To the Editor:
We read with interest the report by McGain et al.,1 comparing the carbon footprint of general versus regional anesthesia. The use of life cycle assessment, quantified as carbon dioxide equivalent emissions, allows thorough analyses to compare the greenhouse effect of different materials.2 Life cycle assessment is very complex and sensitive to its underlying assumptions. It is therefore somewhat surprising that the authors did not include the carbon dioxide equivalent emissions for the production of volatile anesthetics, and in addition used outdated geochemistry values instead of the more recent and more accurate ones.3,4 The two existing synthesis routes increase the carbon dioxide equivalent emissions of sevoflurane by 100% (acetone pathway) and 700% (tetrafluoroethylene pathway; table 1).5 Omitting these emissions significantly underestimates sevoflurane’s environmental impact.
The time frame used by the authors needs to be considered as well. The global warming potential compares the cumulative heat trapping of 1g of a substance to that of 1 g of carbon dioxide during a defined period. The commonly quoted global warming potentials of sevoflurane are those during a 20- and 100-yr period, 702 and 195, respectively.3,6 To compare the greenhouse effect of different molecules, global warming potential during a 100-yr period is most frequently used, and was used by McGain et al. However, the global warming potential during a 100-yr period represents an overly optimistic view, because 99.8% of the total heat absorption by sevoflurane occurs in the first 10 yr after emission, and its effects thus materialize in the first few years.
To illustrate how sensitive a life cycle assessment is to its assumptions, let us consider the impact of 9.6 ml liquid sevoflurane, the hourly consumption reported by McGain et al. (table 1). The carbon dioxide equivalent emissions varies from 1.9 kg to 80.9 kg CO2, depending on the use of older (2011) versus recent (2021) global warming potential values; global warming potential during a 20-yr-period versus a 100-yr-period; inclusion or exclusion of the production emissions; and least versus most wasteful production process. The value reported by McGain et al. may therefore underestimate the carbon dioxide equivalent emissions of sevoflurane by a factor of 46.
Dr. Kalmar has received lecture support, travel reimbursements, equipment loans, or consulting fees from AbbVie (Chicago, Illinois), Getinge (Gothenburg, Sweden), and MEDEC (Aalst, Belgium). Dr. Hendrickx has received lecture support, travel reimbursements, equipment loans, consulting fees, and meeting organizational support from AbbVie, Acertys (Aartselaar, Belgium), Air Liquide (Paris, France), Allied Healthcare (St. Louis, Missouri), Armstrong Medical (Coleraine, UK), Baxter (Deerfield, Illinois), Dräger (Lübeck, Germany), General Electric Healthcare (Madison, Wisconsin), Getinge, Hospithera (Anderlecht, Belgium), Heinen und Lowenstein (Bad Ems, Germany), Intersurgical (Wokingham, UK), MDoloris Medical Systems (Loos, France), MEDEC, Micropore (Elkton, Maryland), Molecular Products (Louisville, Colorado), NWS, Philips (Brussels, Belgium), Piramal (Mumbai, India), and Quantium Medical (Barcelona, Spain). The other author declares no competing interests.