Volatile hydrofluorocarbon anesthetics (sevoflurane, isoflurane, and desflurane) and nitrous oxide are ubiquitous in perioperative anesthetic practice and are estimated to contribute between 0.01% to 0.1% of total global greenhouse gas (GHG) emissions (BMJ 2022 8;377:o1301; asamonitor.pub/40kSYby). When used in clinical practice, volatile anesthetics undergo minimal metabolism in the body; an estimated 95% or greater of nitrous oxide, sevoflurane, isoflurane, and desflurane are exhaled from the patient as waste anesthetic gases (WAGs). These WAGs are estimated to make up approximately 50% of perioperative GHG emissions, 5% of total hospital GHG emissions, and can account for 3% of national health care sector GHG emissions (BMJ 2022 8;377:o1301). While scavenging systems in ORs collect these WAGs to minimize occupational exposure, the collected medical waste gases remain chemically unaltered and are often subsequently vented into the atmosphere without further processing. Clinicians have an important role to play in mitigating their emissions.
In 2015, an estimated 266 million anesthetic procedures were performed worldwide, with approximately 36 million surgeries performed in the United States alone (Anesth Analg 2021;133:826-35). The global warming potential of volatile anesthetics and N2O, which measures the heat-trapping properties of a GHG in the environment compared to an equal mass of carbon dioxide over the same time period, demonstrates their potency as GHG contributors. In comparison to the 100-year global warming potential of carbon dioxide, which is calculated to be 1, the global warming potential of inhaled anesthetics was calculated to be 2,540 carbon dioxide equivalents per kilogram for desflurane, 298 for N2O, 510 for isoflurane, and 130 for sevoflurane (asamonitor.pub/40kSYby). Desflurane accounted for approximately 80% of estimated GHG effect from volatile anesthetic waste excluding N2O (Br J Anaesth 2020;125:680-92). Framed in a clinical context, one hour of desflurane has been equated to the automobile emissions of driving 200-400 miles, while one hour of sevoflurane is equivalent to driving eight miles and isoflurane nine to 18 miles (asamonitor.pub/40kSYby). N2O has high global warming potential and is an ozone-depleting agent as well, but it is harder to quantify the exact amount of N2O waste being produced. Not only is N2O frequently used outside the OR in areas such as the labor and delivery floor and in dental clinics, there is significant loss of N2O from central pipelines before it is even used in a clinical setting (Br J Anaesth 2020;125:680-92; Anaesthesia 2022;77:1023-9). Thus, reducing WAG release into the atmosphere is paramount to minimizing the environmental impact of inhaled anesthetics.
Current recommendations for mitigating WAG pollution include utilizing low fresh gas flows, avoiding desflurane and N2O as much as possible, considering TIVA and regional anesthesia where clinically applicable, decommissioning central piping systems for N2O, and using portable N2O canisters that can be closed off between uses (asamonitor.pub/40kSYby; Br J Anaesth 2020;125:680-92; Anaesthesia 2022;77:1023-9). While these recommendations are the gold standard for minimizing WAG pollution, novel environmental technologies to minimize, treat, or reuse WAGs have also been introduced in recent years. For example, the use of automated control of end-tidal anesthetic gas concentration was shown to decrease the GHG emissions over manual control by 44% (Anaesth Intensive Care 2013;41:95-101). Technology for the destruction of WAGs also exists. In Sweden, hospitals capture and destroy N2O waste on a regular basis (Br J Anaesth 2020;125:680-92). In another prototype study, a photochemical exhaust gas destruction system demonstrated successful destruction of desflurane and sevoflurane, though the feasibility of widespread implementation and its net environmental impact reduction remain to be seen (Anesth Analg 2020;131:288-97).
Another method of reducing WAG release has been the implementation of gas capture systems to recycle and reuse volatile anesthetics. While this technology is not as readily available in the U.S., gas capture systems such as CONTRAfluran™ by Zeosys and Baxter and the Deltasorb® and Centralsorb® systems by Blue-Zone Technologies are routinely used across Canada, Europe, and the United Kingdom. The general concept for such systems is the recapture of exhaled gases with specialized filters that are then recycled in the future as ingredients for new anesthetic gases (asamonitor.pub/41ofFw6; asamonitor.pub/40adQSB). Given the relative novelty of gas capture systems, their efficacy in minimizing WAG emissions is uncertain. There is a dearth of studies looking at the efficacy of WAG recapture. One such study from Germany suggests that only 25% of desflurane administered to patients was recaptured using a volatile anesthetic gas capture system and that the majority of desflurane has yet to be exhaled by the patient and cannot be captured after extubation (Br J Anaesth 2022;129:e79-e81). In the cases of inhaled anesthetic use with significant leaks (e.g., mask inductions, mask maintenance, or poorly fitting LMAs), gas similarly can’t be captured. Furthermore, WAG capture systems cannot recapture N2O, thus necessitating an alternate N2O scavenging system that destroys the waste on site. Lastly, regulatory approval is still pending for WAG capture systems in the U.S., as well as allowing recaptured gases to be recycled into new volatile anesthetics.
Despite these limitations of gas capture systems, implementing this technology in clinical practice can be another way to ameliorate the impact of inhaled anesthetics on GHG emissions. The recapture and storage of recaptured WAG canisters still prevent the release of WAGs into the environment, with the hope that they can eventually be repurposed as ingredients in new anesthetic gases. At an institutional level, the implementation of a novel medical device is likely to require review by a multidisciplinary product evaluation committee (comprising representative members from pharmacy, purchasing, anesthesia, nursing, and surgery at our institution). If the proposal is approved for trial use, it will then be evaluated by the product management committee, which is responsible for the logistics of purchasing and implementing the system in several of our ORs. Of course, until such novel technology is perfected, current ASA Committee on Environmental Health recommendations focus on efforts to reduce WAGs and should always be prioritized.