Climate change will be the defining health crisis of the twenty-first century, and environmental health is directly linked with human health. The health sector should lead the sustainability effort by greening itself and reducing its ecological footprint to improve global health and the health of the planet. Anesthesiology has an oversized role in production of greenhouse gases and waste, and thus its impact on affecting change is also oversized. Decreasing the waste of volatile anesthetic agents, medications, and anesthesia equipment is a powerful start to the many sustainability changes needed in health care.
Key points
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Anesthesia providers have the ability to choose an anesthetic plan that minimizes environmental impact without affecting patient care.
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Volatile anesthetic agents are greenhouse gases with significant environmental impacts that can be reduced by choosing to avoid desflurane and nitrous oxide and to use low fresh gas flows.
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Wasted medications and single-use devices, particularly disposable laryngoscopes, contaminate the environment and are a source of considerable cost.
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Anesthesia sustainability initiatives save money and decrease the carbon footprint of the operating room, which is appealing not only to clinicians’ individual sense of responsibility and stewardship but also to the collective duty of physicians to improve global health.
Introduction
Climate change will be the defining health crisis of the twenty-first century and represents the greatest threat to global health. Although severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has captured attention and will be at the forefront of public health measures for the foreseeable future, the effects of climate change on public health are further reaching, longer lasting, and more difficult to mitigate than even this very contagious virus. The scope of the problems arising from climate change is immense, including a rise in sea levels, increases in extreme weather events, increases in atmospheric carbon dioxide (CO 2 ) to unprecedented levels, the spread of infectious diseases, the loss of biodiversity, and the declining health status of the population as a whole. Efforts are underway in many countries to curb CO 2 emissions and thus slow and, it is hoped, eventually reverse the current trends. Ironically, in striving to improve population and individual health, the health care system contributes significantly to climate change, which ultimately negatively affects human well-being. Many analyses have verified the contribution of developed countries’ national health care systems to their countries’ greenhouse gas (GHG) emissions to be between 3% and 10%. The UK National Health Service was estimated to contribute 4.6% of national GHGs in 2015, , whereas an analysis of 36 generally first-world countries as well as India and China found that the health care sector was responsible for an average of 5.5% of each nation’s overall emissions in 2014. The United States is the second-largest emitter of GHGs globally and the US health care sector is responsible for 10% of US GHG emissions. If the US health care sector were a country, it would rank 13th in the world for GHG emissions, ahead of the entire United Kingdom ( Box 1 ). Thus, a decrease in US health care GHG emissions would result in a significant decrease in overall US GHG emissions.
If the US health care sector alone were a country, it would rank 13th in the world for GHG emissions.
In 2012, the Institute of Medicine suggested that the health sector should lead by example by greening itself and reducing its ecological footprint to improve global health and the health of the planet. Anesthesia providers have considerable freedom in making the care plans for patients and it is important to make choices that minimize the environmental impact of anesthetics without affecting the quality of patient care.
The environmental impact of volatile anesthetics, nitrous oxide (N 2 O), intravenous medication waste, single-use devices, and the energy consumption of the heating, ventilation, and air conditioning (HVAC) systems are discussed here, along with practical suggestions to reduce environmental impact.
Volatile anesthetic agents
In response to the growing hole in the ozone layer above Antarctica that formed as a result of atmospheric GHGs, the Montreal protocol of 1987 aimed to phase out global chlorofluorocarbon use, with hydrofluorocarbons subsequently targeted through the 2016 Kigali amendment. Anesthetic gases are chlorofluorocarbons (isoflurane) and hydrofluorocarbons (desflurane, sevoflurane), but volatile anesthetic use was not restricted by either protocol because of medical necessity. In 2014, the release of hydrofluorocarbon and chlorofluorocarbon anesthetic gases was equivalent to 3 million tons of CO 2 , with 80% of the emissions from desflurane alone. GHGs differ in their abilities to trap heat. The effect of this heat trapping over a 100-year period is described using a scale called the global warming potential over 100 years (GWP 100 ), as shown in Table 1 . Although other GHGs, such as methane, are emitted in much larger quantities, the environmental impact of volatile anesthetics is significant because volatile anesthetics have much higher GWP 100 values. For example, despite small quantities, anesthetic gases represented 2% of the United Kingdom’s acute National Health Service organizations’ carbon footprint in 2012. Desflurane has far higher GWP 100 values than the other commonly used agents sevoflurane and isoflurane. The use of desflurane results in nearly 20 times the global warming impact of using sevoflurane. Thus, the choice of volatile agent has the most impact in determining the carbon footprint of an anesthetic ( Box 2 ). To put it in more practical terms, the environmental impact of volatile anesthetics can be expressed in equivalent miles driven in a car per MAC-hour of anesthesia, as shown in Table 2 .
| Atmospheric Lifetime (y) | GWP 100 | |
|---|---|---|
| CO 2 | 5–200 a | 1 |
| Methane (CH 4 ) | 10 | 30 |
| Sevoflurane | 1.1 | 130 |
| Isoflurane | 3.2 | 510 |
| Desflurane | 14 | 2540 |
a No single lifetime can be defined for CO 2 because of the different rates of uptake by different removal processes.
