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How to Prevent Infection from Surgical Instruments
Follow the rules and you won't go wrong.
Dan Mayworm
Publish Date: October 10, 2007   |  Tags:   Infection Prevention

Instrument sterilization may be the most well researched and well controlled portion of surgical infection control. When the rules of proper decontamination, packaging and sterilization are followed, the incidence of surgical site infection from reusable surgical instruments and supplies is extremely low. The challenge, especially today with so much decentralization of surgery, is making sure that everyone involved in the sterilization process is well-versed in its principles. This overview, which is broken down into four sections, is designed to help.

 Within this document:

How to Decontaminate Instruments
Decontamination of surgical instruments may actually be the most important step in the instrument care process, because no sterilization system can reliably penetrate caked on biological material. Here's advice on how to do it properly:

First, thoroughly pre-clean the instruments. Left alone, blood and other debris can rapidly dry and coagulate on the surfaces of surgical instruments, making effective cleaning nearly impossible. So start decontamination immediately after the surgeon is finished with the device, particularly if the device is complex.

As soon as the surgeon is finished with a submersible device, place it in a basin or tray containing an enzyme solution. Disassemble complex devices (including scissors) and open any hinged instruments before placing them into the solution. Special trays may be necessary for delicate instruments. Be aware that some lumened instruments require flushing.

If an enzyme solution is inappropriate for the instruments in question, remove gross debris by holding the instruments under a faucet and then place them in a covered tray filled with tap water.

Transport the instruments to the decontamination area (which should be a separate, well-lit room with its own negative-pressure air circulation system, washable walls and ceilings, a sink and a floor drain) in a closed cart or sealed container.

In a small facility, it's possible to decontaminate instruments by hand. For this, you need only a sink and an assortment of cleaning brushes and tools. If you're in a large, busy facility, however, you may want to automate the process. Several devices may help you do this. A rundown of what's available:

Cart washers will handle your case carts, transport carts, and other mobile equipment in much the same way as a car wash handles your car. Insert the cart in one end, start the washer, and wait for it to come out clean on the other end. If you don't have a cart washer, you may want to equip your room with a power washer and drain. Please note that some portable equipment cannot withstand either a cart washer or a power washer; if this is the case, you'll need to wipe down the equipment by hand.

Single-chamber washers operate in basically the same way as your home dishwasher. You will need to separate the items and place them in special baskets that allow the high-pressure water to reach all surfaces. Some washers include attachments for special items such as endoscopes. Single-chamber washers differ in their degree of automation. Some simply wash and rinse. Others are fully automatic, featuring everything from power doors to operator- selected cycles, to automatic loading and unloading.

Tunnel washer/sterilizers may be appropriate for very high-volume facilities. These devices index and automate the various steps of pre-rinsing in cold water, detergent hot-water washing, ultrasonic cleaning, instrument lubrication, sterilization, and drying. It's questionable if the sterilization cycle is necessary. Some users believe that if the washer/sterilizer doesn't clean exceptionally well, the sterilization process will bake on whatever the cleaning cycle misses. However, if you are more comfortable having your instruments decontaminated and sterilized before you run them through the standard packaging and sterilization process, they may be worth the cost.

Ultrasonic cleaners may be useful for instruments with difficult-to-clean surfaces, like serrated tips and box locks.

After thorough rinsing, you may wish to dip instruments in a water-soluble lubricant (often called "instrument milk" because of its milky color and consistency) to lubricate instruments with hinges or moving parts and provide surface protection. Always follow the manufacturer's instructions for use. Do not use mineral oil or other oil-based lubricants.

How to Package Instruments Effectively
Health care facilities take great care to achieve sterilization, but they sometimes fail to take the same care to ensure that the products are sterile at the time of use, which is, of course, the only time that matters. To keep a product or device sterile, it's crucial to protect and store it with appropriate packaging. There is much to know about this subject. Here's an overview.

Types of Packaging
Essentially there are three:

  • CSR Wrap. These materials come in reusable and disposable varieties. I generally recommend disposable; the old muslin wraps are not safe and the newer, more tightly woven reusable wraps, while safe, are a lot of trouble to care for to ensure effectiveness.

