Sterilization

Warm circulating air is used to remove ethylene oxide sterilant gas from packages in a special chamber.

Class 2 chemical indicator used in a prevacuum sterilizer to test the efficacy of the air removal cycle.

System of gathering and delivering instruments and supplies to the perioperative environment. Some models include provision for the return of instruments and contaminated items to the appropriate decontamination area after the surgical or interventional procedure.

Custom packs

Prepackaged collections of disposable supplies, drapes, sponges, and containers prepared by the manufacturer or the distributor according to specific instructions and requests by a particular service at a facility.

Flash sterilization

A rapid method of steam sterilizing properly prepared instruments for immediate use. These instruments are not wrapped. Flash sterilization is not the preferred method of sterilization.

Gravity displacement sterilizer

A steam sterilizer that uses steam in a downward motion to remove air from the sterilizing chamber. Air exits near front lower drain. Can be high speed or pulsing.

Indicator

Devices inserted into a packed set and attached to the outside of the wrapper/container used by health care personnel to monitor sterilization exposure conditions. Biologic indicators are the best indicators that parameters are adequate to kill microorganisms. Chemical indicators are not proof of sterility, but they signify that the item was exposed to the parameters necessary for sterilization. Autoclave tape is a class 1 type indicator.

Integrator

A chemical device inserted into a packed set that changes in response the time, temperature, and steam penetration to demonstrate visually that parameters necessary for sterilization have been met. An integrator mimics the conditions required of a biologic monitor.

Prevacuum sterilizer

A faster steam sterilizer that removes air by a vacuum before filling the chamber with steam. Also known as dynamic air removal steam sterilization.

Process challenge pack

A prepackaged unit consisting of dense materials and sterilization indicators or integrators used to test the effectiveness of the steam sterilizer.

Rigid container

An instrument case that seals and locks. Instruments are placed in a rigid container for sterilization.

Sterile

Microorganisms are at an irreducible minimum.

Sterilization

Processes by which all pathogenic and nonpathogenic microorganisms, including endospores, are killed. This term refers only to a process capable of destroying all forms of microbial life, including endospores. The sterilizer is a piece of equipment used to attain either physical or chemical sterilization. The agent used must be capable of killing all forms of microorganisms.

Strike through

Moisture or other substance penetrates through a sterile drape or wrapper to an unsterile surface.

Terminal cleaning

Thorough cleaning and disinfection of the perioperative environment at the end of use.

Terminal sterilization

Procedures carried out for the destruction of pathogens at the end of the surgical procedure in the OR or in other areas of patient contact (e.g., postanesthesia care unit [PACU], intensive care unit [ICU], patient care unit).

Turnover

Activity geared toward cleaning and preparation of the OR between cases for the next patient’s arrival.

Wet pack

Internal aspect of the sterile package remains moist or damp after passing through all sterilization parameters. Indicates a nonsterile item.

Wicking

Passage of fluids through a material by passive action. Also referred to as capillary action or strike-through.

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Sterilization versus disinfection

Pathogenic microorganisms, as well as those that do not normally invade healthy tissue, are capable of causing infection if introduced mechanically into the body. Standardized procedures that are based on accepted principles and practices are necessary for the sterilization or disinfection of all supplies and equipment used for patient care in the perioperative environment. Following established protocols for instrument processing helps minimize the patient’s risk for infection of the surgical site.

A sterile item has been exposed to a sterilization process to render it free of all living microorganisms, including endospores. As long as sterility is maintained, this process renders items safe for contact with nonintact tissue and for exposure to the vascular system without transmitting infection. The sterilization process should provide assurance that an item can be expected to be free of known viable pathogenic and nonpathogenic microorganisms, including endospores. For items and materials that cannot be sterilized, disinfectants are used to kill as many microorganisms in the environment as possible. (Decontamination and disinfection are described in Chapter 17.)

