The Principles of Medical Device Decontamination

Monitoring Sterilization Processes

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Introduction

Medical Devices which are required sterile in use should be sterilized in a validated process. There are several standards which describe the development, validation and routine control of common sterilization processes using moist heat, ethylene oxide, low temperature steam with formaldehyde and irradiation. There is also a generic standard for the development, validation and routine monitoring of a sterilization process not covered by a specific standard. Having validated a sterilization process using a defined documented procedure (HTM 01-01 1 ), periodic tests should be carried out (e.g. daily, weekly, quarterly) to confirm ongoing process efficacy. In addition, routine monitoring must be carried out to ensure each production cycle has been carried out satisfactorily. Published standards and national guidance provide schemes indicating what tests should be carried out, how often and how they should be performed. All sterilization processes have process variables associated with them. The process variables are those which contribute to the attainment of sterilization by microbial inactivation. The purpose of validation, periodic and routine tests is to use monitoring systems which ensure that the process variables have been applied at sufficient levels to achieve microbial inactivation and therefore sterilization. For steam sterilization the process variables are temperature and time in the presence of moisture. Typically, in the UK, a saturated steam sterilization process will be carried out at 134 to 137 o C for an exposure time of 3-3.5 minutes in the presence of moisture supplied by saturated steam. Three basic methods are available for monitoring sterilization processes and a combination of one or more are used routinely. There are physical instrument methods designed to monitor one or more of the cycle variables e.g. pressure and temperature. There are biological indicators (BIs) which contain a resistant viable microorganism which is ultimately inactivated by an efficacious process.

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