    Disposable non-woven wraps are not without problems. They do not drape as well as the reusable wrap, potentially hindering aseptic technique during the presentation stage. They do not absorb moisture thereby potentially causing wet packs in heavy trays. They sometimes conform poorly to the instrument, causing too small wraps to blow out during the vacuum cycle and large wraps to wrinkle, They also tear easily. Using towels inside the packages to cushion sharp corners (and absorb excess moisture), avoiding the stacking of trays and carefully handling the packages will all help prevent tearing.

  • Paper/Plastic Pouches. Designed initially to contain single instruments, paper/plastic peel pouches are now used to package everything from sterile gauze packs to uncomplicated instrument sets. These feature a special grade of paper on one side and a lamination of polypropylene and polyester on the other. They come in many sizes, both as preformed pouches and rolls of tubing.

Pouches offer a number of advantages — they're easier to work with than double CSR wraps, allow you to see the contents, are relatively inexpensive, seal quickly and easily and afford simple aseptic presentation. A potential disadvantage is that the paper side is subject to moisture contamination and easy to compromise.

A New Way to Wrap "In the Box"

If you use non-woven disposable wraps to wrap your instrument trays, you may have run across this problem. Tightly wrapped trays, especially the older ones with sharp corners, tend to puncture the wraps during the sterilization process and subsequent handling. Non-woven wraps, because of their physical structure, tear more easily than the woven variety.

Here's an easy, cost-effective way to solve this problem. Instead of wrapping the entire tray, wrap only the instruments inside using the method depicted here. This way, the instrument tray itself serves as the sterilization container system, complete with handles to make the package easy to transport. The contents of the tray are kept up and away from any casual surface moisture that would contaminate the contents. Most importantly, you can use the least expensive type of wrap and not worry about the wrap tearing.

To make sure you don't compromise sterility in the OR, place the tray on a back table or a separate table close to the sterile field, much as you would a sealed container sterilization system. Or, you can place the tray at one end of the sterile field, and when you unwrap the instruments, carefully drape the wrap over the outside edge of the tray, creating a new sterile field around its perimeter.

Some recommendations regarding pouches:

  • When possible, use pre-formed pouches rather than tubing; they are cheaper when you consider the labor. Use tubing only for long, narrow devices like catheters for which there is no preformed pouch available.
  • Use flat pouches, not gussetted ones. Contrary to popular belief, flat pouches hold more. They allow more steam and air to penetrate. And they are easier to seal.
  • Choose heat sealing if possible. It is cheaper and more efficient than using self-sealing pouches. Use self-seal pouches only when it is impractical to have a dedicated heat sealer in the area where the packaging is being done. An inexpensive, wide, flat or serrated hot bar sealer is all you need.
  • In general, use single- rather than double-pouching.
  • Buy pouches with tack seals above the chevron so that this area does not collect dust.
  • Buy pouches with minimal printing on them and printed chemical indicators only above the chevron seal. Printed internal indicators are of dubious value.
  • Rigid container systems. These are aluminum, stainless or plastic valved boxes, often specially designed for certain instrument sets. They offer several advantages over the previous two options; they are more protective, more environmentally friendly, and more convenient in some ways. But if you don't keep them in use they take up a lot of storage space, they are not cheap, their filters and valves can provide an entry for contamination, they require routine preventive maintenance, and importantly, not all container systems work with all sterilizers or all instruments. Test any container with your sterilizer and instruments prior to buying.

How to arrange your packages
Arranging instruments properly for steam sterilization can be a significant challenge. Here are some tips on how.

For textile packs, the most important factor when assemb-ling an instrument set is to make sure that the steam can contact every part of each instrument.

Weight for different-sized baskets

10 x 20 basket 


15.0 lbs. 

90 instruments 

10 x 15 basket 


11.0 lbs. 

66 instruments 

10 x 10 basket 


7.5 lbs. 

45 instruments 

10 x 30 basket 


19.0 lbs. 

114 instruments 

Set up the pack so that if you were to look at a cross-section of it, you could envision an unimpeded flow of steam from the top to the bottom.

Make sure the outer wrap is just tight enough to hold the contents together and not so tight that steam will have a difficult time penetrating and cause pooling. Also, don't load packs on the cart too tightly. You should be able to easily pass your hand between the packs.