Sterilization

Bacterial endospores are the most resistant of all living organisms because of their capacity to withstand external destructive agents. Although the physical or chemical process by which all pathogenic and nonpathogenic microorganisms (including endospores) are destroyed is not absolute, supplies and equipment are considered sterile when all parameters have been met during a sterilization process.

Biologic indicators need to conform to the testing standards of the United States Pharmacopeia (USP). A control test is performed at least weekly in each sterilizer (Table 18-1). Many hospitals monitor on a daily basis; others test each cycle. Every load of implantable devices is monitored, and the implant should not be used until negative test results are known. All test results are filed in a permanent record for each sterilizer.

TABLE 18-1

Guidelines for the Use of Chemical and Biologic Indicators *

AAMI	AHA	AORN	CDC	TJC
CHEMICAL
Purpose: To indicate items exposed to the sterilization process; to monitor one or more sterilization parameters; to detect failures in packaging, loading, or sterilizer function. Indicators do not verify sterility.
Placement
External: On all packages except if internal indicator is visible	With each package; can be used inside or on outside	External: Visible on every package	External: Attached to each package	With each package, no designation to inside or outside
Internal: In center or area least accessible to sterilant within each package		Internal: Inside each package	Internal: Inside large pack
BIOLOGIC
Purpose: To document efficacy of sterilization process by killing resistant spores; to ensure that all process parameters are met; to detect nonsterilizing conditions in sterilizer.
Steam
Frequency: At least weekly, preferably daily	Frequency: Once a day	Frequency: At least once a week, preferable daily, and with each load of implants	Frequency: At least once a week, and with each load of implants	Frequency: At least weekly (daily is recommended), or with each load if sterilization activities are performed less frequently or if load contains implantable or intravascular material
Placement: Positioned in cold point in process challenge test pack, normally bottom front of sterilizer
Ethylene Oxide
Frequency: Every load	Frequency: Every load	Frequency: Every load	Frequency: At least once a week, and with each load of implants	Frequency: At least weekly (daily is recommended), or with each load if sterilization activities are performed less frequently or if load contains implantable or intravascular material
Placement: Inside pack in geometric center of load

^*All organizations require that indicators and integrators be used routinely.

Assembly of instrument sets

The weight of instruments and density of metal mass is distributed in the tray to allow steam penetration for sterilizing and revaporization for drying. A large tray distributes instruments so they make minimum contact with one another.

The size, design, and density of instruments are more important than their weight. The conditions necessary for steam sterilization are difficult to achieve in exceedingly heavy sets. Trays should not be overloaded. Closed container instrument sets should not weigh more than 25 pounds. Consideration is given to the personnel who must lift and move the packed sets when determining the presterilization weight. To assemble instrument sets for sterilization, the following steps should be performed:

1. Make sure the instruments are thoroughly dry. All instruments belonging to each set must have passed through terminal cleaning and terminal sterilization before they are safe to handle.

2. Unless contraindicated, place an absorbent towel or foam in the bottom of the tray to absorb condensate, as for a rigid container with vacuum valves. Include a biologic indicator or chemical integrator in the tray.

3. Count instruments as they are placed in the tray, and record the number of each type. A preprinted form is often used for this purpose. This form might be placed in the tray before wrapping and sterilization so the circulating nurse and scrub person can verify the baseline count. The form can be folded in half and placed in a paper peel pouch without a plastic coating to prevent printer toner from transferring to the instruments during processing. Concerns for toner particulate transfer to the instruments during the cycle are under study. The best choice may be to affix the tray inventory count sheet to the outside of the package.

4. Arrange the instruments in a definite pattern to protect them from damage and to facilitate their removal for counting and use. Follow the instrument book or other listing of instruments to be included.

5. Place heavy instruments, such as retractors, in the bottom of the tray.

6. Open the hinges and box locks on all hinged instruments.

7. Place ring-handled instruments on stringers or holders designed for this purpose. The curved jaws of hemostatic forceps and clamps should point in the same direction from smallest to largest. Instruments should be grouped by style and classification (e.g., six straight hemostats, six curved hemostats). Do not band with rubber bands. The metal under the band will not sterilize adequately.

