Episode #310 Moisture Matters In Anesthesia Circuits

Opening Clip: [Feldman] “The clinical impact of moisture in the circuit depends upon both anesthesia machine design and clinical practices. Reducing fresh gas flow consistent with a low-flow anesthesia practice will increase the amount of moisture in the circuit, but it can be done safely with attention to moisture mitigation. Clinicians are advised to understand the best practices for moisture mitigation based upon their own practice and the specific devices that they use.”

[Bechtel] Hello and welcome back to the Anesthesia Patient Safety Podcast. I’m your host, Alli Bechtel. Last week, we reviewed the investigation into mold and moisture in the GE operating room ventilators. The team discovered that most anesthesia professionals were unaware of the concerns for moisture accumulation in the anesthesia circuits or simple mitigations sets such as removing the breathing circuit or flow sensor overnight or using a condenser. Another important finding was that higher levels of moisture accumulation were found in anesthesia workstations with higher case volumes and longer surgical durations. Following the investigation, there were some practice changes to help address mold and moisture accumulation that included extensive education, regular machine assessments, regular removal of the breathing circuit and flow sensor overnight with add on condenser elements for all GE HealthCare OR anesthesia workstations, annual sterilization of all OR ventilators, and collaboration with GE HealthCare.

Our conversation ended with several questions from the investigative team to the APSF and GE HealthCare. We have some answers for you today!

Before we dive further into the episode today, we’d like to recognize PPM, Preferred Physicians Medical Risk Retention Group, a major corporate supporter of APSF. PPM has generously provided unrestricted support to further our vision that “no one shall be harmed by anesthesia care”. Thank you, PPM – we wouldn’t be able to do all that we do without you!”

Our featured article is “Moisture, Mold, and More in GE Operating Room Ventilators: System Response and Mitigation” by Sandeep Narayan and Katie Passaretti. This is a Rapid Response Article that was published online February 1, 2026. To follow along with us, head over to APSF.org and click on the Newsletter Heading. The third one down is Rapid Response to Questions from our readers. Then, you can scroll down until you get to our featured article, and I will include a link in the show notes as well.

Now, let’s set to the Q&A. A big thank you to Jeff Feldman for providing some of the answers here for the podcast. Please check out the show notes for additional links and information.

QUESTION 1: Please educate on the need for multiple filter use for each patient—is it necessary to have both HME filters and expiratory filters for all patients? If a site decides to use just one filter, which filter is the preferred filter for adult and pediatric populations?

[Jeffrey Feldman 1] “ The short answer is that APSF recommends that a pleated filter be placed between the expiratory limb and the anesthesia machine. A high-quality filter in that location should prevent respiratory pathogens from entering the anesthesia machine. It is not uncommon to place another pleated filter between the machine and the inspiratory limb as a safety against pathogens from the machine getting to the patient. But there is little evidence to suggest that this is a significant patient safety concern. Heat and moisture exchange devices placed at the airway often include filters that are effective against bacterial and viral pathogens, although they are not as effective as the pleated filters. The sampling tube for side stream gas analysis can also bring pathogens into the machine, which can be prevented by attaching the sampling tube to an HME filter at the airway. Many side stream devices that are internal to the anesthesia machines are configured with filters to protect the machine, although you should check with the manufacturer to confirm. APSF has two resources that were published during the COVID-19 pandemic that are germane to this discussion. The links are provided in the newsletter article.

QUESTION 2: Please educate on the need for moisture mitigation when using non-GE HealthCare ventilator brands.

[Jeffrey Feldman 2] “ The authors are correct to observe that anesthesia machines from different manufacturers vary in the approach to moisture mitigation. Water traps and heating elements in the breathing circuit are commonly used. There are too many anesthesia machines in use to provide a detailed explanation for every machine. Manufacturers are a reliable source of information on how to approach moisture mitigation in a specific machine. The clinical impact of moisture in the circuit depends upon both anesthesia machine design and clinical practices. Reducing fresh gas flow consistent with a low-flow anesthesia practice will increase the amount of moisture in the circuit, but it can be done safely with attention to moisture mitigation. Clinicians are advised to understand the best practices for moisture mitigation based upon their own practice and the specific devices that they use.”

QUESTION 3:

Is there any evidence or guidance on moisture levels that are safe within ventilators and breathing circuits?

[Jeffrey Feldman 3] “ I am not aware of specific moisture levels that are considered safe. Moisture is desirable in the breathing circuit if it prevents drying of secretions and the respiratory mucosa, but it becomes unsafe when moisture interferes with sensor measurements or results in the growth of pathogens. Heat and moisture exchange filters are a useful barrier for keeping the lungs moist and reducing the amount of moisture entering the machine. They will not, however, reduce the moisture created by carbon dioxide absorption, which increases when using a low-flow practice.”

QUESTION 4:

Please provide guidance on OR ventilator sterilization frequency. Should this be a part of yearly preventative maintenance?

