A number of tools are available to assess the performance of the autoclave; these include physical, chemical and biological indicators. It is important to note that these indicators will only respond to time, temperature and moisture conditions, and not to organic load.

 

Physical Indicators:- Pressure and temperature recording devices such as thermocouples can be placed inside the load to determine the temperature achieved in the bag itself.

 

Chemical Indicators:- These indicators change colour after being exposed to specific temperatures, for example: heat sensitive tape. Upon exposure to the given temperature the change will occur; it is not time related. Therefore these indicators can only attest to the temperature attained and not to exposure time and hence success of sterilization.

 

Biological Indicators:- Biological indicators are used in the efficacy testing of the autoclave process to effectively sterilize the contents being treated. Bacillus stearothermophilus spores are used, as they are the most resistant organism to steam autoclaving. The standard for testing1 requires a 6 log10 reduction of spores to ensure a level 4 treatment. This means the spore ampule must contain a 106 population of spores, and those spores must be killed by the steam or heat treatment. Since spore vial populations come in more than one population density, it is important to purchase the correct test vials.

To determine the effectiveness of the autoclave process the biological indicator must be placed in a typical test load (solid or liquid) and exposed to the typical cycle conditions. This is the standard method of validating the effectiveness of autoclave procedures. Testing using a biological indicator must be undertaken at least every six days of operation or once every two weeks, whichever time is less. The testing regime should alternate between solid load verification and liquid load verification.

Solid Load Sterility Verification:

  1. Read and follow the supplier’s instructions.
  2. Place B. stearothermophilus in centre of representative test load.
  3. Process load in normal fashion
  4. Extract and incubate the ampule of B. stearothermophilus as instructed by the manufacturer.
  5. Use another ampoule (same lot #) not autoclaved to act as a positive control.
  6. Check for colour change at regular intervals during the incubation period (8, 12, 24, and 48 hours). If media is yellow and turbid the autoclave process has FAILED. Immediately upon noting yellow colouration, re-run all samples with new biological indicators.
  7. If failure continues to be noted, either increase the time of exposure or initiate repairs to the autoclave. Note the autoclave cannot be used again until validations procedure indicates that autoclave is now adequately sterilizing the material.
  8. Record all results. (Positive and Negative)

 

Liquid Load Sterility Verification:-

  1. Obtain a media bottle of the sizes that would normally be used for media.
  2. Tie a string to an ampule of B. stearothermophilus and then to a stir bar. Make sure the string length between the stir bar and ampule will allow the ampule to be suspended in the middle of the bottle contents.
  3. Fill the bottle with an appropriate volume of water and loosely cap the bottle.
  4. Place the bottle in the middle of a typical liquid load and process in the normal fashion.
  5. Extract and incubate the ampule as instructed by the manufacturer.
  6. Use a second unprocessed ampule from the same lot number to act as a positive control.
  7. Check for colour change at regular intervals during the incubation period (8, 12, 24, and 48 hours). If media is yellow and turbid the autoclave process has FAILED. Immediately upon noting yellow colouration, re-run all samples with new biological indicators.
  8. If failure continues to be noted, either increase the time of exposure or initiate repairs to the autoclave. Note the autoclave cannot be used again until validations procedure indicates that autoclave is now adequately sterilizing the material.
  9. Record all results (positive and negative).