Do not put too many items in the pack. Too much metal mass in too confined a space is a common cause of wet packs. The maximum weight and number of instruments in a set based upon a baseline of 90 instruments weighing 2.6 oz. each per 10" x 20" basket weighing a total of 15 lbs is shown in the chart at left.

When instruments weigh less, you can include a greater number per pound. If they weigh more, you'll be able to safely sterilize fewer instruments in each basket, even though more may fit.

Other tips for assembling instrument sets:

  • Use a mesh or wire-bottom tray so water can't pool in the bottom of the tray. Avoid using "cake-pan" flat trays unless you are sterilizing just a few small instruments.
  • Always use a tray large enough to distribute the metal mass evenly within the tray.
  • Load the instrument sets flat on the sterilizer cart. Do not place them on edge; the instruments inside will fall to the bottom and create a heat-sink mass of metal and more condensate than can be evaporated.
  • When assembling basin sets, position items so that all water can drain out. Separate nested items with absorbent towels. Don't include anything in the set that could shift out of position and trap moisture.
  • Develop and adhere to a communications system that will alert the person loading the sterilizer where the standing edge is. For example, you can seal the set so that the tape is on the edge that should be placed down. Or, draw an arrow on the tape indicating which way to place the set.
  • To prevent tears in the textiles, consider wrapping the instruments inside the tray rather than the tray itself.

When positioning pouches, always place them on edge and pack them loosely in the basket. Leave room for steam penetration and moisture removal.

  • Never include peel pouches inside instrument sets.

When using containers, check the container prior to loading it. Make sure all mating surfaces are clean and free of dents and chips. Gaskets should be free of any breaks or cuts, pliable, and properly seated. Also check valves and filters for proper function and integrity.

The weight and distribution of instruments in containers is even more critical than with wraps because aluminum and stainless steel containers add metal mass and weight. If the quality of your steam is suboptimal, you may have to use absorbent materials within the container or the basket to absorb excess moisture.

Use dividers, stringers, and sorting pins to contain and separate items.

Open jointed instruments and disassemble complex ones unless testing in your systems proves this unnecessary.

Load lumened items with moisture in the lumens. The moisture will turn to steam and push out the air.

Place items with surfaces that will pool water on edge and secure them so that they don't fall over during sterilization.

Always place containers flat on the cart. This makes it easier to predict the action of the steam on the instruments inside the container.

Place internal chemical indicators in a corner at the bottom of the container or anywhere else it is difficult for the sterilant to reach. Don't just toss the indicator in the basket.

Avoid adhesive external indicators and labels; they tend to get stuck.

When using containers in loads with wrapped items, always place the containers on the bottom shelves, because they will develop condensate that could drip, potentially compromising the sterile integrity of the wrapped items. Do not stack containers unless the manufacturer expressly permits it. Stacking could interfere with air evacuation, steam penetration, and drying.

A Primer on Steam Sterilization
After you've decontaminated and packed instruments, it's time to sterilize them. There are many ways to sterilize items. The most common by far is steam.

As this is considered to be the most effective form of sterilization, most facilities use it for all items that can withstand the temperatures and pressures of steam sterilization without damage.

Steam offers many advantages. It can be heated to temperatures hot enough to kill spores, the most resistant of micro-organisms. It's also non-toxic, freely available and fairly easy to control.

It's important not to take steam for granted, however; to steam sterilize effectively, you need to understand how to create "quality steam" and how to make sure the steam reaches all surfaces of the items being sterilized.

Quality steam
To be an effective sterilant, steam needs three qualities:

First, the steam needs to be hot enough to kill spores, the toughest micro-organisms.

Steam sterilizers heat steam in the same way pressure-cookers do; they continually feed steam from the boiler into the pressure vessel; as the atmospheric pressure increases, the temperature rises. In time, the steam becomes hot enough to kill spores. This is rarely a problem with most modern steam sterilizers.

Steam also needs to be relatively "dry." If the steam contains too much water, condensation collects and pools on the instruments inside the pack, a phenomenon known as "wet packs." This problem is not uncommon.

Ideally, steam should consist of two to three parts by weight of saturated water to 97 to 98 parts by weight of dry saturated steam.

Too-wet steam generally results from three things:

  • An abnormally high level of water in the boiler.
  • Poor maintenance of the steam distribution lines, which could cause condensation in the lines.
  • Failure of the sterilizer jacket trap. The sterilizer chamber is enclosed in a metal jacket into which steam is introduced so as to maintain a consistently, warm chamber wall. If this system fails, the chamber wall will cool down, causing more condensate inside the chamber when steam is introduced.