[Jeffrey Feldman 4] “ After discussing this question with colleagues from the ECRI Institute and anesthesia machine manufacturers, we could not identify a rationale for recommending a specific interval for OR ventilator sterilization. While the manufacturers provide specific guidance to sterilize the breathing circuits, it is a time-consuming process which introduces cost and complexity. In reality, the anesthesia breathing circuit is never a sterile component and is always exposed to organisms and contaminants in the environment. Reasonable indications for sterilization would include visible internal contamination of the circuit or perhaps after caring for a patient with a pathogen known to be transmitted through the respiratory system, for example, tuberculosis.”

Thanks again to Jeff for contributing to the show today and helping to provide some answers from the APSF. Now, let’s check out the response from GE Healthcare by Robert Myers and John Beard. They have reviewed the report from Advocate Health and acknowledge that moisture accumulation in a known characteristic of all modern anesthesia rebreathing systems from patient exhalation and the chemical reaction of CO2 absorption. These 2 factors are not unique to GE Healthcare systems. Moisture management and reprocessing is important to prevent microbial growth especially in warm environments and the GE anesthesia machines have features and recommended equipment maintenance instructions to help manage moisture accumulation.

There are several design and moisture management features to support low-flow anesthesia and to work in environments with 100% humidity. Optional components to manage moisture accumulation include condensers to collect and drain excess moisture and heat and moisture exchange or HME filters to reduce moisture from entering the breathing circuit. The newest models of GE Healthcare anesthesia machines include a condenser within the CO2 absorbent canister so the add-on condenser is not needed.

For maintenance, disconnection of the breathing circuit and air drying the breathing system are helpful strategies. There is no fixed reprocessing frequency, but institutions should follow local infection prevention policies and clinical usage patterns. Using inspiratory and expiratory bacterial and viral filters are recommended to reduce contamination. For cleaning and sterilization, GE offers guidance in the User Reference Manuals as well as training resources.

GE HealthCare agrees with the investigators that the patient safety risk is minimal especially with the use of bacterial and viral filters. GE supports continued vigilance and routine inspection of workstations especially in settings that utilize low-flow anesthesia and longer duration anaesthetics.

GE HealthCare is working on optimizing customer support to ensure the most effective use of their equipment. Part of this involves the expansion of their educational outreach to emphasize moisture mitigation strategies combined with technology, like End-Tidal Control, that supports low-flow anesthesia practice.

GE assures us that moisture accumulation is not expected to impact ventilator performance, but in the sensing lines, it could affect flow sensor performance and tidal volume measurement. This is why there are cross-checks and alarms such as “calibrate, dry, or replace flow sensors” to alert users to potential issues. Keep in mind that airway pressure measurements remain unaffected due to the location of the measurement port and the flow sensors are located in an elevated position to stay dry in the gas pathway.

Here is the response to the specific questions. First up, information about option condensers:

“GE HealthCare offers condensers as optional accessories for Aisys CS² and Avance CS² models. As moisture accumulation is dependent on clinical practice, the condenser is not required by all customers—it is offered as an optional accessory if additional moisture management is needed.”

And here is the response about education initiatives:

“GE HealthCare is continually enhancing its training programs and documentation to ensure consistent understanding of moisture mitigation strategies across all customer sites.

Inspiratory/Expiratory Filters and Moisture: These filters are primarily designed to prevent microbial contamination, not to manage moisture. HME filters are more effective for moisture control.”

And finally, here is the conclusion that I’m going to read now.

“GE HealthCare is grateful to participate in this discussion of moisture accumulation in anaesthetic breathing systems. We value the collaboration with Advocate Health and APSF to identify and address issues proactively while expanding knowledge to the medical community. We encourage all users to consult our URMs and reach out to our support teams for guidance on best practices for moisture management and workstation maintenance.”

Thank you so much to Robert and John and GE Healthcare for contributing to this Rapid Response. We hope that this information will help you in your practice to manage moisture and prevent mold growth in the anesthesia workstations especially with the use of low-flow anesthesia practice. And don’t forget to check out Figures 3 and 4 in the article for an example educational flyer and moisture and mold check list.

If you have any questions or comments from today’s show, please email us at [email protected]. Please keep in mind that the information in this show is provided for informational purposes only and does not constitute medical or legal advice. We hope that you will visit APSF.org for detailed information and check out the show notes for links to all the topics we discussed today.

As we wrap up this episode of the Anesthesia Patient Safety Podcast, we’d love to hear from you. If you’ve encountered a technology-related safety concern in your practice, consider submitting a Rapid Response article to the APSF Newsletter. The goal of the Rapid Response column is to encourage timely communication about emerging safety issues, while also providing input and perspective from manufacturers and industry representatives. Submissions should be limited to 1,000 words and up to 15 references. Your experience could help improve patient safety for anesthesia professionals around the world.

Thank you for listening to the Anesthesia Patient Safety Podcast. If you enjoyed this episode, please subscribe, share it with your colleagues, and help us continue the conversation about safer care for every patient, every time.

Until next time, stay vigilant and stay informed so that no one shall be harmed by anesthesia care.

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