8.1 Sterilization Methods and Validation

For the Certified Surgical First Assistant (CSFA), a comprehensive understanding of sterilization methods is vital to maintaining the sterile field and preventing surgical site infections (SSIs). Sterilization is the absolute destruction of all microbial life, including highly resistant bacterial spores, viruses, and fungi. This section details the principles, methods, and validation protocols for surgical sterilization.

The Spaulding Classification System

Before selecting a sterilization or disinfection method, devices are categorized according to the Spaulding Classification System, based on their intended patient contact:

1. Critical Items: Instruments or devices that enter sterile tissue or the vascular system (e.g., surgical instruments, implants, needles). Requirement: Must be sterile.
2. Semi-critical Items: Devices that come into contact with intact mucous membranes or non-intact skin (e.g., endoscopes, anesthesia equipment). Requirement: High-level disinfection (HLD) minimum, though sterilization is preferred if the item can tolerate it.
3. Non-critical Items: Items that touch only intact skin (e.g., blood pressure cuffs, bedpans). Requirement: Intermediate- or low-level disinfection.

Steam Sterilization (Autoclaving)

Steam sterilization under pressure is the most economical, safe, and dependable method for items that can withstand high heat and moisture. It kills microbes by denaturing and coagulating their cellular proteins. The critical parameters for steam sterilization are time, temperature, pressure, and moisture.

Types of Steam Sterilizers

1. Gravity Displacement Sterilizer: Steam enters the top of the chamber and actively displaces the heavier air, forcing it out through a drain at the bottom.

• Standard Parameters (Wrapped Items): 250°F (121°C) at 15-17 psi for 30 minutes.
• Standard Parameters (Unwrapped, no lumens): 270°F (132°C) at 27-30 psi for 3 minutes.

2. Prevacuum (Dynamic-Air-Removal) Sterilizer: A vacuum pump forcefully extracts air from the chamber before steam is introduced, allowing for near-instantaneous steam penetration, even into dense packs and lumens.

• Standard Parameters (Wrapped Items): 270°F (132°C) at 27-30 psi for 4 minutes.
• Bowie-Dick Test: Must be performed daily (usually the first run) on prevacuum sterilizers to verify the vacuum system is functioning correctly and removing air. It is a chemical indicator, not a biological one.

Immediate-Use Steam Sterilization (IUSS)

Formerly known as "flash" sterilization, IUSS is strictly reserved for emergencies (e.g., a one-of-a-kind instrument is dropped). It must never be used for convenience or to compensate for inadequate instrument inventory. Implants should generally never undergo IUSS; if an absolute emergency dictates it, a rapid-readout biological indicator must be run with the load.

Low-Temperature Sterilization Methods

Certain delicate instruments (plastics, cameras, fiber-optic light cords, delicate power tools) cannot withstand the heat and moisture of steam. These require low-temperature methods.

Ethylene Oxide (EtO) Gas

EtO is a highly toxic, flammable gas that kills microorganisms by interfering with their normal metabolism and protein synthesis (alkylation).

• Advantages: Excellent penetration; safe for almost all heat- and moisture-sensitive items.
• Disadvantages: Very long cycle times (up to 12 hours) and requires mandatory, lengthy aeration (8-12 hours at elevated temperatures) to remove toxic gas residues. EtO exposure is highly dangerous to personnel.
• Parameters: Time, temperature, humidity (usually 40-80%), and gas concentration.

Hydrogen Peroxide Gas Plasma

Often referred to by the brand name Sterrad, this method uses a low-temperature plasma field generated from hydrogen peroxide vapor to destroy microbes via oxidative damage.

• Advantages: Fast cycle times (28-75 minutes); no toxic residue (byproducts are simply water vapor and oxygen); no aeration required.
• Disadvantages: Cannot penetrate long, narrow lumens effectively unless specially adapted; strictly incompatible with any cellulose-based materials (paper, cotton, linen wrappers) because cellulose absorbs the hydrogen peroxide, causing the cycle to abort.

Liquid Chemical Sterilants

Chemicals like glutaraldehyde (Cidex) and peracetic acid (Steris System 1E) can serve as high-level disinfectants or sterilants depending on the exposure time.

• Glutaraldehyde: Requires 20-45 minutes for high-level disinfection, but a full 10 hours of complete immersion to achieve sterilization (sporicidal action). Items must be thoroughly rinsed with sterile water afterward.
• Peracetic Acid: Typically used in automated processors for immediate use of immersible, heat-sensitive endoscopes. Cycle takes about 20-30 minutes at 122-131°F (50-55°C).

Validation of Sterilization

Ensuring the effectiveness of a sterilization cycle requires mechanical, chemical, and biological monitoring.

1. Mechanical/Physical Indicators

These are the gauges, dials, and printouts on the sterilizer machine itself. They verify that the required parameters (temperature, pressure, time) were met during the cycle. They do not prove sterility, only that the machine functioned as programmed.

2. Chemical Indicators (CIs)

Chemical indicators use sensitive chemicals that change color when exposed to specific sterilization parameters.

• External CIs: (e.g., autoclave tape) Placed on the outside of packages. They only indicate that the package was exposed to the sterilant (like heat), distinguishing processed from unprocessed items.
• Internal CIs: Placed inside every package, in the area most difficult for the sterilant to reach.
• Class 5 Integrating CIs: The most sophisticated chemical indicators; they react to all critical parameters (time, temperature, and moisture/sterilant presence) and match the performance of a biological indicator.

3. Biological Indicators (BIs)

BIs are the gold standard and the only definitive test that guarantees sterilization has occurred. They contain highly resistant bacterial spores in a vial. After the cycle, the vial is incubated. If no growth occurs, the cycle was successful.

• Geobacillus stearothermophilus: Used for testing steam and hydrogen peroxide gas plasma sterilizers. Incubated at 131-140°F (55-60°C).
• Bacillus atrophaeus: Used for testing Ethylene Oxide (EtO) and dry heat sterilizers. Incubated at 95-98.6°F (35-37°C).

According to recommended practices, a BI should be run at least weekly (preferably daily), and always with any load containing an implantable device. The implant should not be released until the BI results are negative.