Steam also needs to be "clean." If there are contaminants in the boiler water and they make their way to the pressure vessel, impurities could collect on or in sterile packages.

Prevention is the best medicine. Get your sterilizers on a regular preventive maintenance program which includes checking of all the steam lines, filters, baffles, traps, drain lines, etc. Occasionally in the case of contaminated steam it's necessary to flush lines to rid them of debris.

Even perfect steam does not ensure effective sterilization. It is also important to make sure the steam reaches all the surfaces of the items you are sterilizing. One key to this is removal of all the air from the sterilizer chamber. Air acts as an insulator around the items and prevents the steam from achieving full contact. It also prevents the steam from heating up to spore-killing levels.

Sterilizers accomplish the task of removing the air in three ways:

  • Gravity. This is the simplest but also the least efficient method. Gravity displacement sterilizers incorporate a drain, usually at the lower front end of the sterilizer. As steam enters at the top, it gradually forces air out at the bottom through the drain. As the steam hits the objects to be sterilized, it gives up its latent heat to the objects and collapses back to water. The condensate must be able to drain out of the items and out the drain at the bottom. When this process is finished, a trap in the drain closes and the cycle time begins. A typical cycle takes 30 minutes at 250 degrees F, or 15 to 25 minutes at 270 degrees F. After the cycle is complete, filtered air enters the chamber and steam is evacuated until the pressure in the chamber reaches atmospheric pressure.

What You Need to Know About Flashing

Flash sterilization, or steam sterilization with no drying or packaging, may be useful in situations where you need rapid OR turnover. But it is critical to do it properly. Here are tips on how.

Decontaminate Thoroughly
In Central Service departments, the decontamination activity appropriately takes place in a negative pressure area physically separated from the prep, pack, and sterilization areas. But too often, flash sterilization takes place in a busy, patient-care area, by staff that is not trained in proper cleaning techniques.

If you are routinely flash sterilizing complete sets between cases (which I do not recommend; it's better and safer to take the time to sterilize wrapped packs), you must dedicate a secured place and trained staff for decontamination. Make sure your staff understands how to separate clean instruments from dirty ones, disassemble and reassemble complex instruments, and properly use washer/decontaminators and ultrasonic equipment. Make sure a trained person supervises this activity.

Don't Overload
If you can sterilize a single surgical instrument in three minutes, you may think, why not sterilize two? Or three? Or perhaps an entire set?

The kinetics of effective steam sterilization require the steam to condense on the surfaces of the items being sterilized, where it gives up its latent heat to the object and then evaporates. It's this condensation and the associated heat transfer that allow items to be heated much more rapidly in steam than in dry heat. This evaporation creates a temporary vacuum that pulls fresh steam to the surface where more heat is transferred until the steam and the object being sterilized are the same temperature. This is called the conditioning phase.

The length of the conditioning phase varies depending upon the amount of metal mass in the load, the source and quality of steam, and the type of cycle used (gravity, pre-vacuum, or steam-flush pressure pulse [s-fpp]).

If you load the sterilizer with too many instruments, or instruments that are too heavy, you will prevent this transfer of energy from occurring in the short amount of time that a typical flash cycle usually takes. Therefore, keep sets simple and the instruments spaced so that steam reaches all surfaces uniformly.

Do not attempt to flash power tools — there are too many hidden crevices and places to trap air. You can flash lumened instruments in gravity cycles for 10 minutes, pre-vacuum cycles in four minutes, and s-fpp cycles in three minutes. Make sure you open all hinged instruments and ratchets, disassemble all complex instruments, and place instruments with concave surfaces so that the surface does not pool water or trap air.

Never flash sterilize implantables. They need to be quarantined until you obtain the results from the biological monitoring of the sterilization cycle.

Transport with Care
Because the sterilized items are hot and wet when the sterilizer door is opened, they are extremely susceptible to contamination by airborne particles. For this reason, you must protect these items from the time you open the door and as they travel from the sterilizer to the operative field. The distance from the sterilizer to the operative field should be as short as possible. Ideally, the sterilizer should be in the same room. Under no circumstances should you transport an open tray down corridors-not even so-called "sterile" corridors.

