June 17, 2022

Reprocessing of reusable medical devices is a critical step in ensuring patient safety. The Spaulding classification system assigns devices to one of three categories — critical, semicritical or noncritical — based on their risk of transmitting infection. The Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) use this system to determine the required level of device reprocessing.

Devices in the semicritical category, which includes flexible endoscopes, come in contact with intact mucous membranes or nonintact skin. The FDA requires devices in this category to undergo cleaning, followed by either steam sterilization or high-level disinfection (HLD) with a sterilant to eliminate pathogens.

A reported cluster of duodenoscope-associated carbapenem-resistant Escherichia coli infections, with no apparent lapses in endoscope reprocessing, has caused some to question the efficacy of HLD for some endoscopes. Since that initial report, concerns related to endoscope-associated transmission of infections has driven widespread interest in the use of low-temperature sterilization technologies, including ethylene oxide (ETO) gas sterilization, to reprocess these devices. ETO effectively destroys all residual microbes on appropriately cleaned instruments, but it requires long-time intervals for sterilization and aeration.

In an article published in Clinical Gastroenterology and Hepatology in 2022, Shounak Majumder, M.D., Michael J. Levy, M.D., and co-authors note that ETO gas sterilization, with or without performing HLD first, has become the favored method for endoscope reprocessing. Dr. Majumder, first author, and Dr. Levy, corresponding author, are gastroenterologists at Mayo Clinic's campus in Rochester, Minnesota.

"While ETO is effective in eradicating microbes, the impact of this process on endoscopic ultrasound (EUS) imaging equipment is unclear," explains Dr. Levy. "There is concern that this more intense form of processing may degrade the ultrasound transducer and the resulting EUS image quality, which is critical to providing an accurate diagnosis and to guide therapy. However, there are no published data assessing the potential harm of ETO sterilization to EUS imaging."

To address this issue, Mayo Clinic researchers conducted a study comparing EUS image quality in two groups of curvilinear echoendoscopes: devices reprocessed with HLD alone and devices reprocessed with both HLD and ETO sterilization.

"By collecting and analyzing this data, we aimed to test our hypothesis that reprocessing methods employing both HLD and ETO sterilization would degrade image quality as compared to using HLD alone in curvilinear echoendoscopes," explains Dr. Levy.

Study methods

Four new dedicated study devices were assigned to two groups. Group 1 included two devices reprocessed with HLD alone. Group 2 included two devices reprocessed with HLD and ETO. The devices were used for a median of 244 patients per endoscope over a two-year study period. The researchers performed a comprehensive assessment of still image and video quality obtained from all four devices at 12 time points: baseline, monthly for six months, and once every 3 to 4 months thereafter. Assessments at each time point included a blinded subjective review of still image quality and video performed by a panel of experts, and objective phantom-based image testing. Using linear mixed-effects models, the researchers then determined whether either device reprocessing method affected still image and video quality.

Results

According to Drs. Levy and Majumder, the study findings demonstrate minimal differences in still image and video quality between echoendoscopes reprocessed using HLD alone and devices reprocessed with HLD plus ETO.

• For clinical testing, mixed linear models showed minimal quantitative differences in linear analog scores over 24 months between the two reprocessing methods (P = 0.04; estimated change, 3.12; scale, 0 to 100).
• Although the overall image quality value data favored ETO reprocessing (P = 0.007; estimated change, -0.12; scale, 1 to 5), this change is minimal across the five-point scale and undetectable using the standard one-point assessment scale.
• Phantom testing revealed that the maximum depth of penetration was lower for echoendoscopes in the ETO group (P < 0.001; change in depth, 0.49 cm).

"Overall, these results support the use of ETO sterilization of EUS instruments if deemed clinically necessary," explains Dr. Levy.

Dr. Levy notes that additional research is needed to determine the infectious risk associated with EUS scopes and the long-term impact of ETO sterilization on EUS image quality.

"There is a need for more robust data to help clinicians understand the underlying risk of duodenoscope-associated infections and the true impact on patient care, especially given the current drive from industry to tackle this potential problem by employing nonreusable instruments. Additional data will be necessary to better determine the need and impact of such instruments," says Dr. Levy.

For more information

Majumder S, et al. Prospective study assessing impact of ethylene oxide sterilization on endoscopic ultrasound image quality. Clinical Gastroenterology and Hepatology. In press.

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