Correct loading and unloading of a sterilizer vital for sterilization, sterility maintenance

Chris Miller, PHD

Processing of instruments for reuse on another patient involves many steps. These may include holding, cleaning, rinsing, lubrication, corrosion reduction, drying, packaging, sterilization, drying, cooling, transport, storage, distribution, and monitoring. Some steps are discussed more frequently than others, but all are important. The two aspects of sterilization that will be emphasized here are loading and unloading of the sterilizer.

All surfaces of an item to be sterilized must come into direct contact with the sterilizing agent for the complete exposure time. This is true for steam, unsaturated chemical vapor and dry-heat sterilization.

Thus, it is important not only to use the proper packaging materials and techniques, but also to load the sterilizer correctly. Sufficient space must occur around the packages within the load to facilitate air removal in steam sterilizers as well as the circulation of the sterilization agent in all sterilizers. In steam sterilizers, the air in the chamber and inside packages must be replaced with steam to achieve sterilizing temperatures. If pockets of air exist, as can occur with improper loading of the sterilizer chamber, sterilization will not be achieved at those sites.

Follow the loading instructions provided by the sterilizer manufacturer. If such instructions are not available, follow these general guidelines.

Minimum contact should occur between the packages or cassettes in the sterilizer chamber. The general rule-of-thumb is to place items on their edge and not overload the chamber. Some sterilizers come with loading racks or trays that have "dividers" to keep packaged items apart. The separation that is created naturally when items are placed on their edges provides a more ready assess of the sterilizing agent to all surfaces of the package.

A single layer of packages may be used, but do not stack packages or cassettes one upon the other. The weight of each on the one below minimizes the space between each and reduces access to the sterilizing agent. Do not tie groups of packages together in the chamber because this also limits access to the sterilzing agent.

The paper/plastic peel pouch is a popular sterilization packaging material. The sterilizing agents of steam or chemical vapor enter the packaging through the paper side of the pouch, and the plastic side usually is impermeable. Thus, when processing multiple paper or plastic pouches, place them on their edges with the paper of one pouch next to the plastic of the adjacent pouch (i.e., paper to plastic).

If instrument packages are dated and/or marked with a sterilization-control number, and this labeling is performed before processing the packages through the sterilizer, label the packages just before the sterilizer is loaded. Prelabeling before this time enhances the risk of someone mistaking the labeled - but unprocessed - packages for sterile items.

The sterility of instruments is to be maintained until the instruments are delivered to chairside for use. Several things can challenge this sterility maintenance. Sterilized-instrument packages should be handled as little as possible. Wet packages that exist at the end of steam-sterilization cycles should not be handled at all. The paper on the paper bags, paper wrap or paper/plastic pouches will tear very easily when wet and may draw through (wick) microbes that contaminate the package surface.

Some steam sterilizers have an automatic dry cycle while others will indicate that drying is to be achieved by opening the door about half an inch after the pressure equalizes and letting the items sit inside the chamber for 30 to 60 minutes. Be careful when opening the steam-sterilizer door. Some steam may rise from the top and hot water may drip from the bottom of the chamber opening. Packages are dry at the end of the unsaturated chemical-vapor and dry-heat sterilization cycles. Dry-cooled packages should be removed carefully from the sterilizer or sterilizer tray by gloved hands and not by tongs. Tongs may more easily rupture the packaging material.

If it is necessary to process an instrument through a OflashO (short time at high temperature) sterilization cycle, special procedures must be used at unloading. Flash sterilization involves processing an unpackaged item that will be used immediately.

A written protocol should be developed and followed that limits the potential for contamination of the unwrapped instrument on its trip to the patient. The unwrapped, processed item should be touched only with sterile tongs, towels or gloves when unloaded from the sterilizer or sterilizer tray. It should be placed in a sterile container or held in a sterile towel for transport to the patient for immediate use. Remember that the item likely will be hot and may develop condensation as it cools outside the sterilizer.

In summary, proper loading of a sterilizer facilitates circulation of the sterilization agent and helps assure that all items are exposed to the proper temperature for the right amount of time. Proper unloading of the sterilizer helps assure the maintenance of sterility.

Chris Miller is director of Infection Control Research and Services and professor of oral biology at Indiana University.