If the sterilizer is in another room, protect the top and bottom of the tray from airborne contamination while en route to the sterile field. There are several ways to do this.

The least optimal option is to cover the tray with a sterile towel. If you use this option, have the sterile towel ready when the sterilizer door is opened. The towel should be large enough to cover both the top and bottom of the tray. Do not simply toss the towel over the sterilized items, rather, place the tray on one end of the towel and fold the other end over so that both the top and bottom of the tray are covered.

Another solution is to place a tray cover on its edge during the cycle and then simply use it to cover the tray before removing it from the chamber.

A better solution is to single-wrap the items and use a vacuum assisted cycle for four minutes or s-fpp cycle for three minutes.

The best solution is to use a flash approved container in a vacuum assist or s-fpp cycle according to the manufacturer's recommendations. Under no circumstances should you use a sterilization container in a gravity cycle unless and until you test your heaviest load with appropriate biological, enzyme, or chemical integrators placed inside the container wherever air can be trapped.

Final Thoughts

  • Use mesh bottom trays rather than solid or perforated trays. They sterilize and drain better.
  • Do not attempt to cool down hot instruments out of the flash sterilizer by pouring sterile water over them. If handling hot instruments is a major problem, I recommend having a dedicated basin filled with sterile water handy so that the hot instrument can be dipped and then dried with a sterile towel.
  • Do not "crack-the-door" and leave it open after the cycle to allow the contents to cool down. This allows the sterile hot air to rush out of the chamber and lets potentially contaminated cool air rush in over the hot, wet instruments. Always cover and bring out the instruments immediately after you open the sterilizer door.
  • Do not use flooding gravity flash sterilizers for flashing. The debris that is in suspension can reattach to the instruments as the water is drained. The hot steam then cooks the debris onto the instruments, which compounds the problem.
  • Have enough instruments so that you do not have to rely on flash sterilization for routine sterilization between cases. Though this may require an initial capital outlay, it will pay off in the long run. Instruments will last longer and need to be repaired and replaced less often.
  • Buy state-of-the-art sterilizers. Avoid gravity displacement sterilizers.
  • Develop protocols to ensure proper cleaning and decontamination, inspection, and arrangement of instruments into approved sterilizing trays or containers prior to sterilization.
  • Ensure that the physical layout of the department or work area ensures the direct delivery of sterilized items to the point of use.
  • Develop, follow, and audit procedures to assure aseptic handling and personnel safety while transporting sterilized items from the sterilizer to the using area.

Alternatives to Steam

Outpatient surgical facilities are now hosting more and more complex procedures, and consequently, surgeons are using many new surgical instruments that can't be sterilized with steam.

To handle these sensitive instruments, low-temperature terminal sterilization has taken on a larger role. In this article, I'll briefly explain the mechanism of low-temperature sterilization processes.

EtO Sterilization
Ethylene oxide, or EtO, kills microorganisms by replacing available hydrogen atoms with alkyl groups. It is very effective and compatible with a wide range of materials. It has excellent penetration characteristics and is available in equipment sizes from table-top to large floor loaders. However, EtO has declined in popularity in recent years, for three reasons:

  • Expense. EtO typically gets mixed with other gases for stability. One of the most popular mixers, CFC-12, is being phased out because of environmental concerns, and being replaced by more costly HCFC;
  • Safety. Breathing EtO vapors has been linked to serious health problems. It's also explosive and flammable. To use it safely, facilities have had to take expensive measures such as installing engineering controls, using ventilators, training staff, etc.
  • Speed. EtO requires a long aeration process to purge chemicals that could be harmful to the patient. The entire process takes anywhere from an hour or two up to 24 hours.

That said, EtO does have properties that make it an important and vital part of the sterilization armamentarium. It can penetrate a wide variety of packaging materials to destroy microorganisms and then diffuse away from the product, eliminating sterilant residue. A lot of facilities still use EtO, although perhaps not as often as they once did.

The EtO sterilization process comprises five distinct phases:

  • temperature/humidity conditioning;
  • gas introduction to a predetermined concentration;
  • exposure;
  • exhaust; and
  • Purge/aeration/detoxification.

