3.4 Equipment Sterilization & Maintenance

Decontamination and the Spaulding Classification

Sterilization is the process that destroys all microbial life, including bacterial spores. It is preceded by decontamination: gross debris is removed, instruments are cleaned (manual, ultrasonic, or washer-decontaminator), inspected, and lubricated. You cannot sterilize what is not first clean — bioburden and dried blood shield organisms from the sterilant.

The Spaulding classification (Earle Spaulding) determines the level of processing required based on infection risk:

All surgical instruments that enter the sterile field are critical items and therefore must be sterilized, not merely disinfected. Disinfection (using chemicals on inanimate surfaces) does not reliably kill spores, while an antiseptic is used on living tissue/skin — a distinction the CST exam tests. Sanitization merely reduces microbes to a safe public-health level and is the lowest tier.

Key definitions to keep straight:

• Sterilization — Destroys ALL microorganisms, including spores.
• High-level disinfection — Kills all organisms except large numbers of bacterial spores.
• Disinfectant — Used on inanimate objects (e.g., the OR table, instruments not entering the field).
• Antiseptic — Used on living tissue (the patient's skin prep, the surgeon's hand scrub).
• Bioburden — The number of microorganisms on a contaminated object before sterilization.

Proper decontamination workflow moves instruments from the dirty (decontamination) area to the clean (prep/pack) area in one direction only, preventing cross-contamination. Instruments are kept moist after use (covered with a wet towel or enzymatic spray) so blood and tissue do not dry and become impossible to remove.

Steam Sterilization (Autoclave) and IUSS

Steam under pressure (autoclave) is the preferred method: it is the most reliable, fastest, least expensive, and nontoxic. Sterilization depends on saturated steam contacting every surface at the right temperature, pressure, and time. The two standard temperatures are 250°F (121°C) and 270°F (132°C).

Gravity cycles let steam push air out passively; prevacuum cycles pump air out first for faster, deeper penetration of wrapped and lumened items. A drying time follows; wet packs are considered contaminated because moisture wicks bacteria through the wrapper.

Immediate-Use Steam Sterilization (IUSS) — the modern term for flash — sterilizes an unwrapped or specially containerized item that is needed urgently (e.g., a dropped instrument with no backup). Typical parameters are 3-4 minutes at 270-275°F (132-134°C). IUSS is for emergencies only; it is not acceptable for routine processing, for implants when avoidable, or as a substitute for adequate instrument inventory, because sterility cannot be maintained during transport of an unwrapped item.

Low-Temperature Methods

Heat- and moisture-sensitive items (flexible scopes, plastics, fiber-optics, some power equipment) require low-temperature sterilants.

• Ethylene oxide (EO/EtO) gas — Penetrates well and works at low temperatures, but is toxic, flammable, and carcinogenic and requires a long aeration period to off-gas before items are safe to use; total turnaround can be 10-16+ hours. Items must be completely dry (EO + water forms toxic ethylene glycol).
• Hydrogen peroxide gas plasma (e.g., Sterrad) — Vaporized hydrogen peroxide is energized into a plasma; fast (often under an hour), low-temperature, and leaves only water and oxygen, but cannot process cellulose (paper, cotton/linen) or long narrow lumens without boosters.
• Peracetic acid — A liquid chemical sterilant (e.g., STERIS system) for immersible items like endoscopes; uses ~0.2% solution and produces just-in-time sterile, non-wrapped items for immediate use.
• Ozone and chlorine dioxide are additional options.

Sterility Monitoring

Every load and the equipment itself must be verified:

A BI is run at least daily and with every implant load; a positive BI means the load is recalled. Chemical indicators alone never prove sterility — only that conditions for sterilization may have been present.

Packaging, Loading, and Shelf Life

How items are wrapped and loaded determines whether the sterilant can reach every surface:

• Packaging must be compatible with the method (e.g., paper/cotton is fine for steam and EO but cannot be used in hydrogen peroxide gas plasma, which the cellulose absorbs).
• Hinged instruments are sterilized open/unlocked so steam contacts the box lock.
• Items are loaded so packs do not touch the chamber walls and steam circulates freely; heavy sets go on lower shelves.
• After the cycle, packs must be completely dry; a wet pack is contaminated.

Event-related sterility is the modern standard: a wrapped, properly stored sterile item is presumed sterile until a specific event (tear, moisture, dropped pack, broken seal) compromises it, rather than a printed expiration date. Before opening any package onto the field, the CST inspects the wrapper integrity, checks the external chemical indicator for the correct color change, and confirms the package is dry and intact.