Everything About Autoclaves
What is an autoclave?
An autoclave is a machine that uses steam under pressure to kill harmful bacteria and spores on items that are placed inside a pressure vessel. Autoclaves are also known as steam sterilizers. An autoclave can be used for healthcare or industrial applications. Three factors are critical in ensuring successful steam sterilization. They are time, temperature and moisture. The items are heated by the steam to an appropriate sterilization temperature for a given amount of time. The moisture in the steam efficiently transfers heat to the items to destroy the protein structure of the bacteria and spores.
Who invented the autoclave machine?
The steam digester, a prototype of the autoclave that is better known now as a pressure cooker, was invented by French-born physicist Denis Papin in 1679.1 In 1879, French microbiologist Charles Chamberland created a new version called the autoclave to be used in medical applications.
How does an autoclave work?
Autoclaves are commonly used in healthcare settings to sterilize medical instruments and supplies. The items to be sterilized are placed inside a pressure vessel. Air inhibits sterilization and must be removed from the vessel during the first phase of the sterilization cycle known as conditioning. In dynamic air removal-type steam sterilizers, the air can be removed from the vessel using a vacuum system. It can also be removed without a vacuum system using a series of steam flushes and pressure pulses. Gravity-type sterilizers use steam to displace the air in the vessel and force the air down the sterilizer drain. After the air is removed, the sterilizer drain closes and steam is continuously admitted into the vessel, rapidly increasing the pressure and temperature inside to a predetermined level. The cycle enters the exposure phase and items are held at the sterilization temperature for a fixed amount of time required to sterilize them. During the final phase of the cycle, exhaust, the sterilizer drain is opened and steam is removed, depressurizing the vessel and allowing the items in the load to dry.
Good quality steam is vital to a successful autoclave sterilization process. The steam used for sterilization should be composed of 97% steam (vapor) and 3% moisture (liquid water). This ratio is recommended for the most efficient heat transfer. When the steam moisture content is less than 3%, the steam is described as superheated (or dry). Superheated steam is too dry for efficient heat transfer and is ineffective for steam sterilization.2
What is the autoclave temperature range?
Commonly recommended temperatures for steam sterilization include 250° F (121° C), 270°F (132°C) and 275°F (135° C). To kill any microorganisms present, the items being sterilized must be exposed to these temperatures for the minimum time recommended by the manufacturer of the item. Exposure periods for steam sterilization vary with size, shape, weight, density and material composition of the item among other factors.3
What is autoclavable?
Medical devices that have contact with body tissues or fluids are considered critical items. These items may include surgical instruments, implanted medical devices and surgical drapes and linens. These items should be sterile when used because any microbial contamination could result in infection transmission. Autoclavable items must be stable under conditions of high heat and moisture and should be processed per the manufacturer's written instructions for use. Steam is often the sterilant of choice for sterilization of heat and moisture stable items because it is reliable, consistent, and lethal to microorganisms while being non-toxic to the operator of the autoclave.2
Industrial autoclaves vs. medical autoclaves
Autoclaves may be used in a variety of industrial and medical applications. Industrial autoclaves are used in manufacturing environments to process parts and materials using heated steam and pressure. Autoclaves are also used in the scientific research and pharmaceutical industries. Medical steam sterilizers are used in healthcare environments for the sterilization of heat and moisture-stable items such as surgical instruments, implanted medical devices and surgical drapes and linens. The cycles used in medical steam sterilizers are developed and validated according to recognized industry standards. In the United States, steam sterilizers used in healthcare must be cleared for use by the Food and Drug Administration for the sterilizer manufacturer's stated intended use.