agent for surgical prophylaxis should prevent SSI, prevent SSI-related morbidity and mortality, reduce the duration and cost of health care (when the costs associated with the management of SSI are considered, the cost-effectiveness of prophylaxis becomes evident), produce no adverse effects, and have no adverse consequences for the microbial flora of the patient or the hospital.

To achieve these goals, an antimicrobial agent should be active against the pathogens most likely to contaminate the surgical site, given in an appropriate dosage and at a time that ensures adequate serum and tissue concentrations during the period of potential contamination, safely, and administered for the shortest effective period to minimize adverse effects, the development of resistance, and costs.

Surgical pathogens

To adjust antibiotic prophylaxis we need to know what the predominant organisms are:

In clean procedures, SSI is caused by skin flora, including S. aureus and coagulase-negative staphylococcus (e.g., Staphylococcus epidermidis)In clean-contaminated abdominal procedures and heart, kidney, and liver transplantations, the predominant organisms include gram-negative and enterococcus in addition to skin flora.

Drug administration

Timing: Delivery of the antimicrobial to the operative site before contamination occurs. It should be administered at such a time to provide serum and tissue concentrations exceeding the minimum inhibitory concentration (MIC).

    - First dose of antimicrobial beginning 60 minutes before surgical incision.     - Fluoroquinolones and Vancomycin require administration one to two hours before surgical incision.

Dosing: Antimicrobial-specific pharmacokinetic and pharmacodynamic properties and patient factors must be considered when selecting a dose.

Duration: The duration of antimicrobial prophylaxis should be less than 24 hours for most procedures  

Antibiotic prophylaxis in different procedures

Gastroduodenal procedures: Resection with or without vagotomy for gastric or duodenal ulcers, resection for gastric carcinoma, (PEG) insertion, perforated ulcer procedures (i.e., Graham patch repair), Whipple procedure and bariatric surgical procedures.

Organisms: E. coli, Proteus species, Klebsiella species, staphylococci, streptococci, enterococci and occasionally Bacteroides

Efficacy: Randomized controlled trials have shown that prophylactic antimicrobials are effective in decreasing postoperative infection rates in high-risk patients after gastroduodenal procedures.

Choice of agent: The most frequently used agents for gastroduodenal procedures were first and second generation cephalosporins.

Duration: The majority of studies evaluated a single dose of cephalosporin or penicillin

Recommendations for Gastroduodenal procedures

A single dose of cefazolin when the lumen of the intestinal tract is entered.In patients with b-lactam allergy: clindamycin or vancomycin plus gentamicin, aztreonam, or a fluoroquinolone

Higher doses of antimicrobials are uniformly recommended in morbidly obese patients undergoing bariatric procedures

Biliary tract procedures: cholecystectomy, exploration of the common bile duct and choledochoenterostomy.

Organisms: E. coli, Klebsiella species, and enterococci; less frequently,other gram-negative organisms,streptococci, and staphylococci are isolated

Choice of agent: The data do not indicate a significant difference among first, second, and third-generation cephalosporins.

Duration: A single dose of a cephalosporin was compared with multiple doses in several studies; no significant differences in efficacy were found

Recommendations for Biliary tract procedures

A single dose of cefazolin should be administered in patients undergoing open biliary tract procedures

Antimicrobial prophylaxis is not necessary in low-risk patients undergoing elective laparoscopic cholecystectomies

Antimicrobial prophylaxis is recommended in patients undergoing laparoscopic cholecystectomy who have an increased risk of infectious complications.

Because some of these risk factors cannot be determined before the surgical intervention, it can be reasonable to give a single dose of antimicrobial prophylaxis to all patients undergoing laparoscopic cholecystectomy.

Appendectomy

Organisms: anaerobic and aerobic gram-negative enteric organisms. Bacteroides fragilis is the most commonly cultured anaerobe, and E. coli is the most frequent aerobe.

Efficacy: Antibiotic prophylaxis is generally recognized as effective in the prevention of postoperative SSIs in patients undergoing appendectomy.

Choice of agent: An appropriate choice for SSI prophylaxis in uncomplicated appendicitis would be any single agent or combination of agents that provides adequate gram-negative and anaerobic coverage.

Duration: there was no discernible difference in postoperative SSI rates between single-dose and multidose administration in most studies.