A few notes: The higher the temperature, the more effective the sterilization process. At 55ºC/131ºF, the sterilization portion of the process requires anywhere from one to two hours. At 37ºC/99ºF it can take as long as 4.5 to 5.5 hours.

  • Moisture vapor is key to the efficacy of EtO. It doesn't work on desiccated products.
  • Aeration, which eliminates EtO residue from the product and the packaging, can take place either in the sterilizer or in a heated cabinet designed for this purpose. The time required depends on the materials being degassed. Metal instruments require little or no aeration, while polyvinyl chloride (PVC) and rubber can take as long as 24 hours.
  • EtO sterilizers come in several different versions. Special packaging is often necessary. For more on EtO sterilizers, see Outpatient Surgery, March 2001.

Gas Plasma Sterilization
Plasma is the fourth state of matter as distinguished from solid, liquid, or gas. It can be produced either through the action of very high temperatures or by strong electric or magnetic fields.

The Sterrad system by Advanced Sterilization Products uses an aqueous solution of hydrogen peroxide (H[2]O[2]) that is vaporized in a deep vacuum chamber containing the items to be sterilized. The H2O2 is toxic and exerts its own lethal effects, but its real purpose is to serve as a precursor for the generation of the plasma. The system then introduces a radio frequency that creates an electrical field, which turns the H2O2 vapor into plasma. The plasma releases free radicals that collide or react with and kill harmful organisms.

Here's how Sterrad gas-plasma sterilization works. First, you place the items to be sterilized in a high-vacuum chamber. The system vaporizes an aqueous solution of 58% hydrogen peroxide (H2O2) and injects it into the chamber so the devices are enveloped in H2O2 vapor. The vapor kills microorganisms and acts as an oxidizing seeding agent and a precursor for the plasma. After the H2O2 vapor has diffused throughout the load, the chamber pressure falls to allow for the generation of gas plasma. The system induces the plasma state by applying radio frequency energy into the chamber. The plasma generates unstable molecules called free radicals that collide with and kill micro-organisms. Once the free radicals have reacted, they recombine to form water vapor, oxygen, and other non-toxic byproducts.

Three notes about working with gas plasma:

  • Although oxidants are more chemically reactive than alkylating sterilants, making them more effective at low temperatures, they are also less likely to penetrate all portions of the objects being sterilized (especially areas such as long, narrow lumens).
  • Check with the manufacturer prior to using metal trays with this system to make sure they're compatible.
  • No packaging or item being sterilized can contain cellulosic materials that might absorb the sterilant. If absorption occurs, the cycle will abort.
  • The H[2]O[2] solution is packaged in a sealed cassette that the operator places into a slot in the sterilizer, where it advances automatically into position. One cassette lasts for approximately ten 90-minute cycles. The sterilant is depleted as it sterilizes, and there is a risk of not having enough for a particularly challenging load. The system will abort if this happens.

Peracetic-acid sterilization
Steris Corporation introduced peracetic acid a decade ago as the first alternative to glutaraldehyde for sterilizing endoscopes; its Steris System 1 provides rapid, automated, low-temperature, standardized liquid chemical sterile processing of endoscopes at or near the site of patient use.

Here's how it works: After manually cleaning the endoscope, you place it in the unit and add the sterilant solution, a 35-percent peroxyacetic-acid concentrate. The system dilutes the concentrate to 0.2% peracetic acid. It then heats the solution to about 50-56 degrees C for 12 minutes and allows it to contact all external and lumen surfaces of the endoscope. Four separate sterile water rinses follow, concluding with a sterile air purge. Total sterilization time is about 30 minutes. This means if you have 30 minutes between cases, or if you can schedule cases so that every other one is more than 30 minutes apart, you can have a sterile instrument for each case by only having two instruments in stock.

Dry heat Certain items cannot be sterilized with any of the above methods. They include:

  • non-aqueous liquids or semi-solids such as glycerin, oils, petroleum jelly, and waxes;
  • powders such as talc and sulphonamides;
  • glassware;
  • stainless steel, particularly instruments that have facing surfaces that are difficult to reach with steam and instruments that dull and/or stain when subjected to steam and its impurities; and,
  • water and aqueous solutions, like IVs.

For these items and others, (including reusable needles), the sterilization method of choice is dry heat.

