We endorse the proposal to adopt a framework for cost-effective decision-making to optimise the use of limited economic resources [1]. Additionally, we fully support the notion of prioritising measures with the greatest and most efficient impact first, based on quantitative analysis. However, it is unclear to us how the reported 47 kg carbon dioxide equivalents (CO₂e) for one bottle of sevoflurane were determined.

The most recent Intergovernmental Panel on Climate Change (IPCC) report provides the global warming potential over 100 years (GWP₁₀₀) and 20 years (GWP₂₀) of sevoflurane as 195 and 702, respectively [2]. Sevoflurane has a specific gravity of 1.52 g.ml^-1. Thus, 1 ml of sevoflurane, weighing 1.52 g, will cause an amount of global heating as much as 296 g carbon dioxide would over a 100-year time horizon, or what 1067 g carbon dioxide would cause over a 20-year time horizon. With an atmospheric lifetime of 1.9 years, 99.5% of this energy, amounting to 18,354 megajoules, is irreversibly absorbed within the first 10 years [2].

Given the looming risk of exceeding climate tipping points in the coming years and the various positive feedback mechanisms whereby initial warming leads to additional greenhouse gas emissions and further warming acceleration, there are compelling arguments for adopting a 20-year time horizon. If only being looked at from a purely medical perspective, it is also increasingly clear that climate change threatens our health and survival within decades, not centuries [3]. However, if for political expediency one is more concerned with prioritising international accounting over the climatological reality in the coming decades, a 100-year time horizon may be more convenient. When production emissions are also factored into the assessment, the scope 1 emissions, which represent the local emissions at the hospital itself, more than double [4]. This implies that one bottle of 250 ml sevoflurane corresponds to 161 kg carbon dioxide over a 100-year time horizon and 579 kg carbon dioxide over a 20-year time horizon.

The carbon dioxide emissions associated with managing recovery must also be considered. A lifecycle analysis compliant with ISO 14040 standards concludes that the production, transport, desorption and recycling/disposal of 1 kg of captured volatile anaesthetics using CONTRAfluran™ (ZeoSys, Luckenwalde, Germany) results in emissions totalling 45.4 kg of CO₂e [5]. Capturing emissions from one bottle of 250 ml (or 380 g) sevoflurane results in emissions equivalent to 17 kg of CO₂e. Furthermore, it is highly speculative as to what extent captured sevoflurane will be effectively reused or merely destroyed. While responsible destruction effectively mitigates scope 1 pollution from hospital venting, this does not take into account emissions from the production of the captured sevoflurane. Consequently, although capturing 250 ml of sevoflurane prevents scope 1 emissions of 267 kg CO₂e, it fails to address scope 3 emissions, which represent the total emissions resulting from the production and transportation of sevoflurane, of 312 kg CO₂e [4]. Yet, even with volatile anaesthetic capture and refinement for reuse, a 10% loss during the recovery process necessitates accounting for the remaining scope 3 emissions of 31 kg CO₂e [5, 6].

This underscores that accounting for the saved emissions involves numerous speculative assumptions. The following illustrates the range of emissions saved, from 57 to 531 kg CO₂e, through the capture of 0.250 l of sevoflurane. Using a 100-year time horizon and without recycling, the savings amount to 57 kg CO₂e (calculated as 0.250 × 1.52 × 195 − 17). When assuming a 20-year time horizon and recycling 90% of captured sevoflurane [5], the savings total 531 kg CO₂e. This calculation comprises 0.250 × 1.52 × 702 kg for scope 1 emissions, plus 0.250 × 1.52 × 702 × 1.17 × 0.9 kg for scope 3 emissions and subtracting 17 kg for CONTRAfluran™ lifecycle emissions. Depending on the assumptions, investing in capture techniques may be worthwhile compared with the average price for carbon dioxide emission permits in 2023, which was €86 (US$93, £73) per ton under the European Union Emissions Trading System.

However, we must emphasise that this should be the final option, only pursued after fully capitalising on all other avenues, which are already recognised for their combined economic and ecological benefits. Investing in advanced workstations capable of automatic minimal-flow can yield significantly greater climate benefits and substantial financial savings [7]. Similarly, using total intravenous anaesthesia whenever clinically feasible, not only leads to substantial financial savings compared with even minimal-flow volatile anaesthesia but also reduces the climate impact by over 90%.

Notwithstanding the adjusted climate impact assessments and the consideration of various uncertainties, we echo Leslie and Silverman's plea for a rational decision-making framework to ensure that all investments contribute to the most significant possible reduction in the nation's carbon footprint, even as we advocate for broadening the scope of decision-making.

