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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