STERILE PROCESSING UNIVERSITY
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Today there are many choices for sterilization in the healthcare facility:
This In-service will focus on steam sterilization. Steam should always be the preferred method of sterilization unless otherwise directed by the manufacturer of the device. In addition, the technician should always follow the sterilizer manufacturer's directions for operating the sterilizer. Sterilization equipment should not be used unless the technician is competent in its use. For sterilization, items must first be scrupulously cleaned! Sterilization begins in the decontamination area.
For steam sterilization, the phases of the sterilization cycle are:
time varies with the temperature. The lower the temperature the longer
the exposure time; the higher the temperature the shorter the exposure
time. There are special cycles for liquids; liquids require a gravity
displacement cycle with slow exhaust to prevent explosion of the bottles.
There are two basic types of sterilizers; pre-vacuum (also known as high vacuum) and gravity displacement. The pre-vacuum sterilizers can also operate as gravity displacement. The usual cycle for pre-vacuum sterilizers for wrapped items is:
The drying time is dependent on your facility, the age of the sterilizer and the load contents.In gravity displacement sterilizers the usual cycle is:
It is important to remember that the greatest resistance to steam sterilization is removal of air! Therefore, the pre-vacuum sterilizer is more effective since it is more efficient at air removal.
How Steam Enters the Chamber - The steam is generated in a boiler located in Engineering (unless the facility is using a self generating steam sterilizer). The steam travels through high pressure steam lines to Sterile Processing. The steam enters the sterilizer from the top of the jacket which surrounds the chamber. The jacket provides strength to the chamber and insulates the chamber preventing the formation of condensate. As long as the steam supply is "on", there should be steam in the jacket and heat inside the chamber. (Most sterilizer manufacturers require that there be 60-80 pounds of steam pressure in the steam supply line. There is a gauge behind the sterilizer to record the steam line pressure.) The steam remains in the jacket, ready to be used when a cycle is started. When a cycle is started, the steam enters the chamber from the back through a baffle plate. This plate disperses the steam throughout the chamber. The air inside the chamber and packs is pulled in through a vacuum (in pre-vacuum sterilizers) or pushed out by the steam through gravity pull until all the air is removed. The steam continues to flow into the chamber and out through the chamber drain line (located on the bottom of the chamber, usually in the front). The steam continues down the drain line to the steam trap (also known as thermostatic valve). This valve remains open as long as the air is passing by it. However, once the valve senses steam passing by, the valve closes; this permits the steam to now build up inside the chamber. The steam then enters the packs. Once the packs are heated up and saturated with steam, the sterilizer starts timing the cycle. The timing is the "exposure or sterilization" time selected. This is the time when the microorganisms are being killed and is the most critical part of the cycle. When the exposure time is completed, the steam trap valve opens and the sterilizer exhausts the steam through the steam trap. Then the drying phase starts.
There are three main phases to steam sterilization:
The minimum exposure times, temperatures, and pressures for steam sterilization of wrapped items are as follows:
are minimum exposure times. The device manufacturer's written instructions
for exposure time and other parameters should always be followed. Any
exposure time less than the minimums should be questioned.
Steam quality - The quality of the steam supplied to the sterilizer is important to successful sterilization and effective drying. Steam quality is a measure of the relative dryness of the steam. Ideally, the incoming steam should be at least 97% dry saturated steam and at most 3% entrained water (AAMI ST79:2006). However, the moisture content of steam is important to the transfer of heat to items being sterilized. When items are placed inside the sterilizer, they are at room temperature (cool). When the hot steam makes contact with the cool items, condensation forms and energy (in the form of heat) is released, heating up the packs. Therefore, steam sterilization occurs by condensation.
