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Global Warming Potential of Inhaled Anesthetics: Application to Clinical Use
Skip to main page content HOME CURRENT ISSUE PAST ISSUES CME SUBSCRIBE ONLINE HELP SUBMIT TO A&A ACTIVATE MY ACCOUNT Search GO Advanced Search ? User Name Password Sign In Global Warming Potential of Inhaled Anesthetics: Application to Clinical Use Susan M. Ryan, MD, PhD* and Claus J. Nielsen, CSc?
From the *Department of Anesthesia and Perioperative Care, University of California, San Francisco, San Francisco, California; and ?Department of Chemistry, Centre for Theoretical and Computational Chemistry, University of Oslo, Oslo, Norway. Address correspondence to Susan M. Ryan, MD, PhD, 505 Parnassus Ave., Box 0648, University of California, San Francisco, San Francisco, CA 94143. Address e-mail to ryans{at}anesthesia.ucsf.edu. Abstract BACKGROUND: Inhaled anesthetics are recognized greenhouse gases. Calculating their relative impact during common clinical usage will allow comparison to each other and to carbon dioxide emissions in general. METHODS: We determined infrared absorption cross-sections for sevoflurane and isoflurane. Twenty-year global warming potential (GWP20) values for desflurane, sevoflurane, and isoflurane were then calculated using the present and previously published infrared results, and best estimate atmospheric lifetimes were determined. The total quantity of each anesthetic used in 1 minimal alveolar concentration (MAC)-hour was then multiplied by the calculated GWP20 for that anesthetic, and expressed as “carbon dioxide equivalent” (CDE20) in grams. Common fresh gas flows and carrier gases, both air/oxygen and nitrous oxide (N2O)/oxygen, were considered in the calculations to allow these examples to represent common clinical use of inhaled anesthetics. RESULTS: GWP20 values for the inhaled anesthetics were: sevoflurane 349, isoflurane 1401, and desflurane 3714. CDE20 values for 1 MAC-hour at 2 L fresh gas flow were: sevoflurane 6980 g, isoflurane 15,551 g, and desflurane 187,186 g. Comparison among these anesthetics produced a ratio of sevoflurane 1, isoflurane 2.2, and desflurane 26.8. When 60% N2O/40% oxygen replaced air/oxygen as a carrier gas combination, and inhaled anesthetic delivery was adjusted to deliver 1 MAC-hour of anesthetic, sevoflurane CDE20 values were 5.9 times higher with N2O than when carried with air/O2, isoflurane values were 2.9 times higher, and desflurane values were 0.4 times lower. On a 100-year time horizon with 60% N2O, the sevoflurane CDE100 values were 19 times higher than when carried in air/O2, isoflurane values were 9 times higher, and desflurane values were equal with and without N2O. CONCLUSIONS: Under comparable and common clinical conditions, desflurane has a greater potential impact on global warming than either isoflurane or sevoflurane. N2O alone produces a sizable greenhouse gas contribution relative to sevoflurane or isoflurane. Additionally, 60% N2O combined with potent inhaled anesthetics to deliver 1 MAC of anesthetic substantially increases the environmental impact of sevoflurane and isoflurane, and decreases that of desflurane. N2O is destructive to the ozone layer as well as possessing GWP; it continues to have impact over a longer timeframe, and may not be an environmentally sound tradeoff for desflurane. From our calculations, avoiding N2O and unnecessarily high fresh gas flow rates can reduce the environmental impact of inhaled anesthetics. Footnotes Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (www.anesthesia-analgesia.org). Disclosure: The authors report no conflicts of interest. Reprints will not be available from the author. Copyright ? 2010 International Anesthesia Research Society ? Previous | Next Article ?Table of Contents This Article Published online before print June 2, 2010, doi: 10.1213/?ANE.0b013e3181e058d7 A & A July 2010 vol. 111 no. 1 92-98 ? Abstract Full Text Full Text (PDF) Classifications Anesthetic Pharmacology Services Email this article to a colleague Alert me when this article is cited Alert me if a correction is posted Similar articles in this journal Similar articles in PubMed Download to citation manager Request Permissions Citing Articles Load citing article information Citing articles via Google Scholar Google Scholar Articles by Ryan, S. M. Articles by Nielsen, C. J. Search for related content PubMed PubMed citation Articles by Ryan, S. M. Articles by Nielsen, C. J. Related Content Economics and Health Care Research Mechanisms Ethics Pharmacology Load related web page information Current Issue June 2011, 112 (6) 
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