Although dry heat is the only acceptable method for items like the ones above, it's generally a poor choice for items that can be sterilized in another way. Dry heat requires temperatures of at least 170 degrees C (338 degrees F), and so can char some items.

Traditional dry heat, which works like a convection oven, is quite slow. An exposure time of 60 minutes at 160 degrees C (320 degrees F) for dry heat is approximately the equivalent of 15 minutes at 120 degrees C (248 degrees F) for steam.

Newer dry heat sterilizers work faster, but the items you sterilize must be even more durable; they achieve the speed in part by raising the temperature to as high as 210 degrees C (410 degrees F). Items with very thin sharp edges, like cataract knives, will dull when exposed to heat such as this.

Arranging items in a dry heat sterilizer very carefully. For dry heat to work it must be able to affect all surfaces that could harbor microorganisms. It's important to maximize the exposed surface for items in the sterilizer. For example, before sterilizing talc, you must use a large pouch and spread out the talc as thinly as possible. If you are sterilizing a dressing, you need to unroll it.

Since there is no commercially available test pack for monitoring dry heat sterilizers, I recommend designing one that is representative of the type of dry heat sterilization you will be doing. Suppose the only items you dry heat sterilize are single-use portions of talc in nylon pouches. Once a week, insert a suitable biological indicator in the pouch with the talc and record the results. I know of only one type of biological indicator that is available for dry heat sterilization. These are filter paper strips impregnated with Bacillus subtilis var. niger. These strips come packaged in glassine envelopes. Their main disadvantages are that the paper and glassine become marginal at temperatures above 400 F, they require aseptic culturing techniques, and it takes a long time to get the results.

Measuring and recording the physical parameters of your desired cycle is extremely important in dry heat sterilization. Modern table-top dry heat sterilizers have incorporated improved heat transfer methods using mechanical air circulation, high speed laminar flow, and higher process temperatures.

Alternative Packaging Options Packaging options designed for steam often are not appropriate for alternative sterilization methods.

For both EtO and plasma, there are three options:

Special plastic peel pouches: These are typically made of Tyvek? on one side and a polyethylene/ polyester lamination on the othe. They are pricier than paper pouches and require special sealers. Paper pouches won't work in plasma sterilizers; cellulosic fibers absorb the sterilant and cause the cycle to abort.

Plastic bags: Pre-sterilization plastic bags are made of polyethylene that is at least 3 mm thick. They have a breathable patch (either circular or a strip) to allow the entrapped air to escape during the vacuum cycles. You can seal them with the same type of sealer as all-plastic peel pouches.

Rigid Containers: Only one container of which I am aware (Steri-Tite, Case Medical) is FDA approved for gas plasma sterilization. Other manufacturers claim that their boxes work in gas, but I would recommend verifying the claim prior to going live. Use your standard instrument sets and lots of biological indicators placed in all the hard-to-reach places within the container.

The two main packages for dry heat sterilization are paper or nylon film pouches and metal cassettes or containers. Pouches are normally used only for single instruments, small amounts of talc, or small treated dressings. Only use all-paper pouches specifically designed as sterilization pouches or all-nylon pouches.

If you are using a gravity displacement sterilizer, the most critical thing to remember is to position the items within the load so that both air and moisture can escape downward.

Vacuum Pump. More modern sterilizers evacuate all air from the chamber before allowing steam to enter. Without air to impede the process, steam can reach all the surfaces of the items much more rapidly-in three minutes, in some cases. However, if the pump is unable to remove all the air, or if air leaked or entrained into the load through faulty door or pump gaskets, the items can't be sterilized properly. This can occur when you shut the sterilizer down and allow it to cool; the door and vacuum pump seals shrink. If they are defective, they won't return to their original shape when you put the sterilizer online again, allowing air to leak into the chamber.

You can and should check your vacuum pump sterilizer anytime you shut it down with the Bowie-Dick test. See "Monitoring" for more.

A newer and more efficient type of vacuum sterilizer first allows some steam in to humidify and heat the load. Then it draws a vacuum. Today's vacuum sterilizers use several purges of steam and vacuum to enhance this effect. A pulsing pre-vacuum cycle is much more efficient at removing air and not as dependent on the positioning and makeup of the load.

Steam-flush pressure-pulse sterilizers (a system made popular by Joslyn Sterilizer, now Steris) use repeated sequences of steam flushes and pressure pulses to remove air from the chamber and the materials being processed.

