![]() ![]() 835 Sterilizer vacuum performance is acceptable if the sheet inside the test pack shows a uniform color change. 833 These devices are “designed to simulate product to be sterilized and to constitute a defined challenge to the sterilization process.” 819, 834 They should be representative of the load and simulate the greatest challenge to the load. Smaller disposable test packs (or process challenge devices) have been devised to replace the stack of folded surgical towels for testing the efficacy of the vacuum system in a prevacuum sterilizer. Air that is not removed from the chamber will interfere with steam contact. 813, 819 The test is used each day the vacuum-type steam sterilizer is used, before the first processed load. The test pack should be placed horizontally in the front, bottom section of the sterilizer rack, near the door and over the drain, in an otherwise empty chamber and run at 134☌ for 3.5 minutes. A commercially available Bowie-Dick-type test sheet should be placed in the center of the pack. The Bowie-Dick test is used to detect air leaks and inadequate air removal and consists of folded 100% cotton surgical towels that are clean and preconditioned. The advantage of using a vacuum pump is that there is nearly instantaneous steam penetration even into porous loads. ![]() ![]() 831, 832 The high-speed prevacuum sterilizers are similar to the gravity displacement sterilizers except they are fitted with a vacuum pump (or ejector) to ensure air removal from the sterilizing chamber and load before the steam is admitted. This point is illustrated with the decontamination of 10 lbs of microbiological waste, which requires at least 45 minutes at 121☌ because the entrapped air remaining in a load of waste greatly retards steam permeation and heating efficiency. For gravity displacement sterilizers the penetration time into porous items is prolonged because of incomplete air elimination. The gravity displacement autoclaves are primarily used to process laboratory media, water, pharmaceutical products, regulated medical waste, and nonporous articles whose surfaces have direct steam contact. In the former, steam is admitted at the top or the sides of the sterilizing chamber and, because the steam is lighter than air, forces air out the bottom of the chamber through the drain vent. The two basic types of steam sterilizers (autoclaves) are the gravity displacement autoclave and the high-speed prevacuum sterilizer. At constant temperatures, sterilization times vary depending on the type of item (e.g., metal versus rubber, plastic, items with lumens), whether the item is wrapped or unwrapped, and the sterilizer type. Recognized minimum exposure periods for sterilization of wrapped healthcare supplies are 30 minutes at 121☌ (250☏) in a gravity displacement sterilizer or 4 minutes at 132☌ (270☏) in a prevacuum sterilizer (Table 7). These temperatures (and other high temperatures) 830 must be maintained for a minimal time to kill microorganisms. The two common steam-sterilizing temperatures are 121☌ (250☏) and 132☌ (270☏). Specific temperatures must be obtained to ensure the microbicidal activity. 813, 819 Pressure serves as a means to obtain the high temperatures necessary to quickly kill microorganisms. ![]() The ideal steam for sterilization is dry saturated steam and entrained water (dryness fraction ≥97%). Thus, there are four parameters of steam sterilization: steam, pressure, temperature, and time. The basic principle of steam sterilization, as accomplished in an autoclave, is to expose each item to direct steam contact at the required temperature and pressure for the specified time. ![]()
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