INFECTION CONTROL 14

Sterilization Control

•     A chemical monitor is an object that is treated with material that changes its characteristics when sterilized. This may be in the form of special ink that is impregnated into paper strips or tape and placed on the outside of the package, or it may be a substance that is incorporated into a pellet contained in a glass vial

•     The chemical responds to conditions such as extreme heat, pressure, or humidity but does not take into consideration the duration of exposure, which is critical to the sterilization process

•     Another monitoring method used to evaluate the steam sterilizer is the combined temperature time graphs that are installed within the control panel of the sterilizer. These graphs provide a permanent written record of all loads that have been processed

•     The surest way to determine the sterility of given items is with the use of biologic controls. A strain of a highly resistant, nonpathogenic, spore-forming bacteria contained in a glass vial or a strip of paper is placed in the load of goods to be sterilized. For steam sterilization, the dry spores of the bacteria Bacillus stearothermophilus are used. The gas sterilization process uses the bacterium Bacillus subtilis. The vial or strip is recovered at the end of the sterilization process and cultured. This process is time consuming and the results method of testing the efficacy of a sterilization process. Biologic controls should be administered at least once weekly. If feasible, they should also be used whenever an artificial implant or prosthesis is sterilized and the item withheld from use until the results are known to be negative.

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INFECION CONTROL 13

TYPES OF STERILIZERS

Gravity displacement sterilizer  The gravity (or “downward”) displacement sterilizer uses the principle that air is heavier than steam. Within the sterilizer there is an inner chamber where goods are loaded and an outer jacket type chamber that ejects steam forcefully into it. Any air in the inner chamber blocks the passage of pressurized steam to the surface of the goods and thus prevents sterilization. All the air must be removed because every surface of the supplies must be exposed to the pressurized steam to ensure sterilization. Therefore, the sterilizer is constructed in such a way that air is pushed downward by gravity (hence the name “gravity displacement sterilizer”).

Prevacuum sterilizer  The prevacuum sterilizer does not rely on gravity to remove air from the inner chamber. Instead, the air is pulled out of the chamber, which creates a vacuum in the chamber. Steam is injected into the chamber to replace the air. This type of sterilizer offers greater steam penetration in a shorter time than the gravity displacement sterilizer.

Flash sterilizer  The flash sterilizer has traditionally been used in the operating room and in other areas of the hospital to quickly sterilize items that are unwrapped. It has been common practice to flash sterilize any instrument that had become contaminated during surgery.

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INFECTION CONTROL 12

The Cycle of Operation

For a high-vacuum/high-pressure sterilizer, this can be summa­rized as follows:

      After loading the chamber and closing the door. The stages of autoclaving are:

•     Stage-1 Pre-vacuum—Air removal. The air is removed from the chamber by a vacuum pump and controlled steam pulsations. The vacuum achieved should be in the order of 0.5 mm Hg absolute (0.066 to 0.132 kPa).

•     Stage-2 Sterilization—Hold period at operating temperature. Steam is admitted to the chamber and when all parts of the load have reached a temperature of 134 degree C this is maintained for 3.5 minutes

•     Stage-3 Drying—Achieved by an adequate post vacuum, checked periodically by a test pack of towels which when removed from the sterilizer, unfolded and allowed to cool are not damp

•     Stage-4 Breaking the vacuum—Air replacement. This should be completed within 3 minutes, through a glass fiber or ceramic type filter

      The chamber is unloaded and the packs marked with the batch number of that particular load. Preset trays should have a water repellent or plastic dust cover applied if they are to be stored for more than a few hours. This cover should be applied only after the trays have cooled off.

      The recommended combination of time and temperature varies, and for instruments which can withstand moist heat under pressure the following cycles are recommended:

•     134°C (30 lb/in2) for a hold time of 3 minutes

•     121°C (15 lb/in2) for a hold time of 15 minutes.

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INFECTION CONTROL 11

 Steam is the gaseous form of water. If it is to sterilize effectively, which means killing all spores:

• It must be at an appropriate temperature (which implies an appropriate pressure).

• It must be saturated with steam.

• Thus not be mixed with air, so it must displace all the air in the chamber of the autoclave.

• And, it must reach all parts of the load. If it contains droplets of water, it will soak into porous materials.

If no air is discharged, the bottom of the chamber may be much cooler than the top.

As soon as the chamber of an autoclave is full of steam at the desired temperature and pressure, it must be held there for a critical time—the holding time. The standard holding time is 15 minutes, at 121 degree C, but you may need to vary it.

Single walled autoclaves are strong metal chambers with water in the bottom, like large pressure cookers. They have several disadvantages.

This is by far the most efficient method of sterilization for materials that will stand up to heat and moisture.

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