English
Among all sterilization methods, steam sterilization is the most commonly used method to kill microorganisms by using the heat released from high-temperature steam to coagulate and denature proteins. Steam sterilization has the advantages of being non-toxic to operators, having a fast sterilization speed, and being easy to control and monitor.
The basic principle of using autoclaves is to expose the items to be sterilized directly to steam at the specified time, temperature, and pressure. Therefore, the four key parameters of the steam sterilization process are steam, pressure, temperature, and time. Common steam sterilization temperatures are 121°C and 134°C. The sterilization time at a constant temperature varies depending on the type of item (e.g., metal, rubber, plastic, etc.), whether the item is wrapped or unwrapped, and the type of sterilizer.
The two basic types of autoclaves are the gravity displacement autoclave and the high-speed pre-vacuum sterilizer.
The gravity displacement autoclave, also known as a downward displacement autoclave, allows steam to enter from the top or side of the sterilization chamber. Since steam is lighter than air, it forces the air out through a vent at the bottom of the chamber. Gravity displacement autoclaves are primarily used for treating laboratory media, water, pharmaceuticals, regulated medical waste, and non-porous items that come into direct contact with steam. In gravity displacement sterilizers, penetration into porous items is prolonged due to incomplete air elimination.
The major difference between the high-speed pre-vacuum sterilizer and the gravity displacement type is that the high-speed pre-vacuum sterilizer is equipped with a vacuum pump to ensure that the air is completely removed before the steam enters the sterilization chamber. Pre-vacuum sterilizers are ideal for sterilizing porous items but cannot be used for autoclaving liquids since a vacuum is required. High-temperature pre-vacuum autoclaves have features such as short sterilization cycles, high efficiency, saving manpower and time, and thorough exclusion of cold air. However, the equipment and maintenance costs are higher, and the sealing requirements of the cabinet are more stringent.
As with other sterilization systems, the effectiveness of high-pressure steam sterilization is monitored by mechanical, chemical, and biological monitors. Steam sterilizers typically use graphical outputs to display temperature, time, pressure, etc., during the sterilization process. Additionally, chemical indicators can be used for monitoring, which change color or deform under certain temperature and conditions to indicate whether the required sterilization parameters have been met, such as commonly used pressure sterilization indicator tape. For biological monitoring, heat-resistant non-pathogenic bacterial spores are often used as indicator organisms to determine the effectiveness of heat sterilization.
