ETO Validation

ETO sterilization validation is the documented procedure for obtaining, recording and interpreting the results required to establish that the sterilization process will consistently yield a product complying with predetermined specifications (ANSI/AAMI/ISO 11135-1). Validation of the ETO sterilization process yields a documented procedure of consistently confirming the inactivation of all living microorganisms, confirmation that the product or device is sterile, and confirmation that the process is repeatable.

NASP offers a full range of validation services and will assist customers to whatever degree is necessary. We can make recommendations, write protocols, run the validations and write the reports. Documentation of all validations remain at NASP permanently.

Validating a cycle for routine use is a time consuming process. When performing the validation of a sterilization process you must perform an Installation Qualification, an Operational Qualification and a Performance Qualification.

An installation qualification (IQ) is the process of obtaining and documenting evidence that equipment has been provided and installed in accordance with its specification.

An operational qualification (OQ) is the process of obtaining and documenting evidence that installed equipment operates within predetermined limits when used in accordance with its operational procedures.

Performance qualification (PQ) is the process of obtaining and documenting evidence that the equipment, as installed and operated in accordance with operational procedures, consistently performs in accordance with predetermined criteria and thereby yields product meeting its specification. (ANSI/AAMI/ISO 11135-1)


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Basically with an IQ we demonstrate that we have installed the sterilization equipment and any ancillary items in accordance with their supplier specification, with an OQ we demonstrate that the installed equipment is operational according to its intended use, with a PQ we demonstrate using product, that the installed equipment is operates consistently and performs according to your intended use producing product that is sterile.
With most industrial sterilizers, the IQ and OQ are typically already done unless there is a change to any equipment. Rather, commissioning, which is the verification that the equipment is operating as required, is performed on an annual basis. The PQ however is the part of the process that must be performed to qualify a new product, a new cycle, or introduce a change to products, packaging, etc unless adoption or equivalence to an already validated product can be demonstrated. Once the performance qualification is completed, the process may be run routinely.

AAMI/ANSI/ISO 11135-1 Sterilization of healthcare products – Ethylene Oxide –Part 1: Requirements for development, validation and routine control of a sterilization process for medical devices is the standard that must be followed for validating a sterilization process. The most common method of performing the performance qualification is to follow the half cycle “overkill” method. This is demonstrated by performing one sub-lethal cycle, three half cycles, and three full cycles. The purpose of the half cycle “overkill” method is to demonstrate a 6 log spore reduction at half the time of the proposed routine cycle, therefore stating that at the proposed routine exposure, the biological indicator will be reduced to a 12 log spore reduction.


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The biological indicator (BI), often referred to as the process challenge device (PCD) is the test system which contains viable microorganisms given a defined resistance to specific sterilization processes. For EO sterilization the biological indicator most commonly used is a 106 spore of Bacillus Atrophaeus, which is the most resistant microorganism known to EO sterilization. When these microorganisms are exposed to enough ethylene oxide they are killed. When you expose a 106 BI to the half time sterilization cycle and it tests negative it has now been reduced by a 6 log spore reduction to 100. Because microorganism death is logarithmic this will confirm a 12 log spore reduction at the routine time.
The science behind this is that when you spore a load with BIs that are 106 or 1,000,000 microorganisms, expose it to a sterilization process, and test it at the lab; if the BI’s are all negative you have reduced the microorganisms from 106 to 100 at a minimum. This method therefore demonstrates that at twice the half time, or the proposed routine time, you will then reduce the BI by another 6 log spore reduction down to 10-6.

All of this is verified during the performance qualification which consists of 2 main steps, the physical qualification and the microbiological qualification. The physical qualification requires three consecutive runs to demonstrate the reproducibility of the process and that the acceptance criteria are met throughout the load for the durations of the proposed routine process. It confirms that the process is operating within the required parameters and the load is reacting properly. This is confirmed by reading the load sheets which are produced by the sterilization equipment and by using sensors. The loads must contain the proper amount of temperature sensors and humidity sensors. The required amount is based on the volume of the product load.


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The microbiological PQ shall demonstrate that when exposed to the sterilization process the requirements for sterility are met. The load shall be representative of the most challenging to sterilize routine load. This is demonstrated using the biological testing previously described. This is confirmed using biological indicators. The required amount is based on the volume of the product load. In addition to the biological indicators, several other microbiological testing is required. The validation process is broken up into three loads. The first load consists of a sub-lethal cycle, half cycle and full cycle. The second and third loads consists of each a half cycle and full cycle.

For each load of three separate lots bioburden testing must be performed. Bioburden is the natural level of microorganisms that are on a product or device. This testing ensures that the product bioburden is consistent and does not contain more microorganisms that the intended PCD. This is done pre-sterilization. Bacteriostasis and fungistasis must be performed following sterilization for one load to confirm that the product has no bacteriostatic or fungistatic properties which might interfere with the test results. Product sterility testing must be performed following each of the sub-lethal and half cycles to confirm the sterility assurance level has been met.


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There are two types of BI/PCDs used, internal and external. Internal PCDs are placed in the hardest to sterilize positions of the device and external PCDs are placed externally to the load and will be used to monitor routine processes. When performing a sub-lethal cycle you are looking for partial positives and partial negatives. What this means is that you want the product sterility and internal BI/PCDs to be all negative but want the external BI/PCDs biological indicators to have a mix of positive and negative. This confirms that the product is less resistant to the sterilization process than the PCD.

With a half cycle you want everything to be negative, both products and internal and external PCDs. This demonstrates the 6 log spore reduction. The full cycle is more representative of the routine load therefore it has limited microbiological testing. The full cycles require external PCDs which must all be negative, and samples for residue testing. Ethylene oxide sterilization often leaves EO residua and ethylene chlorohydrin residues. Samples must be tested to detect the levels of patient exposure. All samples must be compliant with the most recent version of ANSI/AAMI/ISO 10993-7 entitled, Biological Evaluation of Medical Devices – Part 7: Ethylene Oxide Sterilization Residuals.

After the microbiological and physical PQs have been completed a report is generated to present all of the data. The process is then considered qualified and may begin to be used for routine sterilization. Although the cycle has been qualified, it is recommended by AAMI that a requalification be performed annual and consist of at a minimum a documented review of all applicable processes to verify that nothing has changed that would affect the process. It is recommended that a revalidation study using a minimum of a 1 half-exposure cycle run at minimum conditions be performed at least every two years. In case of significant changes, the appropriateness of the revalidation time and criteria will be evaluated.