How to Monitor Extended Steam Sterilization Cycles

Biological indicators (BIs) are critical tools used to monitor the lethality of a sterilization cycle. They do so by providing a challenge to the sterilization process as they contain highly resistant live spores that are killed at a given exposure time. Chemical indicators (CIs) also are used to confirm that certain sterilization parameters such as time, temperature, and exposure, are met.

But what happens when the steam sterilization parameters are changed with either a longer exposure or dry time – and how do Sterile Processing Departments (SPDs) reduce their risk when using extended cycles in autoclaves? Before reviewing this, it is important to understand the potential challenges with monitoring extended cycles.

What is an Extended Cycle for Steam Sterilization?

Extended cycles are specific to steam sterilization where the exposure of a standard sterilizer cycle (i.e. 270°F for 4 minutes) has been adjusted.

The Food and Drug Administration (FDA) defines extended cycles as “any sterilization cycle that includes specifications that deviate from those found on commonly used, FDA-cleared sterilizers, and for which there are limited or no FDA-cleared sterilization accessories. Extended cycles typically include longer exposure times and/or higher or intermediate temperatures, which may also deviate from more conventional sterilization cycles.”¹

Extended steam sterilization cycles pose a challenge for healthcare facilities because for example, with a biological indicator, if the cycle exposure time is extended, the spores will be killed before the additional exposure time has begun. Simply said, once a 4-minute BI is dead, it stops monitoring the sterilization cycle and therefore cannot be used to monitor a 10-minute cycle. Because of this, sterility assurance products not validated for specific extended cycles will provide no assurance of lethality for the additional exposure time.

How to Reduce Risks for Extended Steam Sterilization Cycles

Extended cycles pose a risk to Sterile Processing Departments if they are not using validated sterility assurance products for those cycles. So how can your department work to mitigate this risk? Your facility could choose to not use devices that have extended cycles in their Instructions for Use (IFUs) – but this is not a likely option. Instead, facilities need to develop appropriate policies and procedures, for monitoring extended cycles.

Due to the unique challenges of extended cycles, facilities must take care when developing policies and procedures for packaging and monitoring devices that require extended steam sterilization cycles. A BI that is labeled for a 4-minute, 270°F prevacuum cycle is designed to show passing conditions at the end of the 4-minute cycle. Since a 10-minute 270°F cycle requires 6 additional minutes, a challenge pack labeled for 4 minutes would not provide the additional challenge necessary to detect the failure of a 10-minute cycle.

While not all extended cycles have validated biological indicators or chemical indicators, there are some monitoring products validated for the more common extended cycles used by device manufacturers:

Table: A list of extended cycles with validated BI or CI products

Sterility Assurance Products Designed for Monitoring Extended Cycles

 VERIFY STEAM Integrating Indicator

The VERIFY STEAM Integrating Indicator is a Type 5 CI and validated for many extended Dynamic Air Removal Cycles such as 270°F 5, 6, 7, 8, 9 and 10 minute cycles.

Celerity™ Xtend 10 Assembly

The Celerity Xtend 10 Assembly is used with the VERIFY All-In-One STEAM Reusable Test Pack and is validated for routine biological monitoring of 270°F (132°C) dynamic air removal steam sterilization cycles with a 10-minute exposure time. 

Celerity™ 10 STEAM Chemical Indicator

The Celerity 10 STEAM Chemical Indicator (CI) is a Type 6 emulating indicator which requires all critical steam sterilization parameters (time, temperature and saturated steam) to be met. It is designed to specifically monitor 10 minutes 270°F (132°C) dynamic air removal steam sterilization cycles.

VERIFY^® SixCess^® Extended Timing Challenge Pack

The VERIFY SixCess Extended Timing Challenge Pack contains a Type 6 Emulating Indicator within a specially designed barrier system. This cycle specific test may be used to monitor steam sterilization cycles operating at 270°F (132°C) with exposure times of 4, 10, or 20 minutes.

Related STERIS University Courses:

¹ U. S. Department of Health and Human Services Food and Drug Administration. (2017). Reprocessing Medical Devices in Health Care Settings: Validation Methods and Labeling - Guidance for Industry and Food and Drug Administration Staff. Retrieved from http://www.fda.gov/downloads/medicaldevices / deviceregulationandguidance/guidancedocuments/ucm253010.pdf