Sterilisation in Anaesthesia

Definition

• Disinfection: destruction of pathogenic organisms but not all spores
• Antisepsis: disinfecting agents used on body surfaces (skin, mucosae)
• Asepsis: working systems designed to prevent organisms from reaching a protected environment (e.g., the operating room sterile field)

Spaulding Classification of Anaesthetic Equipment

Methods of Sterilisation Used in Anaesthesia

1. Autoclaving (Moist Heat / Steam under Pressure)

• Gold standard method
• Steam at 121°C for 15-20 min (at 15 psi) or 134°C for 3 min
• Kills ALL organisms including spores by protein denaturation
• Used for: metallic instruments, reusable laryngoscope blades, surgical tools
• Cannot be used for heat-sensitive plastics, rubber, or electronic equipment

2. Ethylene Oxide (EtO) Gas

• Cold sterilisation method - suitable for heat-sensitive equipment
• Alkylates nucleic acids and proteins, killing all organisms including spores
• Used for: plastic breathing circuits, ventilator tubing, LMAs, fiberoptic bronchoscopes
• Disadvantages: potentially explosive, carcinogenic, requires lengthy aeration (12-24 hours) before use to remove toxic residues, slow process (hours)

3. Glutaraldehyde (Cidex - 2% alkaline solution)

• High-level disinfectant / chemical sterilant
• Immersion for 10 hours achieves sterilisation; 20-30 minutes achieves high-level disinfection
• Used for: flexible endoscopes, fibreoptic laryngoscopes, anaesthetic equipment that cannot withstand heat
• Disadvantages: toxic/irritant to skin and mucous membranes, requires rinsing before use

4. Gamma Irradiation (Ionizing Radiation)

• Used industrially for single-use disposable equipment (syringes, needles, IV sets, ETT)
• Damages DNA, kills all organisms
• Cannot be used in clinical settings (requires industrial facility)

5. Dry Heat (Hot Air Oven)

• 160°C for 2 hours or 170°C for 1 hour
• Less efficient than autoclaving; used for glassware, oils, powders
• Rarely applicable in anaesthesia

Principles Relevant to Anaesthesia Practice

• Single-use disposable equipment (needles, syringes, ETTs, LMAs in many centres) eliminates cross-infection risk
• Prion disease (CJD): Standard autoclaving may NOT destroy prions. Dedicated or disposable equipment must be used for suspected cases. Incineration is the safest approach
• Bacterial spores (e.g., Clostridium) are the most resistant forms - only true sterilisation methods (autoclave, EtO, ionising radiation, prolonged glutaraldehyde) are sporicidal
• Mycobacteria (TB) are particularly resistant to many disinfectants due to their waxy cell wall - high-level disinfection with glutaraldehyde is required for equipment used on TB patients
• Viral contamination: HIV, HBV, HCV are relatively easily killed by most disinfectants; prions are the exception

Key Points Summary

1. Sterilisation = elimination of ALL organisms including spores (absolute term)
2. Method choice depends on the Spaulding classification of the equipment
3. Autoclave is the standard for heat-tolerant items; EtO for heat-sensitive items
4. Glutaraldehyde provides high-level disinfection/sterilisation for scopes
5. Prion safety requires special protocols beyond standard sterilisation