Episode #231 Ensuring Anesthesia Safety: Risks of CO2 Canister Replacement and Technology Concerns

Hello and welcome back to the Anesthesia Patient Safety Podcast. My name is Alli Bechtel, and I am your host. Thank you for joining us for another show. We are bringing you a Rapid Response to Questions from our Readers show today! That’s right. Fasten your seat belts and keep your hands and arms inside the vehicle because we are turning up the speed on our journey to improve anesthesia patient safety.

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

We are continuing to discuss the amazing articles from the October 2024 APSF Newsletter. Today, we are reviewing the Rapid Response to Questions from our Readers Column and the article, “Replacing CO2 Absorbent During Surgery – The Risk of Hypoventilation Continues” by Yuki Kuruma. To follow along with us, head over to APSF.org and click on the Newsletter heading. The first one down is the current Newsletter. Then, scroll down until you get to our featured article today. I will include a link in the show notes as well.

We are so excited to have exclusive content from the author to help kick off the show today. Here she is now.

[Kuruma] “Hello,  my name is Yuki Kuruma and I am just an ordinary anaesthetist at Saiseikai Matsusaka General Hospital, Japan.”

[Bechtel] I asked Ka-room-ma why she feels so passionate about this topic. Let’s take a listen to what she had to say.

[Kuruma] “Ten years ago, it was shocking to me that intraoperative canister replacement that , in hindsight, was not necessarily required was putting a healthy young patient at risk for hypoventilation with the brand-new anaesthesia workstation.  Even if you do not have detailed knowledge about anaesthesia machines, you can use them intuitively. However, problems with anaesthesia machines have the potential to harm any patient undergoing general anaesthesia. With the climate crisis and increased awareness of cost reduction, intraoperative absorbent replacement has become a more necessary practice than ever before.

I wrote this article to once again raise awareness about the risk of ventilation failure due to absorbent replacement, and to inform all anaesthesia machine users about early detection of abnormalities, prevention, and what to do if ventilation failure occurs.”

[Bechtel] Thank you so much to Kuruma for writing this article and contributing to the show today. Without further ado, it’s time to get into the article. Dear Rapid Response. Back in 2013, the authors reported on a case of hypoventilation due to a massive leak from a defective Dragersorb disposable absorbent canister which was replaced during the surgery using the Fabius GS premium anaesthesia workstation. This can be found in the Letters to the Editor section of the Winter 2013 APSF Newsletter. I will include a link to that article in the show notes as well.   Over 10 years have passed since the authors highlighted this threat to anaesthesia patient safety and there continue to be similar cases being reported on other Drager anaesthesia machines including the PerseusA400 and the Primus without any specific actions to address this threat of hypoventilation after replacing a CO2 absorber during surgery. Keep in mind that this risk is present in other non-Drager anaesthesia machines as well, but the actual implications of a defective canister will be different depending on the anaesthesia machine design. The authors call for action is for a Warning label to be added to the instructions for use for all anaesthesia machines that allow for changing the absorbent canister when in use during a procedure so that anaesthesia professionals are aware of this risk and can take steps to keep patients safe.

Let’s take a look at a clinical scenario. Imagine that the Fabius GS machines arrive in your department and for the first time, you can change the absorbent canister during the procedure. This allows you to really use all of the absorbent so there are some cost-saving benefits and less waste. The case from the 2013 APSF Newsletter article describes an uneventful mid-surgery change of the canister without any initial problems. That all changed at the end of the procedure, when after changing to manual ventilation. At that time, the breathing bag completely collapsed and could not be re-inflated despite maximum fresh gas flow and repeatedly pressing the oxygen flush valve. Has this ever happened to you during a case? The next step was for the anaesthesia professionals to disconnect the patient’s endotracheal tube from the anaesthesia machine and continue ventilation with a Jackson-Rees circuit and an external oxygen tank. Once the patient was breathing spontaneously and appropriate for extubation, this was accomplished without any further difficulty. Afterwards, a large hole in the absorbent canister was discovered which caused the massive leak and inability to create pressure in the circuit. Keep in mind that the unique design of the Fabius machine is a fresh gas decoupling valve which is what made mechanical ventilation possible, but manual ventilation impossible in the face of a large leak from the absorbent canister.

Check out Figure 1 in the article. It is a great visual depiction of this type of leak can impact ventilation. This is a schematic of the Drager Piston-type Breathing Circuit. The design of this anaesthesia machine use a fresh gas decoupling valve in the breathing system which prevents fresh gas from entering the circuit during inspiration and is located between the piston-type ventilator and the fresh gas inlet. The CO2 absorber is located between the fresh gas inlet and the breathing bag. There is a CLIC adaptor that allows the absorbent canister to be replaced when the machine is in use. The fresh gas decoupling valve allows inspiratory pressure to be maintained during mechanical ventilation even if there is a big leak in the canister that is attached to the CLIC adaptor. During expiration, as the piston retracts, ambient air can be entrained from the defect in the absorber into the anaesthesia circuit. You may notice changes in gas concentrations in the circuit due to the entrained air but the speed and degree of the change depends on the size of the leak so it may not be noticed immediately and would not be expected to trigger any alarms initially. Everything changes when you switch to manual ventilation mode because the ability to deliver positive pressure by the reservoir bag would be compromised by the canister defect and result leak leading to a collapsed reservoir bag and inability to provide manual ventilation.

