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ANTIBIOTIC STEWARDSHIP

MD Anaesthesiology Exam Notes

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1. DEFINITION & RATIONALE

• Anaesthesiologists are the primary administrators of perioperative antibiotic prophylaxis - the European Centre for Disease Prevention & Control places responsibility for appropriate timing directly on the anaesthesiologist
• ICU patients managed by anaesthesiologists are the highest consumers of broad-spectrum antibiotics
• Inappropriate use drives resistance, adverse effects, Clostridioides difficile infection, increased mortality, and cost
• Ambulatory antibiotic use accounts for ~85% of total antibiotic use; inpatient/ICU use contributes disproportionately to resistance burden

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2. CORE ELEMENTS OF ASP (CDC Framework)

Hospital-based ASP (CDC, 2019):

1. Leadership commitment - dedicated resources, written commitment
2. Accountability - single physician/pharmacist leader responsible
3. Drug expertise - pharmacist with ID/stewardship training
4. Action - at least one interventional policy (pre-authorization, prospective audit & feedback)
5. Tracking - monitor antibiotic prescribing and outcomes (resistance, C. diff rates)
6. Reporting - regular feedback to prescribers
7. Education - clinician and patient education

Outpatient/Ambulatory ASP (CDC, 2016):

1. Commit to improving antibiotic prescribing
2. Implement at least one policy/practice and assess effectiveness
3. Monitor prescribing and provide feedback
4. Provide educational resources to clinicians and patients

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3. PERIOPERATIVE ANTIBIOTIC PROPHYLAXIS (PAP) - Core Anaesthesia Responsibility

3a. Indications by Wound Classification

3b. Timing - The Decisive Window

• Prophylaxis must be given within 60 minutes before surgical incision
• Exception: Vancomycin and fluoroquinolones - give within 60-120 minutes (need infusion time to avoid reactions)
• Ideally at anaesthetic induction (Classen et al., NEJM 1992 - prospective study of 2,847 patients showed lowest SSI rate when antibiotics given 0-60 min before incision)
• Giving antibiotics >60 min before incision or after incision significantly increases SSI risk

3c. Intraoperative Redosing

• Procedure duration exceeds 2 half-lives of the antibiotic
• Significant blood loss (~half to one blood volume)
• Standard redosing intervals:

3d. Duration of PAP

• Single dose is preferred for most clean and clean-contaminated procedures
• No evidence for >24 hours - continuing prophylaxis beyond 24 hours does NOT reduce SSI and increases resistance risk
• Cardiac surgery: up to 48 hours acceptable (some guidelines)
• Stopping within 24 hours is standard; some data show single intraoperative dose is equivalent

3e. Agent Selection Principles

• Use the narrowest spectrum agent that covers likely pathogens
• Match agent to expected flora for each procedure type:

• Mild/moderate allergy: Cefazolin is safe (cross-reactivity <1%)
• Severe anaphylaxis to penicillin: Vancomycin or Clindamycin + Gentamicin

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4. SURGICAL SITE INFECTIONS (SSI)

Classification:

• Superficial incisional SSI: skin/subcutaneous tissue only
• Deep incisional SSI: fascial and muscle layers
• Organ/space SSI: any part of anatomy opened during surgery

Risk Factors (perioperative):

• Hyperglycemia (postoperative glucose >200 mg/dL significantly increases risk - target <180 mg/dL)
• Hypothermia (maintain normothermia throughout - oxygen delivery to wound is critical)
• Hypoxemia (oxygen and antibiotics have additive effects on reducing wound infection - Rabkin & Hunt)
• Obesity, immunosuppression, malnutrition
• Preoperative colonization with S. aureus/MRSA

Anaesthesiologist's role in SSI prevention (beyond antibiotics):

• Maintain normothermia (forced-air warming, warmed IV fluids)
• Optimise FiO2: supplemental oxygen (FiO2 0.80 vs 0.30) in colorectal surgery reduces SSI in some studies
• Glycaemic control: perioperative glucose management
• Preoperative skin preparation: antiseptic at induction
• Maintain tissue perfusion: avoid hypotension, ensure adequate cardiac output

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5. DE-ESCALATION STRATEGY

Steps:

1. Empirical broad-spectrum therapy - start promptly when infection suspected (don't delay)
2. Culture before antibiotics - blood cultures, respiratory samples, wound swabs
3. Reassess at 48-72 hours once culture/sensitivity results available
4. De-escalate to narrowest effective agent based on sensitivity profile
5. Determine duration - stop at the shortest effective course

Biomarkers guiding de-escalation:

• Procalcitonin (PCT): most evidence-based marker for antibiotic de-escalation and stopping decisions
  • PCT-guided therapy reduces antibiotic duration in HAP/VAP without worsening outcomes
  • PCT falling to <0.25 ng/mL or >80% decline from peak = consider stopping
• CRP: less specific; useful as trending marker
• WBC and clinical parameters: fever resolution, improving chest X-ray

Duration principles (HAP/VAP in ICU):

• 7 days is now recommended for most patients with HAP, including non-fermenting Gram-negatives (e.g., Pseudomonas)
• Short courses (7 days) equivalent to longer courses (8-15 days) for mortality, clinical cure, recurrence
• Barash Clinical Anesthesia, 9e: "De-escalation from empirical to targeted therapy should be performed by selecting antibiotics to which isolated bacteria are susceptible, then making the final choice based on PK/PD properties"

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6. PHARMACOKINETIC / PHARMACODYNAMIC (PK/PD) PRINCIPLES IN STEWARDSHIP

