Ask the Editors
What are the basic differences among the variety of chemical indicators available for use in heat sterilization?
Chemical indicators use sensitive chemicals to assess physical conditions (e.g., time and temperature) during a sterilization process. Common forms are available as paper strips, labels, and steam pattern cards, which change color when certain temperature, time, and/or pressure conditions are reached during the heat cycle. Since they do not contain bacterial spores as the active agent, chemical indicators are not able to prove sterilization has been achieved. They are valuable, however, by being able to detect certain malfunctions and can also help to identify procedural errors. Autoclave tape is the historical example of a chemical indicator. It was used for many years as visible proof that items in the chamber had been exposed to a heat sterilization process. Unfortunately, the temperature-sensitive stripes on this tape appear long before sterilizing conditions are reached in the chamber; therefore, this external marker is the least sensitive indicator for heat sterilization.
Recommendations addressing sterilization monitoring continue to include chemical monitoring of cycles. In the comprehensive 2003 CDC guidelines, the recommendation is made: “Use mechanical, chemical and biological monitors according to the manufacturer’s instructions to ensure the effectiveness of the sterilization process.” Each load to be sterilized should be monitored with both mechanical and chemical indicators. In a possible event where heat and pressure conditions may not be the same inside and outside the pouch, the guidelines also call for using a chemical indicator on the inside of each package in order to verify that sterilizing vapor has penetrated to reach instruments. A relatively recent innovation has made it easier to accomplish this step. Instrument pouches are now available which contain built-in external and internal multi-parameter indicators. Those can provide valuable information to personnel regarding time, temperature, and sufficient exposure of processed instruments to steam.