Now, if we turn our attention to Figure 2, we can see the schematic for a turbine-type ventilator, such as the Drager Perseus and Zeus. This anesthesia machine does not have a fresh gas decoupling valve. Instead, the breathing bag fills with fresh gas and functions as a reservoir for the ventilator. During mechanical ventilation, inspired gas comes from the fresh gas flow and the reservoir bag. A leak in the absorbent canister would lead to changes in the gas concentrations since ambient air would be entrained from the leak into the circuit. Tidal volumes would remain the same. Once again, the changes in gas concentration due to the leak depends on the size of the leak as well as the total fresh gas flows that are set. This breathing circuit has unidirectional flow meaning that fresh gas will continue to fill the reservoir bag during mechanical ventilation. When the switch to manual ventilation is made, the leak will make manual ventilation difficult or impossible.

If you don’t have Drager anesthesia machines then you might be thinking that this is not something that you need to worry about, but other manufacturers have developed anesthesia machines with the ability to change the absorbent while the machine is in use. These include GE Healthcare, Mindray, and Getinge. The impact of a defective canister depends on the machine design. There is a 2015 case report in the Canadian Journal of Anesthesia that describes a leak in a GE anesthesia machine after replacing the disposable canister leading to inability to provide mechanical or manual ventilation. This brings us to another type of ventilator design, the ascending bellows ventilator that can be found in the GE Healthcare and Mindray anesthesia machines which also do not have fresh gas decoupling valves. Check out Figure 3 for a visual depiction of the circuit. During mechanical ventilation, the reservoir bag is excluded from the circuit and if there is a leak in the canister, this will cause the bellows to collapse during inspiration leading to a failure of mechanical ventilation. Manual ventilation will also be difficult even though the bellows are left out of the circuit since the reservoir bag will not fill due to the leak. Changes in the bellows or reservoir volume depends on the size of the leak. It is important to consider that if there is a new leak and the canister was recently changed, then that may be the first place to look for a leak.

We have one more type of anesthesia machine to discuss. This is the volume reflector which can be found in the Getinge anesthesia machines and the Mindray A9. There are no published reports of canister leaks impacting the volume reflector ventilators, but let’s take a look at the schematic that can be found in Figure 4 in the article to evaluate the system design. First stop, the ventilator and breathing bag are located upstream of the absorber. During mechanical ventilation, the reservoir bag is excluded from the circuit and during manual ventilation, the ventilator is excluded from the circuit. The volume reflector provides a continuous supply of 100% oxygen as the drive gas. The drive gas pushes gas to the patient, but does not enter the patient circuit. If there is a defective canister and a new leak, the drive gas may provide some ventilation to the patient depending on the size of the leak and this will lead to diluted anesthetic gas in the circuit and altered oxygen concentration. Once again, manual ventilation may not be possible due to reservoir bag collapse.

We have more to talk about when it comes to defective canisters, ventilator leaks and difficulty with ventilation. We will be back next week to continue to our discussion. Plus, we are going to discuss the response from Jeffrey Feldman, who is the chair of the APSF Committee on Technology as well as several members of the Drager team.

Kuruma includes an important warning at the end of the article. There is a risk of impossible manual ventilation following replacement of a CLIC disposable CO2 absorbent canister during a procedure if the canister has an undetected leak. Remember, for anesthesia machines with a fresh gas decoupling valve, mechanical ventilation may still be possible. An important step is visual inspection of the cannister to look for any defects. This is followed by careful monitoring of tidal volume, inspiratory pressure and gas concentrations after an intraprocedural canister replacement. Make sure that you have a manual resuscitation device, auxiliary oxygen supply, and intravenous anesthetics immediately available to prevent patient injury in the event of an anesthesia machine failure.

Before we wrap up for today, we are going to hear from Kuruma again. I also asked her what she hopes to see going forward. Here is her response.

[Kuruma] “Dräger and GE Healthcare’s responses revealed that it is possible to detect canister leaks early during surgery. As a clinician, I want to prevent canister leaks before providing patient care.

I hope that some kind of device or method will be developed to detect canister leaks.

I also hope that this article will be translated into multiple languages, read by many people, and help make anaesthesia safer. Thank you.”

[Bechtel] We are so excited to have had the chance to share this article and message on the podcast. It is important to identify these threats to anaesthesia patient safety, evaluate and troubleshoot, and then share this knowledge to help improve anaesthesia patient safety.

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.

Did you know that the Rapid Response column is designed to allow quick communication of technology-related safety concerns raised by our readers, with input and response from manufacturers and industry representatives? Do you have a tech-related anesthesia safety concern? Submissions should be less than 1000 words with no more than 15 references. Feel free to submit at any time, but deadlines for each issue are as follows: November 1^st for the February issue, March 1^st for the June issue, and July 1^st for the October issue. We would love to hear from you so go ahead and start working on your submission now!

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

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