Complex Medical Devices and Steam Sterilization

By Andrew Gay Director - Sterilizer Validation Australia

About 10 years ago, during a routine Performance Qualification test, an observation was made that changed the way in which I now approach PQ testing. During the test, long thermal penetration times were measured within the lumen of a yankauer sucker like the one pictured here.

At first it was thought that there was some interference or fault with the test equipment, however, repeated tests to similar instruments, within dozens of different sterilizers revealed a consistency common to the design and construction of some instruments and their resistance to thermal penetration.

The light blue and pink traces in this chart indicate the typical temperature curve of Yankauer suckers within a typical pre-vacuum sterilizer. Note this is a 134

C 4 min sterilize phase.

Advancement in surgical techniques and new complex instrumentation pose even grater challenges to thermal penetration times, the likes of the yankauer

sucker.

The red and pink traces in this chart indicate the typical temperature curves for some complex surgical instruments such as those indicated in the previous slide. Note this is a 134

C 11 min sterilize phase.

This instrument set looks simple enough?

Take a closer look at what the manufacturer has stamped on the handle of the cannulated

screw driver.

134

C 18 min sterilize phase?

Can that be correct?

Testing to the cannulated screw driver reveals that in this test this instrument does not even reach 134

C within an 18 minute sterilize phase! However, repeated tests reveal that the core temperature within the lumen handle reaches and maintains ≥121

C for 15min or more, achieving an acceptable SAL. In some cases lethality mapping is used to calculate and prove SAL.

This is the complete cycle chart for the test in the previous slide.

1.3.37 Penetration time (equilibration time) The time required for every part of a load to reach

the selected sterilizing temperature after that temperature has been reached in the sterilizing chamber

1.3.43 Processing time The total time of the sterilizing stage after the load

in the sterilizing chamber has reached sterilizing conditions (penetration time plus holding time including safety factor).

Extract from AS/NZS 4187:2003, Section 1.3 DEFINITIONS

“Table 4.1 is used as the recognized international temperature pressure-time relationship for steam-under-pressure sterilization. “ “Using Table 4.1, penetration times shall be established and added to the holding time, including safety factor. All time and temperatures are based on the assumption that the items to be sterilized are thoroughly clean.” “NOTES: 1 The processing time of a steam sterilizer equals penetration time plus holding time (which includes safety factor).”

Extract from AS/NZS 4187:2003, section 4.2, page 36

New Standards There is a new ISO standard which has been drafted and is now in the final stages of editing before release. The document proposed - ISO17665 part 3 – “Sterilization of healthcare products – Moist heat - Guidance on the designation of a medical device to a product family and processing category for steam sterilization” will assist users in applying methods to identify and group instrument into a product family for reprocessing. The document includes a methodology to assist users in identifying possible “difficult to sterilize” medical devices and states that in certain cases where a sterilizer does not have a process that delivers the required SAL due to factors such as insufficient thermal penetration time, the medical devices would form a separate special Product Family, for which

“sterilization process should be developed and qualified” It should be noted that much of the data and research considered for this new document in regards to the testing of complex medical devices, was provided from Australia.

Will changes to AS/NZS 4187 change the requirements in relation to penetration

times and holding times? While AS/NZS 4187:2003, (Cleaning, disinfecting and sterilizing

reusable medical and surgical instruments and equipment, and maintenance of associated environments in health care facilities) is currently in the latter stages of review and editing before release for public comment, the current standard addresses what should be done in the case of devices with long thermal penetration times. The standard states: Penetration time shall be established and added to the holding time And The processing time of a steam sterilizer equals penetration time plus

holding time

Performance Qualification - what de we need to do? Establish and test the worst case scenario for each

identified “product Family” ensuring the test establishes the efficacy, reliability and repeatability of the process as defined by the applicable standards.

This includes establishing thermal penetration times for the most challenging products, in the most challenging configuration.

Product Family = Complex Parameters:

•Pre-vacuum air removal •Sterilize Phase – 134degC for 3.5 minutes •Drying time 30min

Instruments with Thermal Penetration times of ≤30sec ≤

PQ Example – Complex Product Family From the available instruments at a facility this cannulated screw diver is identified for inclusion. Experience indicates this instrument will have a thermal penetration time of between 3 and 8min at 134

C A thermocouple is inserted in the instrument at the estimated cold spot and packed for testing.

PQ Example – Complex Product Family

The test reveals a thermal penetration time of approximately 6min 10sec

PQ Example – Complex Product Family Penetration time measured within the device = 6m 10sec* *Worst Case of three consecutive tests at 134°c sterilization temperature.

Minimum holding time as per AS/NZS 4187 2003 = 3min at 134°c

Sterilization Processing Time = Penetration time + minimum Holding Time

The Sterilization Processing Time for this product and like products having an equal or lesser thermal penetration

time should be 9m 10sec. For practicalities this would be round up to 10min at 134°c

Product Family = Complex Parameters:

•Pre-vacuum air removal •Sterilize Phase – 134degC for 10 minutes •Drying time 30min

Instruments with Thermal Penetration times of ≥30sec and ≤7min.

Product Family = Complex Special Parameters:

•Pre-vacuum air removal •Sterilize Phase – 134degC for 18 minutes •Drying time 20min

Instruments with Thermal Penetration times of ≥10min@ 134degC

Product Family = Low Temperature Parameters:

•Pre-vacuum air removal •Sterilize Phase – 121degC for 30 minutes •Drying time 25min

Instruments with Thermal Penetration times of ≤15min@ 121degC

FAQ Do all products need to be sterilized for 10min at 134°c? Answer - No, typically most products have thermal penetration times of

30sec or less, so a standard process with a sterilization processing time of 3min 30sec to 4min at 134°c is sufficient.

Note: always refer to the manufactures instruction in regards to product limitations and recommended reprocessing instructions.

How do I know which products require a longer sterilization time? Answer – During PQ our technician will work with your staff in learning

to identify potential “complex products” by their construction, materials, configuration, mass and design. We also attach a list of products we may have tested before that know to have longer than 30 sec penetration times. We also offer 12 months phone support after PQ to assist in this process