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Sterilisation of Anaesthetic Equipment and Disinfection of the Operation Theatre

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1. Key Definitions

• Medical Microbiology 9e (Mandell), p. 28

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2. Spaulding Classification - Foundation for Anaesthetic Equipment

Only items used for invasive procedures require sterilisation; for most others, decontamination or disinfection may suffice. - PMC3821272

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3. Methods of Sterilisation

A. Autoclaving (Steam Under Pressure) - Gold Standard

• Mechanism: Moist heat denatures proteins
• Standard cycle: 121°C for 15 minutes (gravity displacement) or 132°C for 3-4 minutes (pre-vacuum)
• A drop of 1.7°C increases required exposure time by 48%
• Suitable for: Metal instruments, glass, linen, rubber ET tubes, reusable metal laryngoscope handles
• NOT suitable for: Heat/moisture-sensitive items (fiberoptic scopes, electronic equipment, plastic breathing circuits)

B. Ethylene Oxide (ETO) Gas

• Mechanism: Alkylates nucleic acids and proteins
• Conditions: 450-1200 mg/L at 29-65°C for 2-5 hours, followed by aeration for 12 hours to eliminate toxic gas
• Suitable for: Temperature- or pressure-sensitive items - fiberoptic laryngoscopes, flexible bronchoscopes, ventilator components, plastic circuits
• Limitations: Flammable, explosive, carcinogenic to animals - use only when alternatives are unavailable

C. Hydrogen Peroxide Plasma Gas (STERRAD)

• Mechanism: Oxidising free radicals destroy cell membranes and enzymes
• Conditions: 30% H₂O₂ at 55-60°C; the preferred modern replacement for ETO
• Cycle time: ~1 hour; no toxic residues remain
• Suitable for: Heat/moisture-sensitive instruments, metal items, electric and fiberoptic cables, rigid endoscopes
• NOT suitable for: Cellulosic materials (linen, cotton, paper), items that absorb H₂O₂
• Advantage: Does not require aeration; equipment can be used immediately

D. Glutaraldehyde 2% (Chemical Sterilant)

• 2% alkaline glutaraldehyde has better microbicidal properties than acid form
• Sterilisation requires 10-hour immersion; for HLD, 20-45 minutes suffices
• Equipment must be rinsed thoroughly in sterile solution after removal
• Safety concern: Respiratory irritant and sensitiser - use in ventilated areas

E. Peracetic Acid (0.2%)

• Excellent oxidising activity; end products (acetic acid + oxygen) are non-toxic
• Used in the Steris system for endoscope reprocessing

F. Dry Heat

• Requires 160°C for 2 hours or 170°C for 1 hour
• Damages most instruments; not currently recommended for anaesthetic equipment

G. Pasteurisation

• Hot water at 70°C for 30 minutes
• Used for breathing circuits, plastic corrugated tubing, humidifiers, nebulisers, face masks
• Less damaging than autoclaving; reliable, non-toxic, less expensive
• After pasteurising: dry equipment in a drying cabinet with HEPA filter

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4. Methods of Disinfection

Chemical Disinfectants Summary

• Medical Microbiology 9e, p. 28 (Table 3.2)

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5. Specific Anaesthetic Equipment - Practical Guide

Airway Equipment

Breathing Systems and Circuits

• Disposable breathing circuits: Single patient use; discard after each case
• Reusable circuits: Autoclaving or pasteurisation (70°C for 30 min)
• Bacterial/viral filters (HME filters) placed at the patient end of the circuit greatly reduce circuit contamination and extend reuse interval
• Soda lime canisters: Routine replacement; the canister itself can be autoclaved when empty

Anaesthesia Machine

• Internal components (rebreathing valves, CO₂ absorber housing): Dismantle and autoclave periodically
• External surfaces (control knobs, switches, trolley surface): Wipe with 70% isopropyl alcohol between cases
• Ventilator bellows and housing: Dismantle and autoclave or HLD
• Flowmeter knobs and monitor surfaces: Low-level disinfection with alcohol wipes

Invasive Monitoring Equipment

• Arterial line kits, CVP sets, PA catheters: Sterile, single-use
• Spinal/epidural needles and kits: Sterile, single-use (commercially gamma-irradiated)
• Transducer domes: Sterile, disposable

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6. Operation Theatre Disinfection

Zones of the OT Complex (Pye's Surgical Handicraft)

1. Outer zone (unrestricted) - corridors, changing rooms
2. Clean zone (semi-restricted) - scrub areas, equipment storage, anaesthetic room
3. Sterile zone (restricted) - the operating theatre itself
4. Disposal zone - dirty corridor for soiled materials and waste

