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Low and Minimal-Flow Anesthesia Delivery with the Drger Perseus A500

Recently MedWrench spoke with David Karchner, MBA, Senior Director of Marketing, Operation Room Solutions at Drger, about low- and minimal-flow anesthesia delivery with the Drger Perseus A500 anesthesia machine.

Tue Dec 01 2020By Dräger

Dräger shares benefits, tips, and common issues regarding low-flow and minimal flow anesthesia. Have a question for the expert or want to find out more after reading his tips? Fill out the form at the bottom of the page to ask David Karchner a question directly.

In general, what is low- and minimal-flow anesthesia delivery? 

Low- and minimal-flow anesthesia delivery are methods of fresh gas delivery on continuous gas flow anesthesia machines. In some instances, anesthesia machines are run with fresh gas flows of 2 liters per minute up to greater than 6 liters per minute. Reducing this flow to 1 liter per minute is referred to as low-flow; a further reduction to .5 liters per minute is called minimal-flow. Running anesthesia machines at lower flows offers a number of financial, clinical, and ecological benefits. 

What are the benefits of this technique of fresh gas delivery?

Hospitals can experience financial, clinical, and ecological benefits from using the Dräger Perseus A500, a continuous gas flow anesthesia machine that is optimized for low- and minimal-flow anesthesia delivery. General anesthesia using low- and minimal-flow techniques helps reduce the consumption of costly volatile anesthetic agents, which can save hospitals a substantial amount of money each year and can help hospitals improve their ecological footprint. Further, low- and minimal-flow anesthesia helps protect the patient’s lungs by supporting the humidification and warming of the gas with which the patient is being ventilated. 

How does the Perseus A500 specifically help hospitals achieve the benefits of low- and minimal-flow anesthesia delivery?

That’s a great question. First, to help standardize the practice across all users, the Perseus A500 offers the easy to use Low Flow Wizard efficiency feedback tool. The on-screen tool provides simple traffic light-type feedback to help users lower their fresh gas flow by taking certain variables into consideration such as set fresh gas flow, patient uptake, and leakages and providing feedback in an easily understood format. The ability of the Low Flow Wizard to help customers reduce agent consumption was validated by a peer-reviewed study published in the journal Anesthesia & Analgesia which showed a median percent reduction in volatile liquid anesthetic consumption rate of 53.2%. 

Of course, during low- and minimal-flow anesthesia delivery, less fresh gas enters the breathing system so it’s important to prevent any unnecessary losses of gas volume. One easy way to do this is to recirculate gas continuously sampled for analysis back into the breathing system for continued ventilation. In doing so, you’re preserving gas volume helping you get down to truly low- and minimal-flows and you’re also able to save potentially significant anesthetic agent costs since that sampled gas can also contain anesthetic agent. For example, a hospital with 10 anesthesia machines sampling gas at 200 ml/min, agent usage mix of 70% Sev and 30% Des (Sev bottle: $96, Des bottle: $126), with 4 cases per day, per OR, 90 minutes per case, and expected device lifetime of 12 years would prevent approx. $167,000 worth of agent from being wasted to the atmosphere. To put the ecological benefit into perspective for this example, the hospital would prevent the CO2 Equivalency of 727 metric tons from being exhausted to the atmosphere, which would equate to greenhouse gas emissions from approx. 157 passenger vehicles driven for one year.

What technical preconditions should be met by an anesthesia device to perform low-flow anesthesia? 

When it comes to the delivery of low- and minimal-flow anesthesia, a visual efficiency feedback tool is just the beginning – whether it be an on-screen module or another physical indicator. To help you achieve the benefits of low- and minimal-flow anesthesia delivery and overcome the associated challenges, Dräger takes a comprehensive approach with all of our anesthesia workstations, including the Perseus A500. 

As mentioned, during low- and minimal-flow anesthesia delivery, less fresh enters the breathing system, which also means more warm, humid gas remains in the breathing system. This acclimatized gas can be beneficial for the patient, so it’s important for the anesthesia machine to be optimized for such an environment. To help prevent rainout from occurring in the breathing system in such conditions, Dräger takes a proactive approach by actively heating the entire breathing system on all Draeger anesthesia machines rather than taking a reactive approach by simply trying to collect water in condensers which must be constantly monitored and emptied by staff. In addition, the flow sensors on Dräger anesthesia machines are designed for optimal performance in such conditions. The combination of a heated breathing system and optimized flow sensors make Draeger anesthesia machines ideal for such warm, humid breathing system conditions.

As I mentioned previously, during low- and minimal-flow anesthesia delivery, less fresh gas enters the breathing system so it’s important to prevent any unnecessary losses of gas volume. One way we prevent this is through sample gas recirculation. Another way is by minimizing the leak points on the breathing systems themselves. For the Perseus A500, the breathing system is specifically designed with very few parts and connection points to minimize the chances for leaks. What’s more, the Perseus A500 offers innovative tools to help users quickly identify and resolves leaks should any occur. 

One final point I’d like to make is that the anesthesia machine should mitigate the impact of changes in fresh gas flows on delivered tidal volumes to protect the patient’s lungs. If the need would arise to increase fresh gas flow during a low-flow state, for example, to accelerate washout, all Dräger anesthesia machines including the Perseus A500 prevent that increase of fresh gas flow from impacting the delivered tidal volume. The technology that’s built into all Dräger breathing systems that helps you achieve this patient-protecting benefit is fresh-gas decoupling.  

To learn more about how Dräger anesthesia machines are optimized for low- and minimal-flow delivery, you are certainly welcomed and encouraged to check out our Lung Protective Ventilation website at

How can the Perseus A500 help hospitals monitor and manage their progress toward cost-reduction goals?

To help you monitor and manage performance, anesthetic agent consumption and uptake data is available for export from the Perseus A500 for your EMR. In addition, anesthetic agent consumption and uptake data is also made visible on the display of the Perseus A500 for quick reference. 

Moreover, Dräger just recently launched its Dräger Connect Data Analytics solution, which includes an easy-to-use Gas Consumption Analytics application. When networked with your Perseus A500 fleet, the application offers clinical and economical insights to help you better manage the business and practice of anesthesia care by delivering greater transparency around agent consumption, uptake, efficiency, costs, and fresh gas flow practices. You can use the Gas Consumption Analytics application to monitor and manage your progress toward achieving your goals. To learn more about how Dräger Connect Data Analytics can help you achieve your goals, please visit     

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