Anaesthesia
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Observational Study
Reducing the carbon footprint of general anaesthesia: a comparison of total intravenous anaesthesia vs. a mixed anaesthetic strategy in 47,157 adult patients.
Global warming is a major public health concern. Volatile anaesthetics are greenhouse gases that increase the carbon footprint of healthcare. Modelling studies indicate that total intravenous anaesthesia is less carbon intensive than volatile anaesthesia, with equivalent quality of care. ⋯ The carbon dioxide equivalent footprint of hypnotic drugs per intervention in the hospital using the total intravenous anaesthesia strategy was 20 times lower than in the hospital using the mixed strategy (emissions of 2.42 kg vs. 48.85 kg carbon dioxide equivalent per intervention, respectively). The total intravenous anaesthesia strategy significantly reduces the carbon footprint of hypnotic drugs in general anaesthesia in adult patients compared with a mixed strategy. Further research is warranted to assess the risk-benefit ratio of the widespread adoption of total intravenous anaesthesia.
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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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The environmental emissions attributed to anaesthetic nitrous oxide across the NHS are comparable to the carbon dioxide released by 135,000 flights from Frankfurt to New York. Much of these emissions are attributable to cumbersome and inadequately managed piped systems, resulting in excessive loss and waste. ⋯ Nitrous oxide mitigation efforts by grassroots and professional advocacy networks are enhanced through national centralised emission monitoring, distribution of data, technical information and provision of quality analysis. Given the climate harms of nitrous oxide, concerted efforts should be made to rationalise its use, and resources should be committed to supporting this at local, regional and national levels.
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In 2020 the NHS in England set a target of reaching net zero carbon emissions by 2040. Progress has already been made towards this goal, with substantial reductions in the use of environmentally harmful anaesthetic gases, such as desflurane, in recent years. ⋯ Reducing unwarranted variation can improve patient care and service efficiency, and can also support the drive to net zero. In this article we set out what the GIRFT programme is doing to support sustainable healthcare in England, why it is uniquely positioned to support this goal and what the future challenges, barriers, enablers and opportunities are likely to be in the drive to net zero.