Standards and Methods for Using EtO

Medical Device & Diagnostic Industry Magazine
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An MD&DI  March 1998 Column

HELP DESK

James M. Gibson, a sterilization consultant with J. M. Gibson Associates (Odessa, FL), provides information about EtO sterilization with regard to clinical trials, personnel exposure, and humidity readings.

What is the industry standard for providing EtO-sterilized samples for clinical trials?

At this time there is no such industry standard. Many companies have developed internal procedures for sterilizing single clinical lots, which at least provide a written internal policy that recognizes a procedure.

If the product for clinical trials can logically be "adopted" into an existing product family because of similarities to a validated product, then that product's cycle can be used to expose the clinical trial lot. This adoption must be formally documented and supported by product-specific data including, at a minimum, bioburden, a half-cycle exposure challenged biologically with product sterility testing and biological indicators, followed by a full-cycle exposure for product release. EtO product residuals and functionality testing must be conducted and successfully passed before releasing the product for use in clinical trials.

The AAMI Industrial Ethylene Oxide Working Group has recognized the need for better guidelines in this area. The proposed TIR­16, Process Development and Performance Qualification for Ethylene Oxide Sterilization--Microbiological Aspects, contains a section titled "Small Batch or Lot Release," which addresses recommendations for clinical samples. The document is still in the draft stage but should be finalized later this year. Applying the guidelines presented in it is, therefore, premature, but the report may indicate a direction to take.

What methods can be used to measure the amount of EtO that operators are exposed to while unloading products from the sterilizer?

Personnel EtO badges and environmental monitoring systems such as gas chromatographs should be used to measure exposure to EtO during unloading. Because those personnel who unload the product may be exposed to some level of airborne EtO, they are typically required to wear self-contained breathing apparatuses and to follow recommended good handling practices, e.g., pulling rather than pushing the product. In addition, engineering controls are used to help limit exposure. These controls include rear chamber exhausts, i.e., exhaust systems at the opposite end of the chamber from the door that draw fresh air from behind the unloader to limit his or her exposure to EtO.

These precautions do not completely solve the problem because they do not address potential exposure during subsequent stages of handling, particularly entrance into aeration rooms. Using auto-mated loading and unloading systems can also help reduce personnel exposure concerns.

When should humidity be measured during the EtO sterilization process? We've heard that some manufacturers measure before, and others during, exposure.

ANSI/AAMI/ISO 11135, Medical Devices--Validation and Routine Control of Ethylene Oxide Sterilization, requires measurement of relative humidity in validation during preconditioning and conditioning but not during gas exposure. Two basic reasons exist for measuring humidity during these times. First, since relative humidity cannot be controlled when EtO is added, no scientific reason exists to measure this uncontrolled parameter. Second, and more important, the addition of EtO may affect the accuracy of humidity sensors' readout. Humidity sensors typically produce signals based on conductance change, a result of the absorption of moisture from the atmosphere around the sensor. Absorption of EtO can, theoretically, also produce a signal of some kind. In other words, strange humidity readings can occur when EtO is added. Whether these are true values has not been resolved.

There is also a potential safety issue with some sensors in 100% EtO cycles. Many sensors are not intrinsically safe. However, the new generation of self-contained, safe data loggers for temperature and humidity permits recording of data during the EtO exposure portion of the cycle.

"Help Desk" solicits questions about the design, manufacture, regulation, and sale of medical products and refers them to appropriate experts in the field. A list of topics previously covered can be found in our Help Desk Archives. Send questions to Help Desk, MD&DI, 11444 W. Olympic Blvd., Ste. 900, Los Angeles, CA 90064, fax 310/445-4299, e-mail [email protected]. You can also use our on-line query form.

Although every effort is made to ensure the accuracy of this column, neither the experts nor the editors can guarantee the accuracy of the solutions offered. They also cannot ensure that the proposed answers will work in every situation.

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