Autoclave sterilizers use steam heat to inactivate bacteria. Various cycle types accommodate various load configurations and materials.
An autoclave cycle must achieve sufficient temperature and time. Furthermore, air must be eliminated from both the chamber and the materials within. To be truly effective, an autoclave cycle must enact both of these steps simultaneously.
Steam Sterilization
Steam sterilization is an efficient means of disinfecting tools and equipment in hospitals, medical offices, and labs. The process utilizes pressurized and heated water (steam), which is then introduced to an autoclave chamber to disinfect its contents.
Steam’s high temperature can kill microorganisms while also denaturing them, rendering items safe for consumption and sterilizing them effectively. Therefore, its temperature needs to reach high enough levels for an efficient sterilization cycle—hence why the conditioning phase of sterilization cycles is vitally important. In this phase, the chamber and load are brought up to the recommended sterilization temperatures using Gravity Displacement or Dynamic Air Removal techniques.
Once conditions are in place, loads are sanitized by being exposed to steam for an established amount of time and temperature. To maximize sterilization efficiency, both should follow device manufacturer recommendations in terms of duration and temperature settings.
Autoclaves feature unique cycles designed to protect delicate glassware and sealed test tubes that would otherwise be damaged by rapid temperature changes and high pressure associated with traditional sterilization cycles. To guarantee their safety, these cycles may use lower temperatures, shorter cycle times, or even a combination of vacuum and steam-EtO sterilization techniques.
Most autoclaves feature a vacuum system that enables users to forcibly extract air from the chamber before and after every sterilization cycle. This helps ensure all condensates are boiled off and transported away and leaves the load dry when they exit. Moisture in the load could recontaminate itself with microorganisms exposed during sterilization; should this occur, validation procedures would need to be revalidated.
Vacuum Sterilization
Many laboratories and hospitals utilize Class B autoclaves, which are capable of sterilizing an assortment of instruments and materials that are too porous for steam to penetrate effectively, such as plastics, rubbers, and fiberglass. Furthermore, they come equipped with vacuum functions, which ensure steam penetrates even difficult loads effectively by eliminating air pockets within these items and creating uniform heating throughout the chamber.
After preconditioning is completed, a vacuum must be created in order to extract all air from both the load and chamber. Although this step takes longer than sterilization itself, it ensures complete sterilization of even difficult-to-steam items and prevents condensation within the chamber, which would lessen the effectiveness of the sterilization process.
Once all air has been removed from the chamber, the sterilizer drain closes, and high-temperature steam is continually introduced into it, gradually dislodging air within the load that then escapes through drain vents. For optimal results during this exposure period, pressure must remain steady to ensure all medical and laboratory items are effectively sterilized.
Once the exposure period is complete, temperature and pressure in the vessel are stabilized for a specific amount of time – known as the holding period – before being released back out again for sterilization. The length of this stage varies according to factors like load complexity, set temperature, and desired Sterility Assurance Level, during which biological and chemical indicators (BI/CIs) are tested to verify that the sterilization process has effectively killed bacteria, viruses and spores before terminating cycle and opening autoclave doors.
Gravity Displacement Sterilization
Autoclave sterilization cycles involve filling an autoclave’s pressure chamber with steam that is pressurized at a pre-set temperature and time, then pressurizing it further until reaching desired temperatures and pressures. As autoclaves constantly operate under high pressures, they require highly sturdy materials as well as various safety devices – including pressure gauges to signal when to open or close their door, whistle alarms to indicate when sterilization cycle completion has occurred, and an emergency fail-safe valve that opens steam lines to release pressure if electronic controls become disabled or disabled by software changes.
Sterilization cycles vary based on the size and type of load being sterilized, the sterilization temperature(s), and the Sterility Assurance Level (SAL) required. For instance, small lab autoclaves commonly used to sterilize glassware, unwrapped utensils, wastepaper baskets, red bags, and waste can typically run for 30 minutes at 270F; larger research-grade autoclaves that can handle more complex loads like animal cages or medical supplies may need much longer sterilization cycles at higher temperatures.
Class N or gravity autoclaves are the simplest autoclaves on the market, typically costing less and providing fewer features than vacuum models. Although more cost-effective, their limited versatility prevents all air from leaving their chamber and load chamber—generally limited to treating flat items such as medical waste and hard surfaces, as well as porous materials or instruments with internal channels, such as syringes.
Vacuum-powered Class B autoclaves employ a pump that produces a pre-vacuum to efficiently extract air from the sterilization chamber and load, enabling more thorough steam penetration into both areas. Therefore, they’re often the go-to choice for labs requiring sterilizing equipment of all kinds across multiple load categories.