"Superheating" of steam occurs when "saturated steam at any given temperature is subjected to a higher temperature . . . This occurs when heat is added to dry steam in the absence of water" (Perkins, 1982). In other words, the steam is "dried out." Without the moisture, the effect is that of dry heat sterilization, which not only can overheat the materials but also could result in ineffective sterilization.
to occur, the steam must make direct contact with all surfaces of the
device. Air is an enemy to the steam sterilization process because air
and steam do not mix. Therefore, it is essential that all the air be removed
from the chamber and packages. If air is entrapped in a package, the steam
will not be able to get inside (think of the concept that "no two
objects can occupy the same place at the same time"). Complete air
removal is important because air will interfere with steam contact with
the device. In a pre-vacuum cycle, the sterilizer draws one or more vacuums;
i.e., a pump "sucks out" the air from the chamber and the packs.
After air removal, the steam heats up the load to the temperature set
on the sterilizer. The steam transfers its latent heat energy to the items
inside the sterilizer. When this energy transfer occurs, the steam condenses
and becomes water.
Drying is critical to sterility maintenance. If packages are still moist when the sterilizer door is opened, bacteria can land on the packages and "wick" or travel inside the package. Drying time depends on several factors:
Regardless of the method of air removal, the air and steam exit through the chamber drain, a small opening usually located in the front of the sterilizer chamber on the chamber floor. A basket inside the drain collects lint and other debris. This basket must be cleaned out daily (by flushing it with running water or using a brush to remove the debris) to prevent clogging of the drain line. A clogged drain line can contribute to wet packs.
Wet Packs - Wet packs represent one of the greatest problems in sterility maintenance. Both AORN and AAMI do not the use of an item that is wet at the end of the steam sterilization cycle, even if it is inside a rigid container (AAMI ST79:2006; AORN, 2006). Wet packs can be caused by a number of problems, including:
Most CS/SPDs are faced with heavy and/or multi-level sets, which make drying difficult. The use of rigid container systems and heavy wrapping materials can also impede drying. It is the responsibility of the facility to ensure that sets and other packaged items can be dried after sterilization in the sterilizers being used. The heaviest sets should be selected and then sterilized, dried, and cooled. The sets should then be opened and inspected for moisture on the instruments, a wet or moist towel (if used inside the set), or visible water. None of these scenarios is acceptable. If a problem is noted, the first step is to check the configuration of the set (i.e., how the instruments are arranged in the set). If the instruments are well distributed within the set, then the next thing to try is preconditioning of the load. Preconditioning is done by placing the load in the sterilizer, closing the door, and waiting 10 to 15 minutes before initiating the cycle. (An egg timer can be used as a reminder to start the cycle.) The preconditioning process heats up the instruments (from the jacket heat in the sterilizer) and reduces the amount of condensate formed. Another thing to try is to extend the drying time of the cycle in 10-minute increments (unless the drying time is already set at 30 to 40 minutes). If these procedures do not solve the wetness problem, then it will be necessary to divide the set into smaller sets. The testing should be documented (type of set tested, date of testing, test results, and name or other identifier of the person who performed the testing). Repeat testing is not required unless changes are made to the set.
the Sterilizer - When loading steam sterilizers, instrument sets in
mesh-bottom pans or in perforated metal trays should be placed flat
on the sterilizer rack. The mesh bottom of the pan or the perforations
in the tray permit air removal and steam penetration in this position
(provided that the perforations are large enough). Instrument sets in
solid-bottom Mayo trays should be tilted on their edge (side) to permit
condensate to run off. All items should be loosely loaded. Multiple similar
items (e.g. towel packs) should be loaded so you could put your fist between
the packs. In mixed loads containing basins and line packs, place the
line items on the top shelf and metal items on bottom to prevent condensate
from over wetting packs which will interfere with drying. Any item that
can retain moisture (e.g. basin) should be tilted on its side to permit
the condensate to run off.
should be placed on their side to facilitate air removal (through the
folds) and steam penetration; they should not be placed flat. In the proper
position, the folds of the textile items should be vertical in relation
to the cart. In a mixed load (textile items and metal goods), the textile
packs should be placed on the top shelves and the metal instruments on
the lower shelves. If the textile packs are placed on the shelf below
the metal instruments, they could become wet. Basin sets or other devices
that can collect and retain water should be tilted on their sides.
Steam sterilization is a major responsibility of the sterile processing
technician. The sterilizer operator must be knowledgeable in all phases
of the steam sterilization cycle and how to monitor the process.