Physical/Mechanical indicators monitoring the sterilization process

July 22, 2018

Introduction

Sterilization is an essential stage which is used in the processing of any product.
These products are destined for parenteral administration, or for contact with broken skin, mucosal surfaces, or internal organs where the threat of infection exists.
The sterilization of microbiological materials, soiled dressings and other contaminated items is necessary to minimize the various health hazards associated with these articles.
The sterilization processes involve the use of a biocidal agent or physical microbial removal process to a product or preparation.
These processes target the killing or removing of all microorganisms.
There are various physical indicators that are used in the monitoring of the sterilization process.
They are as follows:

1. Heat sterilization processes

A temperature record chart is made of each sterilization cycle with both dry and moist heat (i.e. autoclave) sterilizers in this process.
This chart forms part of the batch documentation and is compared against a master temperature record (MTR).
The temperature should be taken at the coolest part of the sterilizer which is recommended.
The thermocouples are used that are placed at selected sites in the chamber which might be inserted directly into test packs or bottles.
This also provides further information on heat distribution and penetration within sterilizer.

2. Gaseous sterilization

Temperature probes are used to monitor the elevated temperature for each sterilization cycle.
Routine leak tests are also performed to ensure gas tight seals.
Records of pressure and humidity measurements are kept.
Gas concentration is measured independently of pressure rise, often by reference to weight of gas used.

3. Radiation sterilization

The use of a plastic (often Perspex) dosimeter is recommended which gradually darkens in proportion to the radiation absorbed.
This gives an accurate measure of the radiation dose and is considered to be one of the best techniques currently available in radio-sterilization process.

Image source: slideshare

4. Sterilizing filters

These filters are subjected to a bubble point pressure test which helps in determining the pore size of filters.
These are also used to check the integrity of certain types of filter device (membrane and sintered glass) immediately after use.
The principle of this test is that the wetted filter is subjected to an increasing air or nitrogen gas pressure differential in its assembled unit.
The pressure difference which is recorded when the first bubble of gas breaks away from the filter is the maximum pore size of the filter used.
When the gas pressure is increased further slowly, there is a general eruption of bubbles over the entire surface.
The pressure difference recorded now is related to the mean size of the pore.
A pressure differential which is below the expected value would signify a damaged or faulty filter.
Measuring the diffusion of gas through a wetted filter at pressures below the bubble point pressure is also a modified test for membrane filters.
A faster diffusion rate than expected would again indicate a loss of filter integrity.
A filter is considered ineffective when an unusually rapid rate of filtration occurs.

Image source: slideplayer

4. HEPA filters

These filters are used to supply sterile air to aseptic workplaces.
Its efficiency is tested by the generation of upstream of dioctylphthalate (DOP) or sodium chloride particles of known dimension followed by detection in downstream filtered air.
Retention efficiency is recorded as the percentage of particles removed under defined test conditions.
Microbiological tests are not normally performed.

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