Recommendations for Appendectomy

For uncomplicated appendicitis, the recommended regimen is a single dose of a cephalosporin with anaerobic activity (cefoxitin or cefotetan) or a single dose of a first-generation cephalosporin (cefazolin) plus metronidazole.

For B-lactam-allergic patients, alternative regimens include clindamycin plus (gentamicin, aztreonam, or a fluoroquinolone) and metronidazole plus gentamicin or a fluoroquinolone (ciprofloxacin or levofloxacin).

Small intestinal procedures: incision or resection of the small intestine, including enterectomy with or without intestinal anastomosis or enterostomy, intestinal bypass, and strictureoplasty

Organisms: Aerobic gram-negative enteric organisms. Other gram-negative bacilli of gastrointestinal enteric origin (aerobic and anaerobic) and gram-positive species, such as streptococci, staphylococci, and enterococci.

Choice of agent:

- No evidence of obstruction: a first-generation cephalosporin (cefazolin) is recommended.

- Patients with small intestine obstruction: a first-generation cephalosporin with metronidazole or a second-generation cephalosporin with anaerobic activity (cefoxitin or cefotetan) is the recommended agent.

Duration: additional intraoperative antimicrobial dosing dependent on the duration of the operation and no postoperative dosing, is recommended for patients undergoing small bowel surgery.

Recommendations for Small intestinal procedures

For small bowel surgery without obstruction, the recommended regimen is a first-generation cephalosporin (cefazolin)

For small bowel surgery with intestinal obstruction, the recommended regimen is a cephalosporin with anaerobic activity (cefoxitin or cefotetan) or the combination of a first-generation cephalosporin (cefazolin) plus metronidazole.

Hernia repair procedures: hernioplasty and herniorrhaphy

Organisms: The most common are aerobic gram-positive organisms. Aerobic streptococci, Staphylococcus species, and Enterococcus species are common, and MRSA is commonly found in prosthetic mesh infections.

Choice of agent: A first-generation cephalosporin is the recommended agent on the basis of cost and tolerability.

Recommendations for hernia repair procedures

For hernioplasty and herniorrhaphy, the recommended regimen is a single dose of a first-generation cephalosporin (cefazolin). For patients known to be colonized with MRSA, it is reasonable to add a single pre-operative dose of vancomycin to the recommended agent.

Colorectal procedures

-Organisms: B. fragilis and other obligate anaerobes are the organisms most frequently isolated from the bowel, with concentrations 1,000–10,000 times higher than those of aerobes. E. coli is the most common aerobe. B. fragilis and E. coli comprise approximately 20–30% of the fecal mass.

-Choice of agent: The combination of cefazolin and metronidazole provides adequate coverage of pathogens and can be a cost-effective prophylaxis strategy. Second-generation cephalosporins with anaerobic activity, such as cefoxitin and cefotetan, have been widely evaluated.

Combinations of oral and i.v. antimicrobials have been used in an attempt to further reduce postoperative infection rates. Regimens include oral neomycin and erythromycin plus i.v. administration of a cephalosporin, metronidazole and gentamicin plus clindamycin.

The evidence suggests that the combination of oral antimicrobials with MBP in addition to i.v. prophylactic antimicrobials reduces the rate of postoperative infections compared with i.v. antimicrobials alone without MBP, although the addition of oral antimicrobials increases gastrointestinal symptoms.

Recommendations for Colorectal procedures

A single dose of second-generation cephalosporin with both aerobic and anaerobic activities (cefoxitin or cefotetan) or cefazolin plus metronidazole is recommended for colon procedures.

In most patients, MBP combined with a combination of oral neomycin sulfate plus oral erythromycin base or oral neomycin sulfate plus oral metronidazole should be given in addition to i.v. prophylaxis

TAKE HOME MESSAGES

Surgical site infections (SSIs) are an important cause of healthcare-associated infection. They can be localized in the incision site or extend into adjacent deeper structures. Gastrointestinal procedures are among the highest risk procedures for SSI due to the presence of intraluminal bacteria.

Surgical antibiotic prophylaxis is an effective management strategy for reducing postoperative infections.

There are two key components of antimicrobial prophylaxis for prevention of SSI following gastrointestinal procedures: antibiotic selection and timing of administration. The choice of agents depends on the type of procedure.

SSIs are the most common and the costliest healthcare-associated infections and can be reduced by using antibiotic prophylaxis.