Few of us think about the impact of our anesthetic waste gas on global warning. When we administer anesthesia, we pay a great deal of attention to the concentration of nitrous oxide and halogenated agents that our patient receives. We know that too much or too little of these gases can harm our patients. We may worry about safety effects of anesthetic waste gas on ourselves and our OR colleagues. But global warming?

As we approach a new academic year, let’s help our trainees establish safe practices, not just for our patients, but for the planet. For a separate discussion of why minimizing anesthesia waste gas exposure is so important to our own health, see:

Minimizing Anesthesia Waste Gas Exposure: Hazards and Good Practices.

Years ago, I took part of a team collaborating with our Workplace Safety department to create a training video on how to minimize Waste Anesthesia Gas (WAG) exposure. That link is here.

Anesthesia Waste Gases and Global Warming

In 2018 I had the incredible opportunity to visit Svalbard, Norway, an archipelago above the Arctic Circle about 600 miles from the North Pole. We were lucky enough to see polar bears, including a rare sighting of a Mom with 3 cubs. The landscape was breathtakingly beautiful. But underlying the minute to minute magic was the sober message that the climate was warming and the ice was melting. The glaciers were disappearing.

I came home comfortable in my own mind that I was already doing my part to decrease global warming: using LED light bulbs, solar power, hybrid car, turning off all electrical devices when not in use. Ironically, I soon discovered that the anesthetic gases I use every day are some of the most potent greenhouse gases on the planet. Sadly, some of my routine practices at that time were contributing to the problem.

The anesthetic waste gases, volatile anesthetics and nitrous oxide, contribute to depletion of the ozone layer. Some have heat trapping properties (global warming potential) 2,540 times higher compared to CO2 and last for years in the atmosphere.

What Are Waste Anesthetic Gases?

Waste anesthesia gases are the anesthetic gases and vapors that leak into the surrounding room from the patient’s anesthetic breathing circuit during medical procedures. These gases are so potent that trace gas exposure is typically measured in parts per million. 1% of an anesthetic gas equals 10,000 parts per million. Anesthetic waste gases consist of:

• gases and vapors that leak into the surrounding treatment room from the patient’s anesthetic breathing circuit during medical procedures
• gases expelled from the building as part of the scavenger system
• gases exhaled by the patient in the recovery room period

Our goal is to minimize exposure to these waste anesthetic gases to less than 2 parts per million of the halogenated agents and less than 25 parts per million of nitrous oxide. That can be done with attention to small details during the anesthetic and use of a scavenging system. An additional problem, as we shall see, is that getting the gases out of the room, and away from us, doesn’t get them out of the atmosphere where they can do some real harm.

Waste Anesthesia Gas Greenhouse Effect

It turns out that being incautious with waste anesthetic gases in our anesthetic practice can also significantly impact greenhouse gas emissions and therefore climate. Exhaled anesthetic gas is minimally metabolized by the body before it enters any scavenger system. The exhaled gas, as well as gases which bypass the patient in the circuit, both end up in the atmosphere where they remain unaltered for a very long time.

We have all heard the risks of chlorofluorocarbons (CFCs) and depletion of the ozone layer. CFCs can last for 100 years in the upper atmosphere. N20, along with CO2 and methane, are the most influential greenhouse gases mentioned in the Kyoto accords [2]. N2O is a potent destroyer of ozone.

Global Warming Potential (GWP)  is a measure of how much energy the emissions of 1 ton of a gas will absorb over a given period of time, relative to the emissions of 1 ton of carbon dioxide (CO₂). The larger the GWP, the more that a given gas warms the Earth compared to CO₂over that time period. The time period usually used for GWPs is 100 years. The table above shows that a gas like Desflurane has a GWP 2,540 times greater than CO2. It also remains in the atmosphere for 14 years after release. Nitrous oxide has a warming effect 273 times that of CO2, and lasts for 114 years in atmosphere. These are staggeringly high and long effects.

Nitrous Oxide

There are many non-anesthetic sources of nitrous oxide in the atmosphere, including agriculture (nitrogen based fertilizers) and the use of fossil fuels. The precise amount of N2O from anesthesia use is unknown but has been estimated at about 3% of the total. However, a small percentage of a big number is still a big number. One study estimates that approximately 35,000 tons of N2O were used for 70 million anesthetics in the United States alone in 2006 [3]. Considering that each N20 molecule lasts for as long as 114 years in the upper atmosphere, our anesthetic practice can cause considerable climate impact.

For a discussion of health risks from using nitrous oxide see Nitrous Oxide: Safe to Use?.

Halogenated Agents

By measuring the rate of reaction with hydroxyl radicals, the tropospheric lifetimes of halothane, enflurane, and isoflurane have been calculated at 2, 6, and 5 years, respectively [5]. Not as long as nitrous, but certainly long enough to cause damage. Desforane lasts upwards of 14 years.

