STERILIZER

Typical Number in Hospital: 20

Cost Bands: 1,3,4

References: 2

Sterilization of instruments and equipment may be effected by several methods according to the durability of the item and the degree of sterilization required. Methods include the following:

1. Dry heat. Some items may be sterilized by heating to 150[d]C or more in a special oven. The items are normally wrapped in special paper sealed with tape which includes a colour indicator to show when the process has been completed. Some care is required to ensure that items made of different materials are not damaged due to the differential expansion rates of the components.

2. Pasteurization. Delicate items (e.g. some plastic items) may be sterilized by heating in water to 70-75[d]C for a minimum of 20 minutes. Most infective agents are destroyed but the process is only really suitable where a high degree of sterilization is not required.

3. Boiling. Boiling for a least 10 minutes is a satisfactory method for most metal items. Tubing and instruments with complex contours may not be adequately sterilized.

4. Autoclaving. This is probably the most satisfactory and widely used method. Instruments are packed in special paper sealed with an indicator tape to show completion of the process, and are placed in a pressure vessel which first exhausts the air before releasing high-pressure (and therefore high-temperature) steam into the chamber. Because of the vacuum created initially, the steam penetrates to every part of the equipment. After a few minutes (depending on the steam temperature used) the steam is evacuated leaving the instruments dry. Many plastic items and some rubbers are damaged by repeated autoclaving.

5. Chemical sterilization. Fumigation or immersion in anti- bacterial agents may be appropriate for some items. However this cannot provide reliable sterilization with complex items, or tubing unless great care is taken. An exception is ethylene oxide sterilization which employs a process similar to the autoclaving cycle to ensure total penetration of all contours. Such machines are complex and expensive to purchase and operate, and require meticulous anti-pollution measures since the gas is highly toxic.

6. Gamma rays. Many disposable items are sterilized by irradiation from a gamma-ray source. This is highly effective but disrupts the polymer structure of some plastics causing hardening, decomposition and discolouring.