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Created July 17, 2019, last updated 2 months ago.
Collection: 100, Score: 1394, Trend score: 0, Read count: 1966, Articles count: 10, Created: 2019-07-17 23:56:56 UTC. Updated: 2024-09-14 22:33:52 UTC.Notes
Also see Carbon Footprint from Anaesthetic gas use [pdf] from the UK’s Sustainable Development Unit.
Daniel Jolley
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Collected Articles
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Although the increasing abundance of CO(2) in our atmosphere is the main driver of the observed climate change, it is the cumulative effect of all forcing agents that dictate the direction and magnitude of the change, and many smaller contributors are also at play. Isoflurane, desflurane, and sevoflurane are widely used inhalation anaesthetics. Emissions of these compounds contribute to radiative forcing of climate change. To quantitatively assess the impact of the anaesthetics on the forcing of climate, detailed information on their properties of heat (infrared, IR) absorption and atmospheric lifetimes are required. ⋯ On the basis of the derived 100 yr GWPs, the average climate impact per anaesthetic procedure at the University of Michigan is the same as the emission of ∼22 kg CO(2). We estimate that the global emissions of inhalation anaesthetics have a climate impact which is comparable with that from the CO(2) emissions from one coal-fired power plant or 1 million passenger cars.
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Anesthesia and analgesia · Jul 2010
Global warming potential of inhaled anesthetics: application to clinical use.
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. ⋯ 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.
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Anesthetic drugs have the potential to contribute to global warming. There is some debate about the overall impact of anesthetic drugs relative to carbon dioxide, but there is no question that practice patterns can limit the degree of environmental contamination. In particular, careful attention to managing fresh gas flow can use anesthetic drugs more efficiently--reducing waste while achieving the same effect on the patient. ⋯ This article provides background information and discusses strategies for managing fresh gas flow during each phase of anesthesia with the goal of reducing waste when using a circle anesthesia system. Monitoring oxygen and anesthetic gas concentrations is essential to implementing these strategies safely and effectively. Future technological advances in anesthetic delivery systems are needed to make it less challenging to manage fresh gas flow.
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“Inhalational anaesthetic agents are chlorofluorocarbons, ‘greenhouse gases’ that have between 349 (sevoflurane) and 3714 (desflurane) times the global warming potential over a 20 year time horizon of carbon dioxide (isoflurane 1401), equivalent to driving a car 18 (sevoflurane) to ~350 miles (desflurane) per hour of anaesthetic use (isoflurane 30 miles); these figures do not account for the additional carbon cost of heating desflurane vaporisers. Together with nitrous oxide, inhalational anaesthetic agents contribute ~2.5% of the 22.8 million tonnes of carbon dioxide equivalents the NHS produces annually.” - White
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Nitrous oxide (N2O), like carbon dioxide, is a long-lived greenhouse gas that accumulates in the atmosphere. Over the past 150 years, increasing atmospheric N2O concentrations have contributed to stratospheric ozone depletion1 and climate change2, with the current rate of increase estimated at 2 per cent per decade. Existing national inventories do not provide a full picture of N2O emissions, owing to their omission of natural sources and limitations in methodology for attributing anthropogenic sources. ⋯ Our findings point to growing N2O emissions in emerging economies-particularly Brazil, China and India. Analysis of process-based model estimates reveals an emerging N2O-climate feedback resulting from interactions between nitrogen additions and climate change. The recent growth in N2O emissions exceeds some of the highest projected emission scenarios3,4, underscoring the urgency to mitigate N2O emissions.
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Nitrous oxide is now recognised as an important contributor to the 'greenhouse' effect. Each year the medical profession unwittingly adds a very small burden of this gas to the atmosphere. Unfortunately, the long lifetime of nitrous oxide means that all emissions into the atmosphere are significant. By making small changes in their practices, anaesthetists are well-placed to help reduce the potential environmental damage.
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Global Warming Potential vs Radiative Forcing
Global warming potential is "...the ratio of the cumulative radiative forcing (the energy being added to the planet, based on radiative efficiency and lifetime) over a time horizon from the instantaneous release of 1 kg of a given gas, such as desflurane, relative to that of 1 kg of carbon dioxide." A 100 year time horizon is commonly used as GWP100, reflecting the long lifetime of CO2, representing the warming potential of a single emission of a gas compared to the same mass of CO2. GWP is then used to derive CO2-equivalents.
Although GWP allows a simplistic comparison of greenhouse gases (eg. desflurane GWP 2530), it is misleading to use it to assess the climate impact of volatile anaesthetic agents primarily because of their short lifetimes, but also because "GWP does not consider the actual atmospheric abundance of a greenhouse gas, nor does it represent any of the physical complexity of the overall climate system..."
"Based on climate science, we assert that this is a physically unsound approach for determining the potential climate impact of volatile anaesthetic gases, and that it is the atmospheric concentration and radiative forcing of individual greenhouse gases that matter..." – Slingo & Slingo.
Instead climate scientists today prefer to use radiative forcing, "... the difference between the energy entering the planet and the energy leaving it..."
The percentage contribution of all volatile anaesthetic gases to radiative forcing is <0.01% compared to that from carbon dioxide. In comparison, the global emission reductions due to the COVID-19 lockdown were almost 1000x greater than the cumulative impact from anaesthetic volatile gases, and yet this reduction was undetectable above normal climate variability.
Atmospheric concentration (ppt) Atmospheric lifetime (y) (Effective) radiative forcing (Wm-2) Carbon dioxide 420,000,000 100+ 2.16 Methane 1,920,000 12.4 0.54 Nitrous oxide 336,000 123 0.21 Desflurane 0.37 14.1 0.00017 Sevoflurane 0.16 1.4 0.00003 Isoflurane 0.11 3.5 0.00006 "On the basis of GWP, anaesthetic gases appear to be very 'damaging'. However, this conclusion is scientifically unsound: their lifetimes are short; their emissions, accumulation and resulting atmospheric concentrations are minute; and their actual radiative forcing is vanishingly small."
More complexity...
Beyond the over-simplification of GWP and CO2e, Slingo & Slingo also explore the challenge in linking the minute radiative forcing of volatile anaesthetic gases to actual climate change and impact.
summary"...future warming will be determined by how successful we are in controlling our direct carbon dioxide emissions. ... While changing a vaporiser feels achievable and tangible, the scientific reality is inconsequential when we consider all the steps from GWP to climate impact. ... It is carbon dioxide emissions that will define our future, not the use of volatile anaesthetic agents."
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