The Principles of Medical Device Decontamination

Physical processes can be subdivided into those which take place at a high temperature (e.g. 121 to 138 o C) and those at a low temperature (room temperature to 80 o C). Processes achieving microbial inactivation using a micro-biocidal chemical usually employ oxidising agents such as hydrogen peroxide or alkylating agents such as Ethylene Oxide (EO). These processes almost invariably take place at lower temperatures and are often described as low temperature sterilization (LTS). In a healthcare setting the majority (ca 90%) of reusable sterile medical devices will be sterilized at high temperatures and pressures in moist heat sterilization processes employing saturated steam. The majority (ca 90%) of single use medical devices produced by the medical device industry will be sterilized in a LTS process, commonly irradiation with ionising radiation (e.g. gamma) or using EO gas sterilization. However, the industry is actively investigating alternative low temperature processes such as those employing vaporised hydrogen peroxide (VH 2 O 2 ) as an alternative to EO. There are many International and European standards (implemented as British Standards) and locally produced guidance for both sterilization processes and sterilizers. In the UK each of the four home nations will have produced its own guidance, broadly similar, as Health Technical Memoranda (01-01). Table 10.1 lists International and European standards implemented as British Standards for sterilization processes and sterilizers.

Sterilization Processes

There are certain variables associated with a given sterilization process which are needed to achieve microbial inactivation. These are termed the process variables. There are other variables which are used to control and monitor sterilization processes, and these are termed cycle variables. The following sections identifies each for each process.

Physical Methods - High Temperature - Moist Heat Sterilization process

Moist Heat or steam sterilization is carried out using saturated steam which comes into direct contact with the surfaces that need to be sterilized. This creates a moist heat environment which at the right temperature and for sufficient time, rapidly inactivates microorganisms.

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