Guide to Steam Sterilization Cycles - Steam Flush Pressure Pulse
There are three types of steam sterilization cycles recognized by the Association for the Advancement of Medical Instrumentation (AAMI). They are gravity, prevacuum and steam flush pressure pulse (SFPP). These cycles differ in the way air is removed from the load during conditioning and may have different exposure times depending on the type of load being processed. Both Prevacuum and SFPP are classified as Dynamic Air Removal cycles by AAMI. All validated steam sterilization cycles provide efficacious sterilization when used according to manufacturer's instructions, but dynamic air removal cycles are preferred because they are more efficient than gravity cycles at removing air from the load.
Anatomy of a Steam Sterilization Cycle
Steam sterilization cycles can be divided into three distinct phases; conditioning, exposure and drying. During conditioning, air is removed from the load and the items in the load are heated to the desired temperature for sterilization. Conditioning is important because if there is any air in the load it may prevent the sterilant from coming into contact with load items, leading to sterilization failure. During exposure, the load is held at a specific temperature for a time known to provide effective sterilization. After exposure, steam is removed from the chamber and the load is dried to prevent recontamination of the instruments through wicking of microorganisms through a wet wrap.
During GRAVITY cycle conditioning, steam displaces the air in the chamber and the force of gravity causes the heavier air to exit the chamber via the sterilizer drain. Gravity cycles typically require more exposure time because the air removal method is more passive in nature.
PREVACUUM cycles condition wrapped loads through a series of pressurizations with steam and evacuations of the chamber using a mechanical vacuum system. The vacuum system facilitates more efficient air removal when compared to the gravity method, especially when processing lumened items. During evacuations of the chamber, the pressure in the chamber drops to below atmospheric. Consequently, if there are any leaks in the piping or sterilizer seal, the potential exists to re-introduce air into the chamber.
The Bowie-Dick test is conducted daily to ensure that the vacuum system is adequately removing air from the chamber and should be used in conjunction with a weekly leak test to determine if there are leaks in the sterilizer plumbing or seal.
The SFPP cycle was initially developed in 1988 and has been used for terminal steam sterilization since 1990 when it was cleared by the FDA for use in healthcare applications. The SFPP cycle conditions the load through a series of carefully controlled pressurizations and flushes with steam. No vacuum is drawn during conditioning and chamber pressures do not drop below atmospheric. Therefore, there is no need to conduct a daily Bowie-Dick test. Since the pressure in the chamber is greater than the ambient air pressure, reintroduction of air into the chamber through plumbing or seal leaks is eliminated, reducing the possibility of load recontamination.
Dynamic Air Removal - The Common Denominator in Prevacuum