Daily 'Hollow ARSPT' vs 'Porous ARSPT'?
Complete air removal is particularly difficult with porous loads such as linen and with hollow items such as cannulated instruments, dental handpieces or re-usable aspirator tips. However, without complete air removal, the item will not be sterile. Since the killing effectiveness of steam sterilisation results from the transfer of the latent heat of condensation that occurs when the steam comes into direct contact with a micro-organism, it is imperative the steam directly contacts all surfaces of the item being sterilised. Physical debris such as blood, body fluids or body tissues will act to insulate the surface of the item from direct contact with the steam as will any air trapped within the steriliser chamber or instrument.
The purpose of ARSPT or air removal and steam penetration tests (so named in AS5369:2023) is to prove that your steriliser continues to be capable of removing all of the air from both the chamber and all parts of the load including from within porous or hollow items so that steam can effectively penetrate all parts of the load. The tests are designed to simulate air removal from a full load and must therefore be processed in an empty chamber.
Air removal and steam penetration tests are available in two types, based on the type of load to be sterilised. The manufacturer of the test will indicate which type of test it is either on the packaging or on the accompanying documentation.
The first type of tests are commonly known as Porous ARSPT or Bowie-Dick tests, named after the doctors who originally developed the ‘chemical indicator wrapped in towels’ version of this test. These tests are specific for porous loads such as fabric. You would use this type of test to confirm air removal and steam penetration if your loads include medical drapes or other linen. Various formats of this test are available from different manufacturers, most based on the principle of removing air through the equivalent of thick fabric layers, allowing steam to penetrate to the centre of the load. Most of these tests are single use.
The second type of tests are Hollow ARSPT (previously known as a Helix Device). These tests are more rigorous than the porous test as they are designed to demonstrate that the steriliser can effectively remove the air from a Narrow Lumen/Hollow A device as defined in AS5369:2023. These tests normally incorporate a long, fine calibrated tube of specific internal diameter and specific length to provide the equivalent of a Narrow Lumen/Hollow A device. Most of these tests are a re-usable device with single use indicator that is fitted into one end of the device.
Note: Other types of tests similar in appearance to the Hollow ARSPT tests are available and care should be taken to ensure they are not mistakenly used for this testing. One type, usually matched to particular brands of sterilisers, are calibrated to show that the steriliser continues to meet the performance specifications set down by the steriliser manufacturer. These may not necessarily be designed to show air removal and steam penetration equivalent to Narrow Lumen/Hollow A. The other PCD’s are batch control devices designed to be processed in each cycle with a normal load. These are for load monitoring purposes only and are not necessarily designed for the testing described here. However, there are some tests, like the STS Professional HART Test which can be used for both daily and routine testing.
Both the ARSPT tests include a Type 2 indicator strip within the test that requires exposure to steam and time at temperature to achieve a colour change.
For small steam sterilisers (<60L) AS5369:2023 states that you must refer to the steriliser manufacturer's instructions for use for guidance on which ARSPT to use for the load. For example:
- Hollow ARSPT for load with hollow instruments or
- Porous ARSPT for load with porous instruments.
Daily testing of your steriliser using the appropriate test will provide you with the assurance that the vacuum system on your steriliser is functioning correctly to allow proper sterilisation of your loads throughout the day.
Please note that this information is general in nature and is based on the Australian Standards listed above and should only be taken as a guide and not advice. Please refer to product manufacturers instructions for detailed use.