Instrument Sterilization
Part of Germ Theory
Methods for sterilizing or high-level disinfecting medical instruments before use in procedures involving tissue contact.
Why This Matters
Medical instruments that enter sterile body cavities or contact broken skin must be free of viable organisms, including spores. Before Lister introduced antiseptic surgery in the 1860s, surgeons operated with instruments cleaned only with rags — if at all — and mortality from post-operative infection approached 50%. The instruments themselves were delivering lethal doses of bacteria directly into wounds.
In a post-collapse medical context, you may need to suture wounds, perform minor surgery, deliver babies, extract teeth, or insert needles. Any instrument used for these purposes that is not properly sterilized will introduce organisms directly into tissue, bypassing all the body’s external defenses. A contaminated needle causes an abscess. A contaminated forceps in a surgical wound causes sepsis. A contaminated obstetric instrument causes the childbed fever that killed thousands of women annually before Semmelweis.
Understanding the hierarchy of sterilization methods and how to apply them with available materials is fundamental to providing safe medical care.
The Hierarchy: Sterilization vs. Disinfection
Sterilization: Complete elimination of all viable microorganisms, including spores. Required for instruments entering sterile body cavities or used in surgery.
High-level disinfection (HLD): Kills all vegetative bacteria, viruses, fungi, and most spores. Required for instruments contacting mucous membranes or broken skin. Acceptable for many medical procedures where true sterilization is not achievable.
Intermediate-level disinfection: Kills vegetative organisms but not all spores. Acceptable for surfaces and non-critical items.
Low-level disinfection: Reduces organism burden but is not reliable against all pathogens. For general surface cleaning.
In a field setting, aim for sterilization or HLD for all instruments that enter tissue. The method depends on available equipment.
Method 1: Pressure Steam Sterilization (Autoclave)
The gold standard. See the dedicated pressure sterilization article for full detail.
Requirements: Sealed pressure vessel, heat source, pressure gauge, safety relief valve. Parameters: 121°C at 15 psi gauge for 20 minutes (longer for wrapped or dense packs). Kills: Everything, including spores. Suitable for: Metal instruments, glass, cotton cloth and dressings, rubber (limited cycles). Not suitable for: Plastics that melt below 121°C, heat-sensitive materials.
Method 2: Dry Heat (Hot Air Oven)
Higher temperature required than steam sterilization (dry air is a poor heat conductor compared to steam).
Parameters: 160°C for 2 hours, or 170°C for 1 hour. Kills: Everything, including spores. Suitable for: Metal instruments and glass only (no rubber, no cloth, no plastics). Not suitable for: Anything that might char or melt.
Improvised hot air oven: A metal box or clay oven with a thermometer probe can function if temperature can be maintained consistently. A wood-fired clay kiln that can be controlled to 160-170°C and held there provides dry heat sterilization.
Calibrating temperature: At 160°C, sulfur (melting point 119°C) and tin (melting point 232°C) provide bracket references. A small piece of tin that remains solid confirms temperature is below 232°C; sulfur that has melted confirms above 119°C. Neither confirms exactly 160°C, but combined with timing, provides reasonable assurance.
Method 3: Boiling
The most accessible method. Detailed in the dedicated boiling article.
Parameters: Full rolling boil for 20 minutes. Kills: All vegetative organisms; does NOT reliably kill spores. Level achieved: High-level disinfection (not sterilization). Suitable for: Metal instruments, glass, cloth.
Practical guidance: For most procedures in the field — wound care, suturing, obstetrics, minor surgery — HLD by boiling is adequate. Truly sterile technique requiring spore elimination is most critical for deep surgical procedures, pressure sterilization is the standard.
The boiling protocol:
- Pre-clean instruments mechanically (scrub off all blood and tissue — boiling does not penetrate organic material)
- Submerge completely
- Bring to full rolling boil
- Time 20 minutes from onset of full boil
- Remove with boiled tongs
- Use immediately or store in a covered boiled container
Method 4: Chemical High-Level Disinfection
Chemical HLD is used when heat methods are not available or practical, or for heat-sensitive items.
