Antimicrobial Prophylaxis - Shield Up, Scalpel Down!
- Goal: Prevent Surgical Site Infection (SSI); not to treat existing infection.
- Timing: Administer within 60 minutes before incision (📌 "One hour power hour"). For Vancomycin/Fluoroquinolones: 120 minutes.
- Selection: Based on common pathogens for the specific surgery & hospital antibiogram.
- Most common: 1st/2nd gen Cephalosporins (e.g., Cefazolin).
- Colorectal: Add anaerobic cover (e.g., Metronidazole).
- MRSA risk/beta-lactam allergy: Vancomycin or Clindamycin.
- Duration: Usually single dose; may extend up to 24 hours for certain procedures (e.g., cardiac, joint replacement).
- Redosing: For long surgeries (>2 half-lives of antibiotic) or major blood loss (>1500 mL).
⭐ Most SSIs are caused by patient's endogenous flora, primarily skin organisms like Staphylococcus aureus.
Wound Wisdom - Classify & Conquer
Surgical Site Infection (SSI) risk is stratified by wound classification. This guides antimicrobial prophylaxis decisions.
| Class | Description | SSI Risk | Prophylaxis |
|---|---|---|---|
| I: Clean | Elective, non-traumatic, closed; no inflammation. GI/GU/Resp tracts not entered. | <2% | No, unless high-risk (e.g., implant). |
| II: Clean-Contaminated | GI/GU/Resp tracts entered (controlled); no unusual contamination. Minor sterile break. | 2-10% | Yes, routine. |
| III: Contaminated | Gross GI spillage; fresh accidental wounds; major sterile break. Acute non-purulent inflammation. | 10-20% | Yes, often therapeutic. |
| IV: Dirty/Infected | Existing infection (pus); perforated viscera; old traumatic wound, devitalized tissue. | >20-40% | Yes, therapeutic. |
Antibiotic Arsenal - Pick Your Potion
- Goal: Bactericidal conc. at incision.
- Timing: IV <60 min pre-incision.
- Vanco/FQ: Infuse 60-120 min prior.
- Duration: Single dose; max 24h post-op.
- Redose: Long procedures (>2 T½); blood loss >1500mL.
- Cefazolin: q4h intra-op.
| Procedure Class | Agent(s) of Choice (IV) | Notes |
|---|---|---|
| Most Clean / Clean-Contaminated | Cefazolin 2g (3g if >120kg) | Skin, GI (upper), biliary, GU, Gynae. |
| Colorectal / Complicated Appendicitis | Cefazolin + Metro 500mg; OR Cefoxitin 2g | Anaerobic cover vital. |
| β-Lactam Allergy | Clinda 600-900mg; OR Vanco 15mg/kg | Vanco for MRSA. |
| Prosthetic Implants (Cardiac, Ortho, Vascular) | Cefazolin 2g (3g if >120kg) | Vanco if MRSA risk/allergy. |
Clocking Prophylaxis - Timing & Duration
- Initial Dose Timing:
- Standard agents (e.g., Cefazolin): IV within 60 minutes before incision.
- Vancomycin, Fluoroquinolones: IV within 120 minutes before incision (longer infusion).
- Aim: Adequate drug levels at incision.
- Intraoperative Redosing:
- If procedure > 2 drug half-lives.
- If blood loss > 1500 mL.
- Cefazolin: Redose q4h.
- Postoperative Duration:
- Usually single dose.
- Stop within 24 hours post-op.
- Avoids resistance; no added SSI benefit beyond 24h.
⭐ Administer most prophylactic antibiotics within 60 minutes before incision. Vancomycin and fluoroquinolones require infusion initiation 60-120 minutes before incision to ensure completion by incision time.
High‑Yield Points - ⚡ Biggest Takeaways
- Administer within 60 mins pre-incision (120 mins for vancomycin/fluoroquinolones).
- Aim for bactericidal drug levels in tissues at incision.
- Typically single dose; stop within 24 hours post-op.
- Cefazolin often used; choice based on surgery type & likely pathogens.
- Redose for long procedures (>2 drug half-lives) or major blood loss (>1500mL).
- Clean surgeries: Prophylaxis if high-risk (e.g., implant); not routine.
- Consider vancomycin for MRSA carriers or high local prevalence of MRSA.
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