The global warming potential (GWP) of halogenated anesthetics is reported to range from 539 (isoflurane) to 2,540 (desflurane) times the GWP of carbon dioxide (CO2) [2]. Desflurane accounts for the largest life cycle impact among the anesthetic drugs: 15 times that of isoflurane and 20 times that of sevoflurane on a per MAC-hour basis when administered in an O2/air admixture [3]. Of note, Yale-New Haven Hospital removed Desflurane from its formulary, based largely on the environmental impact findings of their recent study as well as the fact that it is the most costly of the agents.

Minimize Anesthetic Waste Gas Exposure

Do not rely on your sense of smell to protect you, or the planet. Anesthetic gases cannot be detected by smell until concentrations are very high. For example, Halothane cannot be smelled by 50% of the general population until the concentration is 125 times the NIOSH recommended exposure limit of 2 ppm.

The main goals are to use the least flow and the lowest concentration of gas appropriate to the clinical situation. Minimize anesthesia waste gas release by:

• Ensure your scavenging system is working and machine connections are tight
• Make sure the filler cap is tight when filling the vaporizer, Stop filling before the line and then wait a few seconds before removing the filler cap and agent bottle from the cassette.
• Avoid spilling liquid anesthetic – clean any spills promptly and properly.
• Close the breathing circuit before you prefill it.
• With any anesthetic, pediatric or adult, minimize disconnections to the circuit while anesthetic is flowing. Either turn off the vaporizer, decrease flows, or plug the circuit.
• For maintenance, use the lowest flows appropriate. The minimal recommended flow may vary depending on the agent, and circuit, used. Decreasing total amount of anesthetic vaporized not only helps protect you and your staff, it decreases global warming.
• Toward the end of the case, use high flow oxygen to wash anesthetic into the scavenger system.
• If you disconnect to flush the circuit, close the end of the hose to prevent gas escape. Flush the bag into the circuit

Total Intravenous Anesthesia

Total Intravenous Anesthesia (TIVA) is becoming more popular but is certainly not a panacea. Although newer anesthetic agents, such as xenon are being studied, and new scavenger systems that bind the gas molecules and prevent their release are under investigation, use of anesthetic gases will continue for some time. For babies and children inhalation agents are currently the best option.

Obviously, elimination of anesthetic gases are not an option at this time, however there are things we can do to decrease the amounts and types of gases released.

Protecting The Planet (and Those Polar Bears)

When I got back from the Arctic, I reassessed my practice and found my anesthesia waste gas contamination was high. At that time I was still using nitrous oxide, not having yet discovered some of the significant health risks it can cause. I loved Desflurane for adults. I did high flow, “blow by” inductions for pediatric patients. I used high flows during induction but did not decrease or stop those flows during intubation, allowing gas to flow into the room.

Afterward, I significantly changed my practice. I rarely use nitrous at all. I reserve Desflurane only for those cases where it’s unique properties are truly clinically indicated. And I use the lowest flows whenever possible. I still use high flows during induction but I lower the flows to 100 ml/min during intubation and try to block the mask. After intubation I increase the flows again. Of note: I never turn flows completely off to prevent me from being distracted and failing to turn them back on.

Knowledge is power. Now that we know that there is a potential connection with the environment, as well as our personal health, we can start by being more mindful in our anesthetic practice. We can and must all do our part to minimize anesthetic waste gas.

 

May The Force Be With You

Christine E Whitten MD,
Author: Anyone Can Intubate, A Step-By-Step Guide, 5th Edition
and
Pediatric Airway Management: A Step-By-Step Guide

References

1.   Ryan SM, Nielsen CJ. Global warming potential of inhaled anesthetics: application to clinical use. Anesth Analg. Jul 2010;111(1):92-8. doi:10.1213/ANE.0b013e3181e058d7
2. Kyoto Protocol to the United Nations Framework Convention on Climate Change. New York: United Nations, 1998. http://unfccc.int/resource/docs/convkp/kpeng.pdf. Accessed 9/17/2010
3. Ishizawa Y: General Anesthetic Gases and the Global Environment. Anesth Analg 2011;112:213–7
4. Sherman J ; Le C; Lamers, V; Eckelman, M: Life Cycle Greenhouse Gas Emissions of Anesthetic Drug. Anesthesia & Analgesia: May 2012 – Volume 114 – Issue 5 – p 1086–1090
5. Brown AC, Canosa-Mas CE, Parr AD, Pierce JM, Wayne RP. Tropospheric lifetimes of halogenated anaesthetics. Nature 1989;341:635–7
6. Devlin-Hegedus JA, McGain F, Harris RD, Sherman JD. Action guidance for addressing pollution from inhalational anaesthetics. Anaesthesia. 2022 Sep;77(9):1023-1029. doi: 10.1111/anae.15785. Epub 2022 Jun 21. PMID: 35729804; PMCID: PMC9543086.

Note: this article originally published in 2016 as “Can Changing Our Anesthesia Practice Help Save The Polar Bears