Sterilization Methods

This is Unit Six of Tech in Surgery Prep. Unit Five ended with a field where nobody had to guess what a container held. This unit asks the same of every instrument: how do we know it is sterile? Carry one idea through this lecture: the order of reasoning matters more than any single fact. Classify the item first, check what it is made of second, and let the manufacturer's tested instructions decide. The last worked example applies that order to three devices on one day. By the end you will be able to define sterilization and sort items by risk. To explain how steam sterilizes and where it can fail. To describe the low-temperature and other methods, with their limits. And to match a method to a device, package and load it correctly, and follow a tray through processing.

Four entries on what sterile means, how items are sorted by risk, and why cleaning always comes first.

The most extreme level of control.

TSC 126 Sterile Means No Living Microbes

Sterilization destroys or removes all forms of microbial life, including bacterial spores. It is the most extreme level of microbial control, reached by heat or by chemical sterilants. Anything less, including high-level disinfection, is not sterilization, and is not acceptable for an item entering sterile tissue.

Three classes of risk.

TSC 127 Critical, Semicritical, Noncritical

The Spaulding classification sorts items by infection risk, and the class decides the processing. If an item enters sterile tissue or the bloodstream, it is critical and must be sterile, like surgical instruments and implants. If it touches mucous membranes or broken skin, it is semicritical and needs at least high-level disinfection, like some endoscopes and anesthesia equipment. If it touches only intact skin, it is noncritical, and low-level disinfection is enough, like a blood pressure cuff. The scheme is a starting point: some complex devices do not fit it neatly, and then the manufacturer's instructions decide.

First, cleaning.

TSC 128 Cleaning Comes Before Sterilizing

Every item is cleaned with water and a detergent or enzymatic cleaner before it is disinfected or sterilized. Cleaning removes organic residue and salts that would shield microbes from the sterilizing agent. An item that has not been cleaned cannot be reliably sterilized, however good the sterilizer.

How many microbes are on it.

TSC 129 Why Bioburden Matters

Bioburden is the number of microorganisms on an item, and cleaning lowers it before sterilization. Microbes die at a steady logarithmic rate, so a heavier load takes longer to eliminate. Dried blood and tissue make cleaning harder, which is why soiled instruments are kept moist and cleaned as soon as possible.

Five entries on steam, the most widely used method, and on the ways it can fail to reach an item.

Four parameters, all required.

TSC 130 How Steam Sterilizes

Saturated steam under pressure is the most widely used and dependable method, killing by heating every surface it touches. Four parameters must all be met: dry saturated steam; pressure, which is how temperatures above boiling are reached; a sterilizing temperature, commonly one of two set points; and time, held long enough for the item, its wrapping and the sterilizer type. Moist heat destroys the proteins microbes need. It is the temperature, held for the right time with steam in contact, that kills spores, not the pressure. Exact cycle times come from the manufacturers' instructions, not memory.

Two ways to remove air.

TSC 131 Gravity and Prevacuum Cycles

The two basic steam sterilizers differ in air removal. In gravity displacement, steam pushes air out through a drain, which is slow in porous loads. In prevacuum, a pump removes the air first, so steam penetrates almost instantly. Trapped air blocks steam, which is why air removal is tested.

Only what the steam touches.

TSC 132 Steam Must Reach Every Surface

A sterilizer sterilizes only the surfaces its steam reaches. Hinged instruments are processed open, removable parts are taken apart, and concave items are placed so water drains. A closed hinge or a stacked basin can leave a surface the steam never touched.

Sterilizing for immediate use.

TSC 133 Immediate-Use Steam Sterilization

Immediate-use steam sterilization, long called flash sterilization, processes a cleaned item for use straight away, usually unwrapped or in a special rigid container. It is acceptable when an item cannot be packaged and stored first, or there is no time for the preferred wrapped method. It should not be used for convenience, to avoid buying sets, or to save time, and it is not recommended for implants; if unavoidable, records must link the load, the patient and the biological indicator. The item is used at once, and cooled first, because burns have been reported from hot instruments.

Moisture left inside.

TSC 134 Drying and Wet Packs

A wet pack still has moisture inside after the cycle ends. Heavy metal mass in a set is a known cause, along with dense wrap and set design. Moisture carries microbes from the air and surfaces, so a sterile item that becomes wet is considered contaminated.

Seven entries on the methods for items steam would damage, and on what each one demands.

A gas for sensitive devices.

TSC 135 Ethylene Oxide

Ethylene oxide is a gas that sterilizes items heat or moisture would damage, without harming their materials. Gas concentration, temperature, humidity and exposure time all affect whether it works. Its drawbacks are long cycles, cost, and hazards: it is flammable and explosive, the guideline says it should be considered a known human carcinogen, and workplace exposure is limited by federal rule. It is used for critical, and some semicritical, items that cannot be steamed. Residue left in a device can injure a patient, so aeration after the cycle is not optional.

Letting the gas leave.

TSC 136 Aeration After Ethylene Oxide

Items sterilized with ethylene oxide absorb some gas and must be aerated before use. Mechanical aeration takes many hours at raised temperature, room aeration takes days, and many modern sterilizers aerate in the chamber. An item released early carries toxic residue to patient and staff.

A low-temperature plasma.

