Greenhouse gases (GHGs) are important contributors to global warming because they absorb and trap infrared radiation within the atmosphere. Anesthesiologists use potent GHGs – i.e., hydrofluorocarbons (sevoflurane and desflurane), chlorofluorocarbons (isoflurane), and nitrous oxide. Following their anesthetic use, these gases are scavenged from the anesthetic circuit and expelled into the atmosphere, where they can remain for decades. The global warming potential (GWP100) compares the energy absorbed by 1 ton of a GHG relative to the energy absorbed by 1 ton of CO2 over a 100-year period, with a higher absorbance indicating a worse effect.1 With a GWP100 of 2540, desflurane absorbs far more energy than a comparable amount of CO2.2 Conversely, the GWP100 values for isoflurane, nitrous oxide, and sevoflurane are only 510, 289, and 130, respectively.2

Figure
figure 1

Visual map of the CO2 equivalent for 1 MAC-hour of common anesthetic gases in kilometers driven. A route from Parliament Hill (111 Wellington St, Ottawa, ON, Canada) to Saint Joseph’s Oratory of Mount Royal (3800 Queen Mary Road, Montreal, QC, Canada) was plotted using Google Maps. The total distance is 192 km. The CO2 equivalent of travelling a distance (in kilometers) is calculated by assuming that a car emits 200 g of CO2 per kilometer. Desflurane’s emission is equivalent to the distance driven to Montreal (small blue flag) and half way back to Ottawa (large blue flag). Desflurane (Des) = blue; isoflurane (Iso) = purple; nitrous oxide (N2O) = green; sevoflurane (Sevo) = yellow; MAC-hour = 1 minimum alveolar concentration-hour

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To illustrate the impact of anesthetic gases on the environment, we used calculations from Ryan and Nielsen to convert the GWP100 of each anesthetic gas (at 1 minimum alveolar concentration-hour and fresh gas flow rate of 1 L·min−1) to the grams of CO2 emitted per hour (CO2 equivalent [CDE]).3 The CDE was then converted to the distance (in kilometers) travelled assuming the average car emits 200 g of CO2 per kilometer. The distances displayed in the Figure document an imaginary road trip from Ottawa to Montreal, where:

  • One hour of 2% sevoflurane emits a CDE similar to that driving 6.5 km;

  • One hour of 1.2% isoflurane emits a CDE similar to that driving 14 km;

  • One hour of 60% nitrous oxide emits a CDE similar to that driving 95 km;

  • One hour of 6% desflurane emits a CDE similar to that driving 320 km (a distance equivalent to driving to Montreal and half way back to Ottawa).

Desflurane’s CDE is thus 50 times higher than that of sevoflurane. Anesthesiologists should consider the GWP100 in addition to the clinical and pharmacoeconomic factors when planning an anesthetic. As global citizens, it is our responsibility to find environmentally friendlier and more sustainable ways to practice anesthesia.