• All personnel must change to OT clothing (cotton, freshly laundered) before entering
• Caps and disposable masks worn at all times (masks become permeable with time - change after long procedures)
• Antistatic boots or shoes restricted to OT use only
• OT is positively ventilated - all doors must remain closed to maintain the pressure differential
• One-way traffic: separate entry and exit doors minimise contamination risk
• Patients transferred to OT trolley/table before entering; ward beds/trolleys should not enter the OT

Ventilation

• Ultra-clean ventilation (laminar airflow) for orthopaedic and cardiac surgery: >300 air changes/hour
• Standard OT: 20-25 air changes per hour with HEPA-filtered air
• Positive pressure relative to corridors prevents ingress of contaminated air

Surface and Floor Disinfection

• Between cases: Wipe all surfaces (OT table, anaesthesia machine trolley, IV poles, overhead light handles) with freshly prepared hypochlorite (1000 ppm) or phenolic disinfectant
• End of day: Thorough mopping of floors with phenolic disinfectant; wipe all horizontal surfaces
• Fumigation (terminal/weekly): Formaldehyde gas (formalin 40%) or paraformaldehyde pellets. Procedure:
  • Close all doors/windows, seal gaps
  • Calculate volume (length × breadth × height)
  • Formalin: 500 mL/1000 cubic feet; heat to vaporise
  • Exposure time: minimum 24 hours
  • Potassium permanganate (KMnO₄) can be used to neutralise/oxidise formalin vapour after fumigation
  • Aerate thoroughly before allowing entry
• Modern alternative to formaldehyde: Hydrogen peroxide vapour (HPV) systems - more effective, less toxic, used in infection outbreaks

OT Table and Equipment

• OT table: Wipe with hypochlorite after each case; detailed disinfection at end of list
• Equipment packs returning from Central Sterile Supply Department (CSSD): Check for cleanliness, completeness, and sterility indicators (autoclave tape colour change, internal chemical indicator vials)
• Instrument trays: Autoclave tape changes colour; vial of fluid within the pack changes colour - both confirm sterilisation

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7. Infection Control Measures Specific to Anaesthesia Practice

Hand Hygiene

• Handwashing with soap and water: Standard pre/post patient contact
• Alcohol hand rub (70% isopropyl): Between procedures and before touching clean areas
• The WHO 5 Moments of Hand Hygiene apply to anaesthesia practice

Anaesthesia Work Area

• The anaesthesia work area (the anaesthetic cart and surrounding region) is a documented source of pathogen transmission
• Use single-use syringes and needles - never re-use
• Needle-stick protocol: Immediate first aid, report, test donor and recipient, post-exposure prophylaxis if indicated
• Label all syringes immediately after drawing up
• Separate clean and contaminated areas on the anaesthesia cart
• Use alcohol wipes to disinfect injection ports and vial tops before each access

Single-Use vs. Reusable Equipment

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8. Resistance Hierarchy of Microorganisms (Sterilisation Challenge)

1. Prions (most resistant - not inactivated by standard HLD; require 134°C for 18 min in porous-load autoclave, or 1M NaOH)
2. Bacterial spores (C. difficile, Bacillus)
3. Mycobacteria (M. tuberculosis)
4. Non-enveloped viruses (hepatitis A, poliovirus, norovirus)
5. Fungi
6. Vegetative bacteria, enveloped viruses (HIV, HBV, HCV)
7. Enveloped viruses (easiest to kill - killed by intermediate disinfectants)

Prions are not inactivated by high-level disinfection - Sleisenger & Fordtran's Gastroenterology

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9. Monitoring of Sterilisation Efficacy

• Packs should be checked for indicator colour change on receipt from CSSD before use in theatre - Pye's Surgical Handicraft, p. 121

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Summary Points for MD Anaesthesia Exam

1. Spaulding classification determines the level required (Critical=sterile, Semi-critical=HLD, Non-critical=LLD)
2. Autoclave (121°C/15 min) is the gold standard for heat-stable items
3. ETO for heat-sensitive items; must aerate 12 hours post-sterilisation
4. Plasma gas sterilisation is the modern ETO replacement; no toxic residue
5. 2% glutaraldehyde - HLD in 20-45 min, sterilisation in 10 hours; must be rinsed in sterile water
6. Pasteurisation (70°C/30 min) for breathing circuits and plastic equipment
7. OT fumigation with formalin (500 mL/1000 cu ft) for 24 hours; KMnO₄ used to neutralise
8. OT uses positive pressure ventilation with 20-25 air changes/hour (laminar flow for ortho/cardiac)
9. Bacterial/viral circuit filters (HME) at the patient port significantly reduce the need for circuit sterilisation
10. Prions require special high-temperature protocols; not destroyed by routine HLD