我们赞同采用具有成本效益的决策框架以优化有限经济资源的利用的提议[ 1 ]。此外，我们完全支持基于定量分析优先考虑影响最大、最有效的措施的理念。然而，我们尚不清楚所报道的一瓶七氟醚的47 千克二氧化碳当量 (CO _{2 e) 是如何确定的。}

最新的政府间气候变化专门委员会 (IPCC) 报告提供了七氟烷 100 年 (GWP ₁₀₀ ) 和 20 年 (GWP ₂₀ ) 的全球变暖潜力分别为 195 和 702 [ 2 ]。七氟醚的比重为1.52g.ml ^-1。因此，1 毫升重 1.52 克的七氟醚在 100 年内所造成的全球变暖相当于 296 克二氧化碳在 100 年内造成的热量，或者 1067 克二氧化碳在 20 年内所造成的热量。大气寿命为 1.9 年，其中 99.5%（总计 18,354 兆焦耳）的能量在前 10 年内被不可逆地吸收[ 2 ]。

鉴于未来几年超过气候临界点的迫在眉睫的风险，以及初始变暖导致额外温室气体排放和进一步加速变暖的各种积极反馈机制，有令人信服的理由支持采用 20 年的时间范围。如果仅从纯粹的医学角度来看，气候变化将在几十年而不是几个世纪内威胁我们的健康和生存，这一点也越来越明显[ 3 ]。然而，如果出于政治上的权宜之计，人们更关心未来几十年的国际核算优先于气候现实，那么 100 年的时间范围可能更方便。当生产排放也纳入评估时，范围 1 排放（代表医院本身的当地排放）增加了一倍以上 [ 4 ]。这意味着一瓶 250 毫升七氟烷在 100 年时间内相当于 161 公斤二氧化碳，在 20 年时间内相当于 579 公斤二氧化碳。

还必须考虑与管理恢复相关的二氧化碳排放。符合 ISO 14040 标准的生命周期分析得出结论，使用 CONTRAfluran™（ZeoSys，Luckenwalde，德国）生产、运输、解吸和回收/处置 1 kg 捕获的挥发性麻醉剂会导致排放总量为 45.4 kg CO ₂ e [ 5 ] 。捕获一瓶 250 毫升（或 380 克）七氟烷的排放量相当于 17 公斤 CO ₂ e 的排放量。此外，对于捕获的七氟醚在多大程度上将被有效地再利用或仅仅销毁，存在很大的推测性。虽然负责任的销毁有效地减轻了医院通风造成的 1 类污染，但这并没有考虑到捕获的七氟醚生产过程中的排放。因此，虽然捕获 250 ml 七氟醚可以防止 267 kg CO ₂ e 的范围 1 排放，但无法解决 312 kg CO ₂ e 的范围 3 排放，即七氟醚生产和运输产生的总排放量 [ 4 ] 。然而，即使采用挥发性麻醉剂捕获和精炼以供再利用，回收过程中 10% 的损失也需要考虑剩余的 31 kg CO ₂ e 范围 3 排放量 [ 5, 6 ]。

这强调了对节省的排放量的核算涉及许多推测性假设。下图说明了通过捕获 0.250 升七氟烷所节省的排放量，从 57 到 531 kg CO ₂ e。以 100 年为时间范围，在不进行回收的情况下，可节省 57 kg CO ₂ e（计算公式为 0.250 × 1.52 × 195 − 17）。假设 20 年的时间范围并回收 90% 的捕获七氟烷 [ 5 ]，总共可节省 531 kg CO ₂ e。该计算包括范围 1 排放量的 0.250 × 1.52 × 702 kg，加上范围 3 排放量的 0.250 × 1.52 × 702 × 1.17 × 0.9 kg，并减去 CONTRAfluran™ 生命周期排放量的 17 kg。根据假设，与 2023 年二氧化碳排放许可证的平均价格（欧盟排放交易体系下每吨 86 欧元（93 美元，73 英镑））相比，投资捕集技术可能是值得的。

然而，我们必须强调，这应该是最终的选择，只有在充分利用所有其他途径后才可采用，这些途径的综合经济效益和生态效益已经得到认可。投资具有自动最小流量功能的先进工作站可以显着带来更大的气候效益并节省大量资金[ 7 ]。同样，只要临床可行，就使用全静脉麻醉，与微量挥发性麻醉相比，不仅可以节省大量资金，而且还可以减少 90% 以上的气候影响。

尽管调整了气候影响评估并考虑了各种不确定性，但我们赞同莱斯利和西尔弗曼的呼吁，即建立一个合理的决策框架，以确保所有投资都有助于最大程度地减少国家碳足迹，即使我们主张扩大碳足迹决策的范围。