Glutaraldehyde (2% solution): The most reliable chemical HLD and sterilant when used correctly. Commercial 2% glutaraldehyde (Cidex) is not producible from raw materials, but may be available from medical stockpiles.
- HLD: 20-minute immersion
- Sterilization: 10 hours immersion
- Rinse thoroughly with sterile water before use (glutaraldehyde is toxic to tissue)
High-concentration bleach (5000-10000 ppm available chlorine): Achieves HLD in 20 minutes for clean instruments. Use 10 mL of 5% bleach per 100 mL water (approximately 0.5% = 5000 ppm). Corrosive to metal — do not use routinely on metal instruments; suitable for glass and non-metal items. Rinse with boiled water before use.
70% Isopropanol or Ethanol: Rapid, effective against vegetative organisms and most viruses. Not effective against spores. Acceptable for instrument wiping between uses when boiling is not immediately available. Not a substitute for boiling before invasive procedures.
Protocol for chemical HLD:
- Clean instruments thoroughly — remove all organic matter (scrub under running water)
- Dry completely (many chemical disinfectants are inactivated or diluted by water)
- Immerse completely in the chemical agent for the required time
- Remove with sterile tongs (do not touch with ungloved hands)
- Rinse with sterile/boiled water (remove chemical residue that could damage tissue)
- Use immediately or store in a covered sterile container
Instrument Pre-Treatment: Cleaning
No sterilization method works on dirty instruments. Blood, pus, and tissue form a protective coating that harbors organisms and prevents heat or chemicals from reaching them. Pre-cleaning is as important as the sterilization step.
Immediate post-use treatment: Immediately after use, place instruments in a bucket of water to soak — prevents blood and tissue from drying and hardening. Dried blood is much harder to remove.
Mechanical cleaning: Scrub instruments with a brush (even a stiff-bristled natural brush) and soapy water. Pay attention to:
- Hinges and ratchets (forceps, needle holders)
- Serrations and teeth (tissue forceps, clamps)
- Inside of tubing (suction catheters, syringes)
- Needle hubs and tips
Rinse thoroughly with clean water to remove all soap. Soap residue inactivates some disinfectants.
For particularly contaminated instruments (used on known infections), pre-soak in 0.5% bleach for 10 minutes before mechanical cleaning, then clean normally.
Maintaining Sterility After Sterilization
Sterilized instruments must be kept sterile until use.
Wrapped sterilization: Instruments wrapped in cloth before autoclaving remain sterile inside the intact wrap for several weeks. The wrap acts as a bacteria-impermeable barrier when dry and undamaged. Handle wraps by the outside only; open immediately before the procedure.
Covered trays: Unwrapped instruments placed in a covered sterile metal tray can be maintained for a short period (hours). Avoid opening the cover until needed.
Storage environment: Cool, dry, low-dust. Humidity encourages organisms on surfaces; moisture wicks through wrapping material.
The 30-second rule: Any instrument placed in the sterile field and not immediately used should be considered contaminated if the sterile field was exposed to the environment for more than a brief period. When in doubt, re-sterilize.
Specific Instrument Considerations
Needles: Single-use in modern medicine. If reusing needles (a last resort), clean mechanically, then boil for 20 minutes. Inspect the needle tip under magnification — even a slightly bent or barbed tip will damage tissue and should be reshaped or discarded.
Surgical blades: Difficult to re-sterilize without dulling; more practically, sharp-edged stones can be used to fabricate stone blades, and new blades fabricated for each procedure.
Glass syringes: Boilable, reusable; disassemble before boiling to ensure the inside of the barrel is exposed to boiling water. Rubber plunger tips degrade with boiling — inspect each time.
Obstetric instruments: Forceps, scissors, and cord clamps used in delivery must achieve HLD minimum. Given the catastrophic consequences of puerperal infection (childbed fever), always boil obstetric instruments immediately before use, regardless of prior storage.