EFHSS Questions and Answers - Question Q00439

How does an autoclave work?

Dear Mary,

This is a great question because so many people think of an autoclave as a "magic box" where you place items, push a button, and the items magically come out sterile!

A steam sterilizer (autoclave) uses steam as a carrier of thermal energy or heat. Steam is a much more efficient carrier of heat than air. The steam softens the outer layer of microorganisms which permits the thermal energy or heat to enter the organism and come in contact with the proteins in the organism. Heating the proteins causes changes in the nature of the proteins which is called denaturing, coagulation, or poaching of the proteins. Just as an egg white changes from a liquid to a solid when heated, the proteins inside the cells also change when heated. This change prevents critical proteins inside the cells from doing their jobs inside the cell to keep the cell alive.

Sterilization with steam depends on a properly elevated temperature, sufficient moisture, and sufficient time. Just as it takes time to cook food, it takes time to sterilize medical devices. In both cooking and sterilization, the higher the temperature, the faster the task is completed.

Most failures of steam sterilization are caused by a lack of contact by the steam with all surfaces to be sterilized. If a sterilizer load is packed too tightly or the individual packs are wrapped too tightly, the steam can not penetrate to the surfaces of the items to be sterilized. Any coating on the items to be sterilized, such as blood or oils, will protect the items from contact with the steam, resulting in the item not being properly sterilized. This is why proper cleaning of items before sterilization is so important. Closing ratcheted instruments such as hemostats or needle drivers will prevent steam from reaching surfaces where the metal is in contact with metal while subjected to pressure. Pans, bottles and any closeable containers must have their tops removed and loaded on the sterilizer cart on their sides so that the steam can reach all the surfaces. (When loading the sterilizer cart, imagine the containers are full of water and that you want the water to run out of the container.)

To learn more about how autoclaves work, I suggest that you read Josy Holdener's excellent answer to question Q00265.

Warm regards,
Pete Bobb

Mary

Just to add one point to Pete's response it is essential to remember that one extra requirement for the autoclave to perform correctly is the complete removal of air. Steam sterilizers exist in different forms which have different methods of removing air. A passive system will remove air from the chamber and surrounding solid unwrapped instruments. If the instruments are hollow or wrapped than an active air-removal system must be used. This will then require a means of automatically monitoring the success of this air removal in order to allow the sterilization cycle to continue. You should therefore select the proper autocalve for the type of load to be re-processed.

Best wishes - Peter Hooper