8. Place sharp and delicate instruments on top of other instruments. They can be separated with an absorbent material or left in a sterilizing rack with the blades and tips suspended. The blades of scissors, other cutting edges, and delicate tips should not touch other instruments. If the instrument has a protective guard, leave it on. Tip-protecting covers or instrument-protecting plastic sleeves should be made of material that is steam-permeable and does not melt or deform with heat.

9. Place concave or cupped instruments with the cupped surfaces down so that water condensate does not collect in them during sterilization and drying.

10. Disassemble all detachable parts. Some parts, such as screws and springs, can be put in a peel pouch that is left open. Sealed pouches may not process correctly during the sterilization process.

11. Separate dissimilar metals. For example, brass knife handles and malleable retractors should be separated from stainless steel instruments. Preferably, put each metal in a separate tray, or separate metals with absorbent material.

12. Place instruments with a lumen, such as a suction tip, in as near a horizontal position as possible. These instruments should be tilted as little as possible to prevent trapped air or the pooling of water condensate.

13. Distribute weight as evenly as possible in the tray. Some trays have dividers, clips, and pins that attach to the bottom, which help prevent instruments from shifting and keep them in alignment.

14. Wrap the tray, or place it in a rigid container. Check woven textile wrappers for holes or abrasion. Sequentially double-wrap in a woven or nonwoven material, or use a double-thickness wrap in a single-fold configuration.

15. Place a chemical indicator tab or tape on the outside wrapper or container for proof that the package has been through the parameters necessary for sterilization.

16. Label the sets appropriately with their intended use (e.g., basic set), the date sterilized, and the process lot control number.

Packaging instruments and other items for sterilization

To be effective, the sterilizing agent must come into direct contact with all surfaces of every instrument. Therefore instruments must be packaged (individually or in sets) in such a way to allow adequate exposure to the sterilant, prevent air from being trapped and moisture from being retained during the sterilization process, and ensure sterile transfer to the sterile field.

The majority of surgical instruments are made of stainless steel and can be sterilized by steam under pressure. Effective steam sterilization involves the direct contact of all surfaces with steam and the revaporization of water condensate to produce a dry, sterile instrument.

Instrument packaging

For sterilizing and transporting, instruments are put in a closed container or wrapped individually. Instruments placed in open trays are wrapped as sets. Instruments may be sterilized unwrapped in a high-speed pressure sterilizer immediately before use, may be prepared in advance as for a case cart, or may be retained in sterile core storage until needed.

Packaging considerations

The packaging materials for all methods of sterilization should do the following:

• Permit penetration of the sterilizing agent to achieve sterilization of all items in the package.

• Allow the release of the sterilizing agent at the end of the exposure period and allow adequate drying or aerating.

• Withstand the physical conditions of the sterilizing process.

• Maintain integrity of the package at varying atmospheric and humidity levels. In dry climates or at high altitudes, some packaging materials are susceptible to rupture during sterilization or dry out and crack in storage.

• Provide an impermeable barrier to microorganisms, dust particles, and moisture after sterilization. Items must remain sterile from the time they are removed from the sterilizer until they are used.

• Cover items completely and easily and fasten securely with tape or a heat seal that cannot be resealed after opening. Seal integrity should be tamperproof. A margin of at least 1 inch (2.5 cm) is considered a standard for safety on all sealed packages.

Scissors should not be used to cut off the end of a package. Contents cannot be drawn out over this cut end because the contents would be contaminated by the edge of the packaging material. For the same reason, packages are never torn open below a seal.

• Resist tears and punctures in handling. If accidental tears and holes do occur, they must be visible.

• Identification label of the contents and chemical indicator evidence of exposure to a sterilizing agent should be visible on the outside of the package.

