Before making comments on the test, it is important to remember the one and only accepted definition on the international standard ISO 11140-1 for chemical integrating indicators type 5, which says: “An integrating indicator shall be designed to react to all critical process variables. The SVs1 are generated to be equivalent to, or exceed, the performance requirements given in the ISO 11138 series for BIs. The minimum SV shall be related to the minimum values required to achieve sterilization as specified in International Standards ISO 11135, ISO 11137 (all parts), ISO 17665 (all parts), or by local regulatory agencies”. This means, for steam sterilization, that the chemical integrating indicator must integrate all temperatures over time and reach the final point when the desired F0 value2 has been met. The standard ISO 11140-1 also says that the minimum SV for the integrating indicators is 16,5 minutes at 121 ºC, which would be the equivalent to an F0 value of 16,5 minutes.
- chemical indicators
- steam sterilization
- ISO 11140
The same standard is also mentioning that the indicators should be tested with special equipment called resistometers, and those should be constructed in accordance to ISO 18472. Thus, its important to point out that it is not correct to test indicators in other equipment than resistometers, and therefore they should not be tested in hospital sterilizers. Despite of this, some users test the indicators without following the instructions written on the standards, to which the following comments can be made:
Testing integrating indicators by aborting the sterilizer cycle before reaching the plateau
As it has been explained already, and according to international standards, the integrating indicators are designed to reach the final point when the desired F0 value has been met. Therefore, in a standard steam sterilization cycle with fractionated air removal, the F0 value considers the sum of all the values where the indicator has been exposed to temperatures over 100 ºC. This means that the following are the steps where in most cases the temperature- time integral (F0 value) is met and thus the inactivation of microorganisms is also reached (at least on the point of measurement):
- All the times during conditioning phase (pre vacuum steps) where the temperature is over 100 ºC.
- Heating up time when the temperature is between 100 ºC and the temperature at which the cycle is cancelled (typically 134 ºC)
- Pressure reducing time to remove steam from the chamber while the temperature stays over 100 ºC.
Citation: Pilasi Pendás M. Building a culture of quality at the centre of our service. Steri-World 2019; 2 (Feb)
- ISO 11140-1: Sterilization of health care products – Chemical indicators – Part 1: General requirements (ISO 11140- 1:2014)
- ISO 18472: Sterilization of health care products – Biological and chemical indicators – Test equipment
- ISO 17665-1: Sterilization of health care products – Moist heat – Part 1: Requirements for the development, validation and routine control of a sterilization process for medical devices
- ISO 11138 parts 1 and 3: Sterilization of health care products – Biological indicators Part 1: General requirements Part 3: Biological indicators for moist heat sterilization processes