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Steam SterilizationMay 17, 2011
Steam sterilization is a process of thermal sterilization employing highly pressurized saturated steam in a chamber [autoclave]. Steam sterilization is a widely employed sterilization process. The basic principle of operation is that the air in the sterilizing chamber is displaced by the saturated steam, achieved by employing vents or traps in gravity-displacement cycles or by active removal in dynamic-air-removal cycles. In order to displace air more effectively from the chamber and from within articles, the sterilization cycle may include air and steam evacuation stages. The design or choice of a cycle for given products or components depends on a number of factors, including the heat lability of the material, knowledge of heat penetration into the articles, and other factors described under the validation program (see above). Apart from that description of steam sterilization cycle parameters, using a temperature of 121C, the F0 concept may be appropriate. The F0 , at a particular temperature other than 121C, is the time (in minutes) required to provide the lethality equivalent to that provided at 121C for a stated time. Medical instruments and their sterilization trays need to be validated both with respect to cleaning effectiveness and sterilization. Most commonly companies submit validation data performed in accordance with ST79. The key component of a persuasive validation is a thorough assessment of worst case conditions. Gibraltar Laboratories recommends that worse case be defined not only with respect to the article subject to the validation but also with respect to the steam sterilizer under maximal and minimal load configurations. This is necessary for each sterilization cycle type, namely gravity-displacement and dynamic-air-removal [pre-vacuum]. Accordingly one selects the instrument in the case that is judged to be the most difficult to sterilize. This instrument is then challenged with artificial soil and highly resistant biological spores. The tray is wrapped in accordance with ST79 and placed in the steam sterilizer at its cold spot. The cold spot is determined by thermal mapping with NIST traceable thermocouples. Three half-cycles are performed at 134C. In order to pass the validation all of the biological spores must be killed and the instrument or its tray must be completely dry.
A related and additional validation involves cleaning instruments that have been challenged. For example one can challenge with oils, protein, blood, endotoxin, particulates and cleaning agent. Cleaning is performed using one or both of a defined automated cleaning process or defined manual cleaning process. Successful cleaning is demonstrated by the removal of the challenge and absence of particulates and cleaning agent.