Chinese Standard GB18279:2000 is equivalent to ISO 11135:1994. I understand that Chinese authorities will be reviewing this standard in the coming year in order to align it with ISO 11135:2007.

PVC likely will show severe discolouring at the doses that you mention, both immediately after irradiation and after accelerated aging. Also, PVC has a tendency to crosslink. This will slightly stiffen the tube. If these phenomena do occur and are unacceptable to you, you could try to find a radiation-stabilised grade of PVC.

General information about a material’s compatibility with a sterilisation process can be found in AAMI TIR17:2008. Please note, however, that ISO 11137-1:2006 requires the setting of a maximum acceptable product dose. This means that a formal test programme, including product irradiations and subsequent real-time ageing, should be set up to determine the highest absorbed dose at which the product will continue to meet all of its specifications (functional and biocompatibility) during its defined shelf life.

ISO 10993-7 was published in October 2008 and has a three-year transition period, so the 1995 version will be withdrawn officially in 2011. However, any revalidation projects or assessment of ethylene oxide levels for new or existing products should be performed in accordance with the 2008 version of the standard.

In my opinion, it is important to begin assessments to ISO 10993-7:2008 as soon as possible because it may be necessary to redesign or optimise the sterilisation cycle to meet the more stringent requirements contained in the latest version of the standard.

Ethylene oxide sterilisation is not recommended for medical devices that contain any form of stored energy (i.e., electrical, chemical, pressurised gas) because this energy may be a potential source of ignition.

In extreme cases, however, where no other method is available to sterilise medical devices that contain batteries, EtO has been used. In my view, to achieve the absolute minimum safety requirements for such procedures, make sure that the following steps have been taken:

1.    A full review of design of device has been performed by senior Safety Management executives, including a review of subcomponent circuit diagrams to assess energy storage and discharge characteristics

2.    Several layers of safety have been designed into the device to prevent accidental discharge when it is in the sterilisation chamber

3.    The sterilisation cycle has been designed to be significantly below the flammability curve for ethylene oxide

4.    Effective change control procedures have been put in place for the product design and sterilisation cycles to prevent change unless authorised by the relevant safety specialists.

Medical devices containing batteries should not be sterilised by EtO methods unless these criteria have been met and all rationale and decisions have been properly recorded.

To achieve the minimum aeration quarantine time necessary to meet  ISO 10993/7, there are two possible options.

 Validation of a new cycle: Minimising the impact and cost of a new cycle design is important, so creating an optimised version of an existing cycle can be beneficial in that it means that any product and packaging functionality data may continue to be valid. If this approach is used, the key process parameter that should be optimised is EtO gas dwell time. In order to reduce this to the minimum necessary to achieve the required product sterility assurance level (SAL), a change of validation method may bring significant benefits. If the product SAL has been established using the so-called half-cycle approach (ISO 11135-1:2007 Annex B.1.2 a), which is regarded as an overkill method, a reduction in gas dwell time is best achieved by changing to the methods described in Annex A. These methods quantify the deactivation rates and allow a more targeted SAL to be selected, which will in turn permit a shorter gas dwell to be used in routine sterilisation. This reduction in gas dwell time is likely to reduce product residue levels and therefore permit the use of shorter aeration times. It is a good idea to perform an initial qualification experiment to quantify potential benefits before embarking on a full requalification exercise.

Use of dynamic aeration: Traditionally, products sterilised by EtO are quarantined in aeration at a controlled temperature for a defined time until the product residue levels comply with the limits specified in ISO 10993/7. Dynamic aeration is a more efficient way of outgassing products and can bring significant reduction in the traditional aeration time. It is best performed in the sterilisation chamber and involves the use of combinations of vacuum levels and holds and air/other gas washes that are selected based on product design and the materials used. This method will increase the residence time in the sterilisation chamber; the associated costs must be balanced against the reduction in traditional aeration time.

It is a good idea to gather experimental data to verify that the BI provides a greater challenge than the natural product bioburden. This is achieved first by characterising the product bioburden in accordance with ISO 11737-1 using a validated method. Products are then selected that have representative bioburden and are packaged as normal. These products are placed alongside process-challenge devices that contain BIs. Both types of products are subjected to a validation cycle that is designed to be sublethal for the BI but lethal for the product bioburden. (Note: Historical validation data should be reviewed to determine the gas dwell exposure time necessary to achieve this outcome.) After exposure to the validation cycle, the BIs are subjected to an endpoint sterility test by direct inoculation, and the product bioburden samples are sterility tested in accordance with ISO 11737-2. If a fraction or all of the BIs test positive, and the product bioburden sterility tests are negative, this demonstrates the appropriateness of the BI relative to the natural product bioburden. It is then necessary to ensure the product bioburden is controlled and monitored in accordance with ISO 11737-1.

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