• Be free of toxic ingredients and nonfast dyes.

• Be lint-free or low-linting.

• Protect the contents from physical damage.

• Permit easy removal of the contents with transfer to the sterile field without contamination or delamination (separation into layers).

• Be economical.

Packages should be wrapped far enough away from sterile storage areas so that mixing sterile and nonsterile packages is not possible. Cabinets that contain nonsterile items should be labeled conspicuously. A procedure for sending items to and receiving items from the sterilizer should be set up so that sterile and nonsterile packages can never be confused en route. This procedure must be understood by everyone.

Packages may be wrapped with nonwoven or woven materials sequentially in two layers. Double-thickness wrapping in one layer without using the sequential method is also acceptable. The wrappers can be stitched around the edges or bonded/fused together. Aseptic presentation to the sterile field is the prime consideration. Each facility should determine which method and material is best suited to the clinical environment.

Items are enclosed with all corners of the wrapper folded in. Either a square or an envelope fold may be used (Figs. 18-1 and 18-2).

FIG. 18-1 Square fold for wrapping item for sterilization. Single-layer (double-thickness) heavy wrap may be applied in a nonsequential manner. *(Modified from the Association for the Advancement of Medical Instrumentation:* Good hospital practice: Steam sterilization and sterility assurance, *ANSI/AAMI ST46, Arlington, Virginia, 2009, American National Standards Institute.)*

• Sequential wrapping with two wrappers. An item is wrapped in one wrapper, the package is wrapped in a second wrapper. A cuff turned back on the first fold of each wrapper provides a margin of safety to prevent contamination when opening after sterilization. Packages can be fastened securely with chemical indicator tape.

• Single wrap. An item is wrapped in a single wrap that is of double thickness. The package is sealed with chemical indicator tape.

Packaging materials and methods

Packaging materials must be compatible with the sterilization process. The following materials may be safely used to wrap items for steam sterilization because they permit steam penetration, adequate air removal, and adequate drying.

Woven fabrics.

Reusable woven fabrics are commonly referred to as muslin or linen. When no other alternative is available, a 140-thread count, carded, 100% cotton muslin is used. Steam sterilizer cycles are based on a time-temperature profile of 140-thread count muslin. This type of fabric is not moisture resistant and is used in a double thickness. Two pieces are sewn together on the edges only, with a blind hem and without cross-stitching, so the wrapper is free of holes.

This wrapper should withstand between 50 and 75 launderings before becoming too worn to be a microbial barrier. A laundering mark-off system is helpful to monitor the number of times a wrapper has been used. The manufacturer should provide information about the number of launderings and sterilization cycles the wrapper can withstand.

Before resterilization, woven fabrics are laundered to rehydrate them. The moisture content of the woven material affects steam penetration and prevents superheating during the sterilization process. The fabric should be stored at a room temperature of 64° F to 72° F (18° C-22° C) and in a relative humidity of 35% to 70%. Before use, the woven fabric is inspected for holes and patched with vulcanized patches if necessary. Fabric may create free-floating lint in the OR.

Nonwoven fabrics.

Nonwoven fabrics are a combination of cellulose and rayon with strands of nylon randomly oriented through it, or they are a combination of other natural and synthetic fibers bonded by a method other than weaving. These fabrics have the flexibility and handling qualities of woven materials and are available in several weights. Lightweight is used in four thicknesses; medium weight is the most economical for wrapping items in two thicknesses; and heavy-duty weight is used when a single wrap is used for wrapping supplies for sterilization.

Packages are wrapped in the same manner as woven fabrics. Nonwoven fabrics provide an excellent barrier against microorganisms and moisture during storage after sterilization. They are disposable and virtually lint free. Some manufacturers provide a recycling service for nonwoven wrappers.

Peel packs or pouches.

