Greenhouse gases: the choice of volatile anesthetic does matter

To the Editor,

Global warming, considered one of the greatest health threats of the 21st century, is linked to greenhouse gas emissions. The major greenhouse gases – carbon dioxide (CO₂), methane, nitrous oxide, and chlorofluorocarbons – have been well studied and regulated. The contributions from the healthcare industry, however, have been largely ignored or excused under the guise of medical necessity.1 Nevertheless, a considerable portion of hospital waste is generated in the operating room, and anesthesiologists are in an ideal position to take a leadership role to minimize the hospital-related negative environmental impact.

Volatile anesthetic drugs are halogenated fluorocarbons and potent greenhouse gases, as measured by their global warming potential (GWP), which is a relative measure of how much heat a given gas traps in the atmosphere compared with a similar mass of CO₂. Because most volatile agents remain in the atmosphere for one to 15 years,2 the GWP is often expressed over a 20-year time horizon (GWP₂₀). This value represents the amount of heat trapped by the gas over a 20-year period, compared with a similar mass of CO₂. For example, the GWP₂₀ values for desflurane, isoflurane, and sevoflurane are 6810, 1800, and 440, respectively.2 The carbon dioxide equivalent (CDE₂₀) is the product of the GWP₂₀ and the quantity of the gas. Colloquially referred to as the “carbon footprint,” it represents the amount of CO₂ that would have the same global warming potential over a 20-year period.

Concerted efforts by the University of British Columbia’s (UBC) Department of Anesthesiology have increased awareness about the deleterious environmental effects of volatile anesthetics. This effort resulted in the purchase of modern, low-flow anesthetic machines that closely regulate expired end-tidal anesthetic gas concentrations. It also contributed to a change in the Department’s preference to use volatile anesthetics with the lowest GWP₂₀ values.

To quantify these changes, we undertook a quality assurance project (Research Ethics Board approval not required as per Article 2.5, TCPS2)¹ to assess the volume of volatile anesthetics used during the years 2012-2016 according to data from seven UBC-affiliated hospital pharmacies.² In 2012, these sites combined used 1,318 L of desflurane and 385 L of sevoflurane. Using published values,2 this resulted in a calculated CDE₂₀ for desflurane and sevoflurane of 13,190,098 kg and 257,655 kg, respectively, for a total of 13.4 million kg of CO₂ equivalence (Figure). Subsequently, the use of desflurane has steadily decreased whereas sevoflurane use increased, such that in 2016, desflurane use was 401 L and sevoflurane use was 772 L. Thus, the calculated CDE₂₀ of 4,009,886 kg for desflurane and 515,979 kg for sevoflurane combined for a total carbon footprint of 4.5 million kg of CO₂ equivalence. Of note, the total volume of volatile anesthetics used decreased from 1,703 L to 1,173 L during this interval. The difference in total CDE₂₀ between 2012 and 2016 was 8.9 million kg, representing a 66% reduction in greenhouse gas emissions (Figure). To put this difference into perspective, 8.9 million kg of carbon emissions is roughly comparable to the annual emissions produced by 1,700 personal vehicles driving an average of 22,000 km per year.3

Figure

Changes in the use of desflurane and sevoflurane, with the resulting environmental impact, during 2012-2016

We encourage anesthesiologists to examine and quantify the environmental impact of their practice. The American Society of Anesthesiologists recently released a comprehensive document on actions that anesthesiologists can adopt to “green” the operating room.4 Suggestions to reduce our carbon footprint included low-flow anesthesia, the use of regional anesthesia and total intravenous anesthesia where possible, and less use of nitrous oxide and desflurane.5 Such changes in practice could substantially reduce an institution’s carbon footprint, as we have demonstrated.