Antimicrobial Prophylaxis in Surgery

Antimicrobial Prophylaxis in Surgery

• Antimicrobial prophylaxis aims to reduce postoperative wound infections.
• Surgical site infections (SSIs) are infections related to incisions occurring within 30 days of surgery, or within 90 days if a prosthetic implant is involved.
• SSIs occur when a pathogenic organism multiplies in a surgical wound.
• SSIs can lead to local and sometimes systemic signs and symptoms.
• SSIs are associated with increased morbidity and extended duration of hospitalizations.
• Prophylactic antibiotics reduce SSI prevalence at the surgical site.
• Antibiotic prophylaxis involves pre-operative or intra-operative antibiotic administration to reduce post-operative infection risk.

Objectives

• The impact of surgical site infections (SSIs)
• Wound classification types
• Risk factors for postoperative surgical site infections
• Pathogens associated with different surgical operations
• Antimicrobial prophylaxis itself
• Importance of timing, duration, and re-dosing of antibiotics
• Recommendation of appropriate prophylactic antibiotics for a given surgical operation

Introduction

• Clinical use of antibiotics:
  • Prophylactic therapy: Given before contamination/infection.
  • Anticipatory therapy: Given when contamination has already occurred to minimize post-operative infections.
  • Empiric therapy: Non-directed therapy in the absence of pathogen identification.
  • Directed therapy: Therapy after pathogen identification.

Surgical Site Infection (SSI)

• Defined as infection related to incision
  • Occurs within 30 days of operative procedure or within 90 days if prosthetic material implanted.
• Pathogenic organism multiplies in a surgical wound, leading to local and sometimes systemic signs and symptoms.
• Increased morbidity and extended duration of hospitalizations are associated with SSIs.

By Definition

• SSI must occur within 30 days of surgery.
• If a prosthetic implant is involved, deep incisional or organ/space SSI can be reported up to 1 year from the surgery date.

Pathogenesis of SSI

• Endogenous:
  • Patient flora
  • Skin
  • GI tract
  • Mucous membranes (seeding from pre-existing infection sites)
• Exogenous:
  • Surgical personnel flora
  • Breaks in aseptic techniques
  • Inadequate hand hygiene
  • Equipment, surgical tools, materials within operative field
  • OR environment (ventilation)

SSI Pathogens

• Staphylococcus aureus (20-30%)
• Coagulase-negative staphylococci (13.7%)
• Enterococcus spp (11.2%)
• Escherichia coli (8-9.6%)
• Pseudomonas aeruginosa (5.6-8%)
• Enterobacter spp (4.2-7%)
• Klebsiella pneumoniae (3.0%)
• Candida spp (2.0%)
• Klebsiella oxytoca (0.7%)
• Acinetobacter baumannii (0.6%)

Risk Factors for SSI

• Patient characteristics:
  • Extremes of age
  • Obesity
  • Tobacco use
  • Malnutrition
  • Prolonged postoperative stay
  • Comorbid states
    • Diabetes
    • Remote infection
    • Ischemia
    • Colonization with microorganisms
    • Immunosuppressive therapy
• Operation characteristics:
  • Length of surgical scrub
  • Skin antisepsis
  • Preoperative shaving
  • Preoperative skin preparation
  • Length of operation
  • Inadequate instrument sterilization
  • Foreign material in surgical site
  • Surgical technique
  • Surgical wound class
  • ASA score
  • Unexpected contamination
  • Operating room ventilation

American Society of Anesthesiologists (ASA)

• Devised a preoperative risk score based on the presence of co-morbidities at the time of surgery.
• ASA score ≥ 2 is associated with increased risk of wound infection.

Wound Class

• Operations categorized into four classes:
  • Clean
  • Clean contaminated
  • Contaminated
  • Dirty
• Increasing incidence of bacterial contamination correlates to increasing postoperative infection rates.

Clean

• Uninfected operative wound with no inflammation.
• No entry into respiratory, alimentary, genital or urinary tracts.
• No break in aseptic technique.
• Wounds primarily closed following non-penetrating trauma.
• Infection Rate > 5%

Clean-Contaminated

• Operation with controlled opening of respiratory, alimentary, genital or urinary tracts.
• No evidence of infection, no major breaks in technique, no unusual contamination.
• Operation involving biliary tract, appendix, vagina, and/or oropharynx.
• Infection Rate > 10%

Contaminated

• Penetrating trauma or operation following open, fresh, accidental wounds.
• Operation with major breaks in sterile technique.
• Includes operations where acute, non-purulent inflammation is encountered.
• Infection Rate: 15-20%

Dirty

• Definition suggests organisms causing post-operative infection were present before the operation.
• Operation involving old traumatic wounds with retained devitalized tissue, or existing clinical infection, or perforated viscera.
• Obvious pre-existing infection present (abscess or necrotic tissue).
• Infection Rate: 30-40%

Recommendations for Surgical Prophylaxis

• Clean surgeries involving prosthetic material implantation.
• Clean-contaminated surgeries.
• Selected contaminated wounds.
• Dirty: Prophylaxis not indicated, antibiotics used for treatment.

Antibiotic Prophylaxis Goals

• Prevent infection & related morbidity/mortality.
• Reduce duration and healthcare costs.
• Minimize adverse effects on patient & hospital flora.
• Augment host defense mechanisms at the time of bacterial invasion (decrease inoculum size).
• Adjunct to good surgical technique, not a substitute.

Benefits & Risks

• Benefits: Decreased incidence of infection, lower costs, shorter hospital stays.
• Risks: Toxic reactions, allergic reactions, drug interactions, emergence of resistant bacteria, super-infection.

Principles of Surgical Antimicrobial Prophylaxis

• Principle 1: Use antibiotic when infection risk is high or sequelae is significant.
• Principle 2: Select the appropriate antibiotic effective against anticipated pathogens.
• Principle 3: Don't start too early or too late, administer when tissue levels will peak during the incision.
• Principle 4: Intravenous administration is preferred, effective dose based on patient weight.
• Principle 5: Additional intra-operative doses only necessary in long procedures or high blood loss cases.
• Principle 6: Keep post-operative doses minimal.

Prophylactic Antibiotics

• Most effective when administered within 1 hour before surgical incision.
• Should be administered ≤30 minutes pre-operatively for all surgical categories except cesarean section.
• Rates of infection increase significantly if antibiotics administered more than 1 hour before incision or postoperatively.
• Vancomycin and fluoroquinolones: administer first dose within 120 minutes of surgical incision (due to prolonged infusion times).

Summary

• Duration of surgical procedure and antibiotic half-life should be considered.
• Longer procedures may require additional intra-operative doses.
• Cefazolin 2 g (30 mg/kg in children and 3 g in adults ≥120 kg as single IV dose within 60 minutes prior to incision) is generally preferred regimen in surgical prophylaxis.
• Use Clindamycin or Vancomycin if patient has β-lactam allergy.

Summary of Specific cases

• Cardiothoracic: Cefazolin 2 g IV every 8 hours or Cefuroxime 1.5 g IV every 12 hours for a total of 48 hours.

Important Notes

• For patients with MRSA colonization, additional vancomycin dose is reasonable.
• Defined MRSA risk: History of MRSA colonization and infection or a high risk hospital patient for more than 5 days.
• Vancomycin administration: Give 1 g IV (1.5 g for patients >80 kg) 30-120 minutes before surgical incision and at 1g/hour (1.5g in 90 minutes).