Peel pouches and tubes made of a combination of paper on one side and clear plastic film on the other are satisfactory for wrapping single instruments, odd-shaped items, and small items. Double-sided paper pouches are commercially available. For sterile presentation, a peel-open seal may be preformed on one end. The open end is either heat sealed or closed with indicator tape after the item is inserted. All air is expressed from the package before sealing. Self-sealing pouches with adhesive flaps that do not require heat sealing also are available.

The sequential packaging of supplies in a smaller pouch into a larger pouch is not routinely necessary. However, this method may be useful for keeping multiple small items together, such as a set of bone screws. The aseptic presentation of tiny parts to the sterile field without dropping items on the floor can be accomplished with sequential packaging. The manufacturer’s instructions should be consulted if sequential peel pouches will be used.

A peel pouch should not be processed flat, but positioned on its side. The plastic side of the pouch can impede the flow of steam penetration through the package. Inclusion of plastic sided pouches within an instrument set can impair the process of steam through a tray. Obstruction of the steam flow can compromise the entire load. After processing, the peel pouch should be stored on its side to maintain integrity of the packaging.

Sealants and labeling.

Chemical indicator tape is used to seal packages such as peel pouches and wrapped items. Steam-sensitive tape resembles tan masking tape and reveals dark stripes when exposed to steam sterilizing conditions. Gas-sensitive tape is light green and reveals dark stripes after exposure to gas sterilizing conditions.

Peel pouches are usually heat-sealed or self-sealing and have an indicator area or dot that changes color in response to steam or gas exposure. They may be sealed with steam- or gas-sensitive tape. These sealants are not indicators of sterility but are a visual means by which to validate exposure to sterilant conditions.

The sealing tape on the outside of the package should be labeled with a dark marker that is resistant to moisture, bleed through, or smearing. Preprinted labels may be used instead. The date of processing and a load number should be attached to each package. These forms of identification are helpful in tracking and locating items that have been processed in batches. A recall of items may be necessary if the sterility of a particular load is in doubt.

Wrapped trays.

To allow steam penetration around instruments and prevent air from being trapped in the tray, trays cannot be solid. Therefore instruments are placed in open trays with mesh or perforated bottoms. Absorbent towels or foam may be placed in the bottom of the tray and over instruments to absorb condensate and protect instruments from snagging in the perforations. Trays are sequentially double wrapped in woven or nonwoven wrappers. They must be allowed to cool and dry at the end of the sterilizing cycle before they are handled. Condensation under the tray can generate strikethrough, promoting capillary action of moisture between the warm sterilized tray and the shelving. The moisture can carry microorganisms to the inside of the package.

Rigid closed containers.

A metal or plastic rigid closed container system may be used for sterilizing instruments singly or in sets. A stainless steel mesh or perforated basket lined with foam porous padding nests in the rigid container. The lid is affixed to the container base by metal snap locks. Plastic breakaway shrink bands secure the flip locks and act as chemical external indicators by changing color. The body of the container is labeled with the contents. A load-identifying label is affixed to the container before processing.

Most styles of closed containers have single-use unidirectional air filters in the lid and bottom. These filters are changed each time the container is processed. The closed container is placed into the steam sterilizer so the steam can penetrate through the bottom and lid. Some containers do not have vents in the bottom. The manufacturer of the closed container system should establish the processing temperature and time.

After the sterilization process is complete, the container is placed on a firm, dry surface adjacent to the sterile table. The circulating nurse breaks the shrink band seal by flipping open the locks and then lifts the lid toward himself or herself. The outer rigid container is not considered sterile. The scrub person carefully reaches into the container without touching it and grasps the handles of the sterile inner basket, lifting it straight up and out. The sterile basket containing the instruments can be placed on the sterile back table.

Sterile supplies are not to be opened into the rigid container, because the edges are not considered sterile. Condensate in the bottom of the nonvented closed container is considered sterile because it is not permeable to the capillary action associated with other packaging methods.

Specialized tray sets.

