Sterilization control indicators

The color change of these chemical substances indicates compliance with the basic parameters of the sterilization process, namely the time and temperature of sterilization.

To control the critical indicators of this process, more complex indicators are used. The following parameters are considered critical:

• In the case of steam sterilization – temperature, duration of its exposure, saturation of water vapor;
• With the air method – temperature and duration of its exposure;
• In gas sterilization methods – temperature and duration of exposure, concentration of the gas used, relative humidity;
• With radiation sterilization – the value of the total absorbed radiation dose.

Since the beginning of 2002, the state standard GOST R ISO 11140-1 "Sterilization of medical products. Chemical indicators. General requirements" has been in effect in our country. This regulatory act governs the division of all chemical indicators into six classes.

The first class includes indicators that serve as "witnesses" of processes, for example – thermal indicator tape, which is used to wrap sterilization boxes or textile packages before the start of the process. The changing color of the tape indicates that the package or box has been sterilized. These indicators are also used to monitor the sterilization of surgical linen and surgical instruments.

Second-class indicators are used in conducting special tests, such as the Bowie-Dick test. This type of test is not intended to control sterilization parameters, but to assess the removal of air from the steam sterilization chamber.

Third-class indicators allow the evaluation of only one parameter, for example – assessing temperature without obtaining data on the duration of its exposure.

The fourth class includes indicators with multiple parameters. Such substances contain dyes whose color changes under the combined effect of several sterilization process indicators at once, which in most cases are temperature and its duration. An example is thermal time indicators used in monitoring sterilization by the air method.

The fifth class includes integrating indicators that respond to any of the critical indicators of the sterilization process. The characteristics of indicators of this class can be compared to the inactivation of highly resistant microorganisms.

The sixth class includes emulator indicators, whose reaction manifests when the critical parameters of the sterilization process reach any control values.

In addition to chemical and physical methods, sterilization can be controlled by bacteriological means, based on the fact that during the sterilization process, a certain number of test microorganisms resistant to the sterilizing agent are placed.

Disposable chemical indicators for steam sterilization are produced in the form of rectangular strips, the base of which is made of film and paper. On one side of such indicators, markings and two color marks are applied, one of which is an indicator and the other is a reference standard. The red-orange indicator mark irreversibly changes its color as the critical parameters reach certain values during the steam sterilization process.

The reference standard has a dark blue-violet shade, which the indicator mark should take after all critical indicator values have been met. The reverse side of such an indicator is coated with a layer of adhesive substance, covered with a protective film. Indicator products are supplied in sheets, where the indicators are separated from each other by perforation.

Disposable chemical indicators for the steam sterilization process SteriTEST-P-120/45-02 and SteriTEST-P-132/20-02 are manufactured in accordance with TU 9398-042-11764404-2003. The purpose of the product is visual control of compliance during the steam sterilization process of such critical indicators as temperature, holding time, and the presence of saturated water vapor. Indicators can be used inside sterilized items or special sterilization packages. Steam sterilization using such indicators is carried out in steam devices, where steam purging ensures the removal of air from the sterilization chamber.

In addition, indicators are used to monitor the effectiveness of the air removal process from the sterilization chambers of steam gravity sterilizers included in the Test-IX. Such control is carried out in accordance with the current instruction "Control of air removal in sterilization chambers of steam sterilizers with a gravity pumping method," approved by the State Sanitary and Epidemiological Supervision of the Ministry of Health of the Russian Federation on December 18, 2003, No. 11-7/18-09. According to the classification of GOST R ISO 11140-1, the described indicators belong to the fourth class, that is, to indicators with multiple parameters.

Indicators, both before and after use, do not have a negative impact on the environment, so they can be stored under normal conditions and do not require any special disposal.

It is recommended to use indicators during each sterilization cycle. The placement of indicators should be performed by medical personnel during the preparation of items for sterilization, or in clinical departments without a central sterilization department (CSD). In sterilization departments, indicators may be placed by personnel packaging the items to be sterilized. To achieve optimal results, indicators are placed in hard-to-sterilize points of the items:

• In items such as clothing, sheets, and gauze, i.e., those with a uniform porous load, the indicator is placed in the middle;
• In items with cavities, such as flasks or gloves, the indicator is placed inside the cavity;
• In the case of items made from vapor-impermeable materials, such as oilcloth or polymer films, indicators are placed between layers or folds;
• In the case of individual packages with items that are difficult to sterilize, more than one indicator may be used.

The biological indicator is supplied as an inoculated carrier in primary packaging, ready for use. Such indicators have a certain resistance to sterilization under the specified mode.