Because these sterilizers operate at above atmospheric pressure throughout the entire cycle, the system is not susceptible to air leaks. Bowie-Dick type tests are not necessary.

Understanding Monitoring
For steam sterilization to be effective, the steam must contact every area of the items being sterilized with saturated steam that is at the right temperature, for an appropriate period of time. It's impossible to measure steam temperature in every package, but you can use mechanical, chemical, and biological monitors to measure conditions within the chamber.

Mechanical Monitoring
The most dependable method for understanding the events inside the sterilizer is monitoring the temperature and pres-sure during and after every load.

To measure temperature, older sterilizers have a liquid filled bulb and a capillary system connected to a mechanism that makes a tracing on a chart recorder. It's important to scrutinize and think about the somewhat complex information on the chart. Obviously, you want to know whether the sterilizer reached the desired temperature for the appropriate length of time. But also consider whether the sterilizer is providing signs that it is about to malfunction. For example, if the slope of the curve representing the time the sterilizer takes to come up to temperature is not the same, cycle after cycle, for similar loads, it may mean that the lint trap is becoming clogged, or that air is leaking into the chamber.

Newer sterilizers have electronic sensors directly connected to a control panel that gives a visual readout and record keeping in the form of a printed tape.

Either way, check the record carefully at the end of each cycle before removing the load.

Saturated Steam Temperature and Pressure


º F





Chemical Monitoring
Chemical indicators can help you detect potential sterilization failures resulting from:

  • incorrect packaging;
  • incorrect loading of the sterilizer; or
  • sterilizer malfunction.

A lot of facilities rely heavily on chemical monitoring, believing that it is highly dependable. Not so.

It is very helpful to have a chemical indicator on the outside of every package as a simple signpost that the item has been through a sterilization process. These indicators tell you almost nothing about what has happened inside the package, however.

Using indicators inside of packages, where they will give you useful information, is much more challenging. Remember, chemical indicators can only tell you if the area where they are placed received steam. For this reason, they are useful only if you place them within the package in a place where air can potentially be trapped.

For example, a chemical indicator inside a peel pouch inevitably rests against the paper side, an area very unlikely to trap air. A chemical indicator packaged with instruments in a mesh-bottom tray also tells you very little, since air is unlikely to be trapped here. An internal indicator on the top of a basin set, just under the wrap, is also a waste of time and money, since it will not tell you if the basin set was placed improperly on the sterilizer cart. The proper place, the only place where air can be trapped, is in the bottom of the basin set, preferably between the two basins in the towel used to keep the basins apart.

It is not necessary to place chemical indicators in every package; rather, use them intelligently in only those packages that represent a challenge to the sterilization cycle.

Also remember that not all chemical indicators are created equal. I recommend running both good and bad cycles with the indicators you are testing in various places within a variety of packages relative to what the product is designed to detect. Try to determine which indicators produce the most reproducible results.

If you have a pre-vacuum steam sterilizer, you must perform a Bowie-Dick type chemical indicator test whenever the sterilizer is shut down for any reason. When a sterilizer is shut down and allowed to cool, the door seals and vacuum pump seals shrink. If they are defective, they won't return to their original shape when the sterilizer goes back into service, allowing air to leak into the chamber. The steam will then carry the non-sterile air in the chamber into any packs that are in the chamber. The same problem can occur if your steam lines are leaky and pumping air as well as steam into the chamber.

The Bowie-Dick test can help you determine whether either problem is present. It uses an approximately 8" x 10" sheet of paper printed with an indicator ink pattern. Place it in a linen pack or in a test pack and run it through the sterilizer cycle alone in a pre-vacuum cycle. The ink should change color uniformly.

Biological Monitoring
Biological indicators represent the actual destruction of viable organisms. Standards-setting bodies such as AAMI and AORN as well as JCAHO recommend that you use biological indicators at least weekly in all sterilizers and in every load when implants are sterilized.

Biological indicators contain spores of organisms that exhibit high, stable, and reproducible resistance to the mode of sterilization you are monitoring.

Like chemical monitors, biological indicators only provide useful information if they are placed properly.

Keeping good records of your monitoring is an important element in any quality assurance program. Have a knowledgeable person review them regularly.