Why Doesn't Depyrogenation Occur in Autoclaves?

Why Doesn't Depyrogenation Occur in Autoclaves?
Authored By Medical Equipment Services Admin

Are you looking for the best form of sterilisation for your dental or medical clinic? Autoclaves are the ultimate in medical equipment sterilisation as they don't allow depyrogenation to occur. Read below for more details.

Pyrogens are toxins that are excreted or expelled by bacteria. 

These pyrogens (known as endotoxins and exotoxins) are more difficult to destroy and often remain behind after the bacteria have been eliminated in a variety of different sterilisation processes. 

The process of destroying or deactivating pyrogens is referred to as depyrogenation and includes the following methods:

  • Ion Exchange Chromatography
  • Ultrafiltration
  • Distillation
  • Reverse Osmosis
  • Dilution and/Or Rinsing
  • Adsorption
  • Dry Heat
  • Moist Heat
  • Chemical Sterilisation
  • Gaseous Sterilisation
  • Ionising Radiation
  • Soft Hydrothermal Processing

The various methods are used in different applications and to achieve depyrogenation of different types of materials or elements. 

For example, reverse osmosis and ultrafiltration are commonly used to sterilise water or other liquids whereas the other methods can be used to destroy pyrogens on solid materials.

In order to achieve depyrongenation through the application of heat, pyrogens need to be exposed to high temperatures for an extended period of time. Temperatures of 250 degrees Celsius for a period of 30 minutes has shown proven results in testing to effectively eliminate or deactivate pyrogens. 

However, dry heat application is far more effective than moist heat application. 

So why does depyrogenation not occur in autoclave equipment? There are 3 main reasons why total depyrogenation cannot be achieved in autoclaves:

  1. Moist Heat

Both boiling and autoclaving is not considered to achieve depyrogenation due to the use of moist heat. 

Moisture helps prevent the destruction or deactivation of pyrogens. 

Although an autoclave uses steam rather than water to achieve the temperatures necessary to destroy bacteria, microorganisms, and other pathogens, the process does involve some moisture and will therefore not achieve total depyrogenation. 

Items that carry pyrogens are therefore not entirely sterilised in an autoclave. 

However, autoclaves are still considered to provide better sterilisation of medical instruments, equipment, and other items than most other sterilisation methods.

  1. Temperature

Autoclaves generally reach a temperature of 121 degrees Celsius in order to achieve sterilisation. 

However, this is far below the recommended 250 degrees Celsius for the destruction of pyrogens. 

While the maximum temperature of the autoclave is ideal for destroying other pathogens, depyrogenation cannot be achieved at these temperatures. 

Endotoxins are especially resistant to heat and extreme temperatures are necessary to eliminate or deactivate this pyrogen.

  1. Time

Autoclave cycles vary depending on the type of material that needs to be sterilised and the volume of items placed in the autoclave. 

Commonly, where fragile items or items that are susceptible to high temperatures for extended periods of time are placed in the autoclave, sterilisation time may fall below the recommended time of 30 minutes to achieve depyrogenation. 

The recommended autoclave time to destroy bacteria and other pathogens are however also 30 minutes and it is generally not advisable to run an autoclave for a shorter period of time in order to achieve complete sterilisation. 

Taken into consideration with the fact that an autoclave does not achieve the required heat to achieve depyrogenation, extending the period of time in an autoclave will also not be more effective at destroying or deactivating endotoxins or exotoxins.

The lack of depyrogenation does however not mean that autoclaves do not provide effective sterilisation. 

Tests rely on the fact that pyrogens exist in the first place in order for depyrogenation to be necessary. 

Pyrogens should not be present on items that are sterilised regularly and consistently in an autoclave. 

Immediate and consistent destruction of bacteria will eliminate these pyrogens from existing in the first place. 

However, this is not a scientifically proven fact and it is important to keep in mind that depyrogenation does not occur in an autoclave when using it for sterilisation purposes.

If you are searching for the best autoclave supplier in Australia, then look no further than Medical Equipment Services Australia

We were originally established in 1952 in order to provide electro-medical products to healthcare professionals across the country. 

The company (Medical Equipment Services) was acquired by Medical Equipment Australia in 2009. Since then, we have also expanded into the dental industry. 

For all your medical and dental supply requirements, please call us today on 1300 432 013 or contact us here.


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