A manufacturer may supply a fitted case or rack for a set of instruments or implants, such as orthopedic devices. These cases or racks help protect the instruments and keep them separated for sterilization and use. These cases or racks are double wrapped before sterilization; they are not the same as rigid closed containers.

Count sheets.

Count sheets are sometimes packed inside the instrument set for use in counting instruments in the OR. The inks and toner pose a questionable risk for depositing foreign matter inside the patient during the surgical procedure. Toner in the printer cartridge is fused to the paper by heat. The transfer of the toner from the paper to the instruments is of concern during thermal sterilization. Although no data exist to demonstrate harm from toner on count sheets, no data are available to prove that toner is harmless.

Some facilities place the count sheet in a peel pouch. The plastic side of the pouch can obstruct the flow of steam if placed flat in the tray. Another option is to place the count sheet in a separate peel pouch and process separate from the packed tray.

Thermal sterilization

Heat is a dependable physical agent for the destruction of all forms of microbial life, including endospores. It may be used moist or dry. The most reliable and commonly used method of sterilization is steam under pressure.

Steam under pressure (moist heat sterilization)

Heat destroys microorganisms, and this process is hastened by the addition of moisture. Steam in itself is inadequate for sterilization. Pressure that is greater than atmospheric pressure is necessary to increase the temperature of steam for the thermal destruction of microbial life. Moist heat in the form of steam under pressure causes the denaturation and coagulation of protein or the enzyme-protein system within cells.

Direct saturated steam contact is the basis of the steam sterilization process. For a specified time and at a required temperature, the steam must penetrate every fiber and reach every surface of the items to be sterilized. When steam enters the sterilizer chamber under pressure, it condenses on contact with cold items. This condensation liberates heat, simultaneously heating and wetting all items in the load and thereby providing the two requisites: moisture and heat. This sterilization process is spoken of in terms of degrees of temperature and time of exposure—not in terms of pounds of pressure. Pressure increases the boiling temperature of water but in itself has no significant effect on microorganisms or steam penetration.

Exposure time depends on the size and contents of the load and the temperature within the sterilizer. At the end of the cycle, re-evaporation of water condensate must effectively dry contents of the load to maintain sterility; the water is dried from the sterilized pack or item.

The vegetative forms of most microorganisms are killed in a few minutes at temperatures ranging from 130° F to 150° F (54° C-65° C); however, certain bacterial endospores will withstand a temperature of 240° F (115° C) for more than 3 hours. No living thing can survive direct exposure to saturated steam at 250° F (121° C) for longer than 15 minutes. As the temperature of the steam is increased, the time of exposure may be decreased. A minimum temperature-time relationship is maintained throughout all portions of the load to accomplish effective sterilization.

Special circumstances

Prions (pronounced pree-ons) such as those that cause Creutzfeldt-Jakob disease (CJD) are not a living plant, animal, or virus.⁸ They are infectious protein material and the instruments used must be steam sterilized for a minimum of 1 hour at 270° F (132° C) after soaking in sodium hydroxide (bleach) or sodium hypochlorite at room temperature for 1 hour. This solution should be solidified and incinerated after use.

If a prevacuum sterilizer is used, the item can be safe to handle if processed for 18 minutes at 274° F (134° C) after the 1-hour exposure to sodium hydroxide. If a gravity displacement sterilizer is used the processing time increases to 1 hour. After the soaking and steam sterilizing procedures, the instruments can be processed through the routine washer-sterilizer procedure like other instruments.

Prion material becomes resistant to removal methods if left to dry. Instruments should be kept moist until they can be decontaminated and processed. Drapes and gowns should be incinerated because prions are not deactivated by laundry procedures. The use of disposable instruments and supplies is highly recommended.⁸

Eye instrumentation that is improperly cleaned and processed can subject the patient to toxic anterior segment syndrome (TASS). An inflammatory response in the anterior chamber of the eye causes permanent damage to intraocular tissues and predisposes the patient to secondary glaucoma.⁷ Eye instruments should be cleaned separately from other instruments.