I recently 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.

We passed glacier after glacier that used to fill the fjords we were sailing through, but which now clung to the sides of the canyon walls. Our ship, the National Geographic Explorer, was able to circumnavigate the Svalbard archipelago, something that has rarely been done because the northern ice usually blocks the eastern islands. Those polar bears, and indeed our planet, are in trouble.

However, 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.

When we administer anesthesia, we pay a great deal of attention to the concentration of nitrous oxide and halogenated agents such as sevoflurane or desflurane that our patient receives. We know that too much or too little of these gases can harm our patients. We are often less compulsive about avoiding exposure to ourselves, or even our Operating Room colleagues to waste anesthetic gases. Therefore, to remind everyone of best practices on how to protect ourselves from exposure, I’ve been part of a team collaborating with our Workplace Safety department to create a training video on how to minimize Waste Anesthesia Gas (WAG) exposure.

What Are Waste Anesthesia 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. 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.

What Are The Health Effects of WAGs?

There are health effects of WAGs. Exposure to high concentrations of waste anesthetic gases – even for a short time – may cause difficulties in judgment, loss of coordination, impaired manual dexterity, drowsiness, headache, irritability, fatigue, and nausea. There is evidence that long-term exposure can reduce fertility, and cause neurological, renal and hepatic disease.

Additional Health Risks of Nitrous Oxide

Nitrous oxide has other effects. It irreversibly binds methionine synthetase, the enzyme that regenerates the active form of vitamin B12. Vitamin B12 (cobalamin) is necessary for DNA synthesis and methylation reactions. Its deficiency is associated with anemia, neurologic, psychiatric, hematologic, cardiovascular, and gastrointestinal manifestations. [1]

Ninety minute exposure to 50% nitrous is enough to halve the function of the B12/folate pathway, raising homocysteine levels. Exposure/duration is important. Inhibition of methionine synthetase by nitrous is irreversible. New enzyme must be produced which can take 2-7 days.

Nitrous should be avoided when possible in patients with malnutrition, pernicious anemia, B12/folate deficiencies, and bone marrow suppression, among others. It’s use in serial anesthetics over a short period (less than time frame for regeneration of methionine synthetase) or in really long cases is also questionable.

WAG 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.

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.

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 10 years.

The global warming potential (GWP) of halogenated anesthetics is reported to range from 1230 (isoflurane) to 3714 (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 recently 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.

Protect Yourself From WAG 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.

• 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 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

Protecting The Planet (and Those Polar Bears) From WAGs

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.

At the current time, no matter which anesthetic agent you choose, strict attention to lowering fresh gas flows is the primary method to reduce your contribution to climate change. Be mindful of your flows. It’s very easy to leave the flows at 10 liter/min for extended periods of time at the beginning of the case, or even throughout the case. Again, while the scavenger may take the excess out of the room and protect us, it all ends up in the atmosphere.

Always use the lowest flows appropriate. Having said that, do be aware that for sevoforane there is still some concern about the potential for compound A renal injury [6]. Although compound A renal injury has been documented in rats, it has not been proven in humans. However, the manufacturers package insert for sevoforane still recommends using minimum flows of 2 Liters per minute for cases longer than an hour and no less than 1 liter per minute for shorter cases. Studies are ongoing and hopefully we will have an answer soon.

Because desflurane and nitrous oxide have the highest climate impact, even at low flows, their use should be restricted to cases where they may reduce morbidity and mortality over alternative drugs.

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.

 

May The Force Be With You

Christine E Whitten MD, Author Anyone Can Intubate, 5th Edition

 

References

1. Baum V: When Nitrous Oxide Is No Laughing Matter. http://www2.pedsanesthesia.org/meetings/2007winter/pdfs/Baum-Friday3-9-07-1050am.pdf
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. Mazze RI, MD; Jamison RL: Low-flow (1 l/min) Sevoflurane : Is It Safe. Anesthesiology 6 1997, Vol.86, 1225-1227.