The GHG emissions generated by a 2-hour anesthetic with desflurane (1 L/min fresh gas flow [FGF]) are equivalent to driving a car 608 km (378 miles), roughly the distance from New York City to Akron, Ohio, or from Los Angeles, California, to Phoenix, Arizona. The same anesthetic with sevoflurane (2 L/min FGF) is equivalent to driving 26 km (16 miles).
| Equivalent Miles Driven per MAC-Hour | |
|---|---|
| Sevoflurane | 8 (FGF 2 L/min) |
| Isoflurane | 7 (FGF 1 L/min) |
| Desflurane | 189 (FGF 1 L/min) |
Low Flow
After the choice of volatile anesthetic agent, the fresh gas flow (FGF) rate is the next most important determinant of the carbon footprint of a typical anesthetic ( Box 3 ). Any FGF that exceeds the patient’s needs and the system requirements will be delivered directly out the roof of the hospital via the anesthesia machine’s scavenging system. Thus, the importance of low (<2 L/min) flow cannot be overemphasized. Low flow is most easily accomplished during the maintenance phase of anesthesia. There are several considerations when using low-flow delivery that should be addressed, including the production of compound A and carbon monoxide (CO) and ensuring adequate inspired fraction of oxygen.
Choice of volatile anesthetic agent and the rate of FGF are the most important determinants of the carbon footprint of a gas-based anesthetic.
Compound A is formed by the degradation of sevoflurane by CO 2 absorbents, most notably those containing the strong bases sodium hydroxide and potassium hydroxide (NaOH and KOH) in desiccated conditions. Early studies with sevoflurane found a theoretical risk of nephrotoxicity in humans from compound A. However, the literature does not support the evidence of renal injury caused by compound A in humans undergoing anesthesia. Nevertheless, the US Food and Drug Administration (FDA) has included a warning in the package insert for sevoflurane that states: “sevoflurane exposure should not exceed 2 MAC∙hours at flow rates of 1 to <2 L/min. Fresh gas flow rates of <1 L/min are not recommended.” Although KOH-based CO 2 absorbents are no longer available, NaOH-based CO 2 absorbents are still in use. More modern CO 2 absorbents are calcium hydroxide [Ca(OH) 2 ]–based or lithium hydroxide (LiOH)–based, which interact minimally with sevoflurane but can still produce compound A when dessicated. Overall, the ability to use CO 2 absorbents that do not interact with sevoflurane and the absence of compelling human data that compound A is injurious seem to allow for reasonable doubt regarding FGF limitations with sevoflurane. However, the FDA recommendation mentioned earlier currently still stands and warrants compliance.
CO can be formed by the degradation of any of the volatile agents by desiccated CO 2 absorbents that contain the strong bases NaOH and KOH in large quantities, such as Baralyme and soda lime. Low FGF maintains moisture in the circuit and in the CO 2 absorbent, thus decreasing the risk of CO production with these absorbents. More modern absorbents [Ca(OH) 2 based or LiOH based] do not produce CO when they interact with volatile agents.
Fraction of inspired oxygen (Fi o 2 ) is often set lower in pediatric anesthesia, especially in infants, because of concerns for oxygen toxicity and retinopathy of prematurity. When FGF is also set low, the Fi o 2 may need to be set higher in order to compensate for oxygen extraction. Diligence to the inspired oxygen concentration is of utmost importance to avoid delivering a hypoxic mixture. In addition, side stream gas analyzers often remove 200 mL/min FGF from the circuit, which must be accounted for when using very low FGF, because not all systems return that volume to the circuit after analysis. Low-flow techniques result in more rapid exhaustion of CO 2 absorbent. Contrary to how many anesthesiologists practice, the most efficient use of absorbent results from changing it based on consistently increased inspired CO 2 concentration rather than after a predetermined period of time or with the appearance of an indicator.
The carbon footprint of an anesthetic that uses any volatile agent is dramatically higher than an anesthetic that uses only neuraxial, regional, or intravenous agents ( Fig. 1 ). The GHG emissions that result from using desflurane without N 2 O (discussed later) are approximately 2600 times the emissions that result from an anesthetic using propofol; roughly 32,000 g of CO 2 equivalents (gCO 2 e) versus roughly 12 gCO 2 e. Sevoflurane is far less detrimental to the atmosphere than desflurane, but its use still results in approximately 135 times greater emissions as using propofol (roughly 1600 gCO 2 e versus roughly 12 gCO 2 e). Although the environmental impact of pharmaceuticals is also concerning, it is drastically less than the environmental impact of volatiles, making total intravenous anesthesia the superior choice.
Mask Induction of Anesthesia
Mask induction of anesthesia is unique to pediatrics and presents an additional challenge to minimizing the venting of volatile anesthetic to the atmosphere. In addition, N 2 O is often used during mask induction; this is discussed later. High flows are generally used to facilitate rapid changes in inspired sevoflurane during mask induction, and the resulting wasted anesthesia gas is considerable. Flows need not be higher than 5 to 8 L/min initially during mask induction and should be decreased when uptake by the patient has slowed. This slowed uptake is indicated by the expired agent concentration approaching the inspired concentration until nearly balanced and approximating the desired MAC value. Rebreathing increases when FGF decreases, which may decrease the delivered anesthetic concentration, so vigilance is important during this period. Setting alarm limits for low inspired agent concentration is an easy way to ensure that adequate depth of anesthesia is maintained when FGF is reduced.
Fresh Gas Flow Management During Intubation
When a volatile agent has been initiated before intubation (ie, during induction), it is preferable during intubation to turn off FGF and leave the vaporizer at its set point rather than turn off the vaporizer and leave FGF flowing ( Box 4 ). Leaving FGF on with the circuit disconnected allows washout of volatile agent from the internal volume of the circuit into the room and requires the reestablishment of a volatile agent in the circuit once the circuit is reconnected. The preferable result of turning off FGF instead is the avoidance of environmental contamination during intubation and the ability to use a lower FGF to maintain circuit concentration after intubation. Although the circuit can be refilled quickly with high FGF, the technique of turning off FGF should be carefully considered in high-risk intubation scenarios. This practice requires mindfulness in resuming FGF after intubation, and individual practitioners must decide their comfort levels with this practice.
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