PK/PD Parameters:

Extended/continuous infusion of beta-lactams:

• Especially relevant in ICU: Piperacillin-tazobactam and meropenem can be given by extended infusion (4-hour infusion) to maximise T>MIC against resistant organisms
• Reduces antibiotic dose needed, reducing toxicity and costs

Antibiotic dosing adjustments in the ICU patient:

• Augmented renal clearance (ARC) - common in young septic patients; time-dependent antibiotics may have inadequate levels with standard dosing
• Renal impairment - prolonged levels; reduce frequency (not initial dose for aminoglycosides)
• Hepatic failure - affects metronidazole, clindamycin, tigecycline
• Obesity - use adjusted body weight for aminoglycosides; actual body weight for vancomycin loading

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7. CATHETER-RELATED BLOODSTREAM INFECTIONS (CRBSI)

Management (Barash, 9e):

• Early, appropriate broad-spectrum antibiotic coverage reduces mortality
• De-escalate promptly once organism identified
• Duration: typically 14 days for bacteraemia (longer for S. aureus, endocarditis, fungaemia)
• Line removal is the primary intervention - do not delay removal awaiting cultures

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8. VENTILATOR-ASSOCIATED PNEUMONIA (VAP) - ICU Stewardship

Key stewardship principles:

• Avoid unnecessary intubation and minimise ventilator days (SAT, SBT bundles)
• VAP prevention bundle: head-of-bed elevation 30-45°, oral chlorhexidine hygiene, cuff pressure monitoring, subglottic suction
• Diagnosis requires clinical + microbiological criteria - avoid treating colonisation
• Empirical therapy: cover MRSA (S. aureus) and Gram-negatives including Pseudomonas when risk factors present
• De-escalate based on culture results; 7-day course is adequate for most VAP
• Procalcitonin guidance can safely reduce antibiotic duration

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9. MECHANISMS OF RESISTANCE (Exam Mnemonics)

Resistance genes (Harriet Lane / clinically relevant):

• mecA - methicillin resistance (S. aureus → MRSA)
• vanA/B - vancomycin resistance (VRE)
• KPC - carbapenem resistance

• CTX-M - cefotaxime/3rd-generation cephalosporin resistance (ESBL)
• NDM (New Delhi metallo-beta-lactamase) - highly resistant, only polymyxins may work
• KPC - carbapenem resistance (Klebsiella pneumoniae)
• OXA, IMP, VIM - carbapenem resistance

Mnemonic for MDR Gram-negatives: "ESKAPE" organisms

• Enterococcus faecium
• Staphylococcus aureus (MRSA)
• Klebsiella pneumoniae
• Acinetobacter baumannii
• Pseudomonas aeruginosa
• Enterobacter species

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10. PROPHYLAXIS FOR INFECTIVE ENDOCARDITIS (IE)

Current AHA/ACC guidelines (relevant to anaesthesiologists):

• Prosthetic cardiac valves
• Previous IE
• Congenital heart disease (CHD): unrepaired cyanotic CHD, repaired CHD with residual defects, repaired CHD within 6 months of repair
• Cardiac transplantation recipients with cardiac valvulopathy

Procedures requiring prophylaxis in above patients:

• Dental procedures involving manipulation of gingival tissue, periapical region, or perforation of oral mucosa
• NOT required for respiratory, GI, or GU procedures (unless there is active infection)

Agent: Amoxicillin 2g PO 30-60 min before; Ampicillin 2g IV/IM if unable to take orally

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11. PROCALCITONIN (PCT) IN STEWARDSHIP

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12. MULTIDISCIPLINARY TEAM IN ASP

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13. INTERVENTIONAL STRATEGIES IN ASP

Prospective Audit and Feedback:

• Stewardship team reviews antibiotic prescriptions daily
• Provides direct recommendations to prescribing clinicians (face-to-face or via notes)
• Most evidence-based strategy - reduces C. difficile infection, resistance, and costs

Pre-authorisation (Restriction):

• Broad-spectrum agents require ID/pharmacy approval before dispensing
• Effective for controlling carbapenem and vancomycin use

Clinical Decision Support Systems (CDSS):

• Electronic alerts for dosing, duration, de-escalation
• Automated culture result review and alerts

Antibiotic Formulary:

• Restrict to evidence-based agents
• Remove redundant agents from formulary

De-escalation bundles and timeout:

• "Antibiotic timeout" at 48-72 hours: stop, reassess, de-escalate, define duration

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14. CONSEQUENCES OF POOR STEWARDSHIP

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15. QUICK REVISION TABLE FOR VIVA

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REFERENCES

• Barash, Cullen & Stoelting's Clinical Anesthesia, 9th edition - Chapter 8 (Perioperative Prophylaxis) & Chapter 20 (ICU Infections)
• Harrison's Principles of Internal Medicine, 22nd edition (2025) - Ambulatory Antibiotic Stewardship, p.296
• The Harriet Lane Handbook, 23rd edition - Antibiotic Therapy and Stewardship (Fig. 17.6, resistance gene summary)
• Murray & Nadel's Textbook of Respiratory Medicine - HAP/VAP De-escalation and Duration
• CDC Core Elements of Hospital Antibiotic Stewardship Programs (2019)
• Garnier M et al. Perioperative antimicrobial prophylaxis and SSI prevention Anaesth Crit Care Pain Med 2025 (PMID: 41022211)
• Barbato R et al. Antibiotic Prophylaxis in Cardiac Surgery ICU. Antibiotics (Basel) 2025 (PMID: 41009912)

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