TSC 137 Hydrogen Peroxide Gas Plasma

Hydrogen peroxide gas plasma is a low-temperature method that needs no aeration, because its by-products are water vapour and oxygen. The chamber is put under deep vacuum, hydrogen peroxide vapour spreads over the load, radio-frequency energy turns it into a plasma of reactive free radicals that kill microbes and spores, and filtered air restores normal pressure. It suits devices that cannot take heat or humidity. The load must be dry, or the vacuum fails and the cycle aborts, and linen and paper are not acceptable packaging.

A liquid for endoscopes.

TSC 138 Peracetic Acid Systems

Automated peracetic acid systems are a low-temperature liquid process, mainly for immersible items such as endoscopes. The sterilant is diluted, pumped through the device's channels and rinsed off, and items are used straight away, with no sterile storage. It must reach every channel, so the right connector for each device is essential.

Hot air, for a few materials.

TSC 139 Dry Heat

Dry heat sterilizes with hot air, for materials moist heat would damage or cannot penetrate, such as powders and oils. It penetrates them and does not corrode sharp instruments, but it is slow and needs high temperatures unsuitable for most materials, so it is a specialist method.

Sterile from the factory.

TSC 140 Radiation for Single-Use Items

Ionizing radiation, such as gamma rays, sterilizes many manufactured products but is not used in hospitals. Manufacturers use it for gloves, tubing and other plastics, which arrive already sterile in their packages. A commercially sterile item stays sterile only while its package is intact, which unit seven covers.

Liquid chemical sterilants.

TSC 141 Liquid Chemical Sterilants

Some liquid chemicals can sterilize heat-sensitive critical items when other methods are unsuitable. They work only if the item was cleaned first and the directions for concentration, contact time, temperature and acidity are followed exactly. A liquid process leaves no protective package, so the item is handled aseptically and used promptly.

Six entries on choosing the method, packaging and loading, then two worked examples. The opening idea is paid off at the last.

The order of the choice.

TSC 142 Matching Method to Material

The method is chosen by what a device is made of and what its manufacturer has validated. If it tolerates heat and moisture, steam is preferred, because it is dependable, fast, inexpensive and nontoxic. If not, a low-temperature method is chosen, each with its own limits on materials, packaging and lumens. If it is a powder or oil, dry heat may be used. In every case, the manufacturer's instructions name the tested methods, and they decide. An unvalidated method can leave a device unsterile or damage it, so a scrub person who sees an unfamiliar device asks how it was processed.

Long, narrow channels.

TSC 143 Long Lumens Are Hard to Sterilize

Every method must contact the microbes it kills, so long, narrow channels are hard to sterilize. The guideline reports that lumen length and diameter, salts and organic material can all reduce every method's effectiveness. So channels are cleaned thoroughly first and processed exactly as the manufacturer directs.

A package with four jobs.

TSC 144 Packaging for Sterilization

Packaging must let the sterilant in, then keep microbes out until the item is opened. Items are cleaned, dried and inspected, then placed in a tray with hinges open, parts apart, concave items draining and heavy items away from delicate ones. The set is enclosed in a rigid container, a peel pouch or wrap, and wrap goes on without tenting or gaps, often as two sheets. The packaging must suit the method. A good package lets the sterilant through, protects the item, keeps microbes out and keeps it sterile until use; a torn or wet package fails all four.

Arranging the load.

TSC 145 Loading the Sterilizer

A sterilizer load is arranged so the sterilant can circulate around every item. Perforated trays lie flat, parallel to the shelf; basins and other solid containers stand on edge; peel packs stand on edge in baskets. An overpacked chamber leaves cold spots where steam cannot reach.

One tray's journey.

TSC 146 A Tray's Journey Through Processing

A worked example, constructed for this course, follows a laparotomy tray. At the field, the scrub person wipes blood off, opens every hinge, removes sharps and keeps the instruments moist. In decontamination, staff in heavy gloves and eye protection take the set apart, clean it with enzymatic cleaner and a washer, and brush jaws and hinges by hand. In packaging, each instrument is inspected and the set assembled to its list, with a chemical indicator inside. It is double-wrapped, labelled with load information, and run in a prevacuum sterilizer that passed its air-removal test that morning. It cools and dries before handling, then goes to storage. Two days later, the scrub person checks the package and indicator before opening it. The scrub person starts the journey and finishes it.

Three devices, one order of reasoning.

TSC 147 Choosing a Method for Three Devices

A worked example, constructed for this course, pays off the opening idea. Stainless-steel retractors are critical and tolerate heat and moisture, so steam is used, as their instructions confirm. A camera head with electronics is critical too, but cannot take steam; its manufacturer lists hydrogen peroxide gas plasma, so the team uses that cycle, with the item dry and packaged in an accepted material. An instrument with a long, narrow channel gets the closest reading of its instructions, which specify thorough channel cleaning and a particular low-temperature cycle with the right connectors. Each time: classify, check the material, and let the tested instructions decide. When an instruction is missing, the device waits; it is not processed by guesswork.

Look at what you can now do. You can define sterilization, sort items as critical, semicritical or noncritical, and explain why cleaning and bioburden come first. You can explain steam's four parameters, the two ways air is removed, why every surface must be reached, when immediate use is acceptable, and why a wet pack is contaminated. You can describe ethylene oxide, gas plasma, peracetic acid, dry heat, radiation and liquid sterilants, with their limits. And you can match a method to a device in the right order, package and load it, and follow a tray through processing. Unit Seven asks how a team knows a package is still sterile when it is opened.