Monitoring each sterilisation cycle

      1. Monitoring each sterilisation cycle

Monitoring each sterilisation cycle

Effective sterilisation of used instruments to prevent transmission of microorganisms depends on temperature, pressure and time – each of these parameters must be monitored.

The sterilisation cycle is monitored by multiple methods:

  • mechanical/physical/electronic indicators recorded by automatic printout or computerised data logger – must be checked for every cycle before the load contents are released for use
  • chemical indicators – included with every pack/pouch and load, and placed on each tray containing unwrapped items
  • biological/enzymatic indicators – used during validation and when steriliser operation needs to be rechecked.

All sterilisers must automatically generate log data (see Record keeping).

Mechanical/physical/electronic monitoring

Sterilisers must be fitted with devices (gauges/timers/digital readout) that provide visible evidence of the time, temperature and pressure during a cycle.

Results are automatically recorded by printout or a data log, which must be viewed after each cycle before sterilised items can be released for use. The printout or data logger shows the temperature and pressure at critical points during the sterilisation cycle as well as the drying time.

Chemical indicator monitoring

There are six classes of chemical indicator (classes 1–6). Higher classes provide more information (including more specific information) than lower classes (Table 10.10. Types of chemical indicators).

A Class 1 chemical indicator must be used on every pack of every load or in the tray of unwrapped items as evidence that the load has been subject to a heat process. Self-sealing pouches and some sealing tape incorporate Class 1 chemical indicators.

The use of other classes of chemical indicators is optional. For example, chemical indicators may be used to detect a suspected fault.

Chemical indicators must be checked for colour change immediately after unloading the steriliser, because the colour may fade or change over time. Colour viewed after storage does not provide proof of success of a sterilisation process performed days or hours before.

Any monitoring using chemical indicators must be recorded.

Table 10.10. Types of chemical indicators

Class Description When used Cycle type* Advantages Disadvantages
1 Process indicator (eg steriliser indicator tape) On every pack in every load
On the tray of every unpacked load
All classes Can assist in easily distinguishing between processed and unprocessed loads Designed to reach their endpoint after an exposure to a cycle that may be less than adequate for sterilisation
2 Specific test indicator (eg Bowie–Dick-type tests) According to practice risk assessment Class B Designed to show air removal and the rapid and even penetration of steam Designed to reach their endpoint after an exposure to a cycle that may be less than adequate for sterilisation
4 Indicator for two parameters (eg time and temperature) For extra assurance of successful completion of a sterilisation cycle
In the absence of printout/data log
All classes Designed to reach their endpoint after exposure to a sterilisation cycle at the stated values of the chosen parameter (eg 134°C for 3 minutes)
Provides more assurance of a successful sterilisation cycle than that provided by either process (Class 1) or single-parameter (Class 3) indicators and can be used in the absence of a printout
Failure may not identify which specific parameter/s have failed
5 Integrating indicators (eg time, temperature and pressure) For high-level assurance of successful sterilisation cycle
In the absence of a printout
All classes Provides as much information as a biological indicator by mimicking the conditions necessary to destroy microorganisms and can be used in the absence of a printout or validation in some situations Failure may not identify which specific parameter/s have failed
6 Emulating indicators (eg 134°C for 3.5 minutes in steam under pressure) Assurance that all critical conditions of the sterilisation cycle are met, based on the settings of the selected sterilisation cycles All classes Provides a very high level of assurance of a successful sterilisation cycle and can be used in the absence of a printout or validation in certain situations Failure may not identify which specific parameter/s have failed

*Steriliser type or cycle class of steam steriliser

Note Class 3 indicators (indicators for a single parameter) are no longer used.

Microbiological indicator monitoring

Microbiological indicators are the most reliable method for checking the effectiveness of the sterilisation process. They are not designed for routine monitoring or as a substitute for validation.

Types of biological indicators

There are two types of microbiological indicators: biological and enzymatic.

Biological indicators are designed to measure the killing power of the sterilising process and are considered to be the most accurate method. They consist of a predetermined number of microorganism spores.

Rapid-read biological indicators provide results in 20–25 minutes. Older biological indicator systems require 24 or 48 hours’ incubation after the sterilisation cycle before the result can be read.

Enzyme tests are similar to biological indicators but do not require an incubator. They contain an enzyme from a microorganism that is inactivated when sterilising conditions are achieved. The test is performed after the cycle by adding a drop of test solution and observing a rapid colour change. These are not commonly used in office-based practices.


The use of a biological indicator by the steriliser technician is required at operation qualification and performance qualification, recommissioning and performance requalification .

The use of biological indicators by the practice as part of routine testing and performance monitoring, and in criteria for release of processed items, is optional.1

A biological indicator can also be used as a quality assurance activity, to investigate cycle failures, or when running any load type that exceeds the previously validated worst-case parameters (in this case, the load must not be released for use until the results are available).


The biological indicator is placed on the tray with unwrapped items or within the sterile barrier systems of the load to be sterilised. After the cycle is complete, the indicator is incubated according to the manufacturer’s instructions. This can be done onsite in practices that own or have access to a loaned incubator. Incubators used for this purpose are annually calibrated.

Record the results in the steriliser logbook before releasing the load.1

Weekly use of biological indicators was formerly required when using sterilisers that were not calibrated and validated. Unvalidated or uncalibrated sterilisers must not be used.