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
- How to Package Instruments Effectively
- A Primer on Steam Sterilization
- Understanding Monitoring
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.
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.
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.
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.
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.
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.
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.
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.
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 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.