Journal article summary - The carbon footprint of general anaesthetics: A case study in the UK

The carbon footprint of general anaesthetics: A case study in the UK

Xiaocheng Hu, JM Tom Pierce, Tim Taylor, Karyn Morrissey

Resources, Conservation & Recycling 167 (2021) 105411

Background and introduction

The NHS accounts for 5.4% of national greenhouse gas emissions, and approximately 5% of that comes from waste anaesthetic gases. A target to reduce anaesthetic gas use is included in ‘A Greener NHS’ plan, published in October 2020. Vapour capture technology aims to capture and recycle anaesthetic gases, reducing their environmental impact. 

This paper has three stated aims;

1. To assess the carbon footprint of inhalation anaesthetic gases (IAGs) and compare to propofol.
2. To assess the impact of vapour capture technology (VCT) on the carbon footprint of IAGs.
3. To provide an overall carbon footprint of general anaesthetics in the U.K.

Methods

The authors used Life Cycle Inventory analysis to examine the carbon footprint of the IAGs from ‘cradle to grave’. Interestingly, the paper considers the impact different manufacturing processes has. As direct information on manufacture was not available, product patents were used to model the manufacturing process.

Different scenarios were used for modelling the volumes of IAGs used, including the use of nitrous oxide along with oxygen as a carrier gas for the IAGs, and for different flow rates of the carrier gases. 

Calculating the reduction in the footprint of IAGs with the introduction of VCT is challenging, as some gas will be recycled, but some ‘new’ gas will also be needed. As an estimation, the authors assumed gases will be recycled once, using one hour of ‘new’ IAG then one hour of 70% recycled and 30% ‘new’ IAG, and then averaged that amount over an hour.

Data for UK-wide IAG use was estimated from usage received by 193 of the 254 trusts nation-wide. This data was then used to model usage based on the same scenarios used previously.  

Results

Desflurane has the largest carbon footprint, though potentially if sevoflurane is administered with nitrous oxide at higher flow rates, its carbon footprint approaches that of desflurane, particularly if its manufacture uses tetrafluoroethylene. Avoiding this intermediary reduces sevoflurane’s carbon footprint by 84%. The manufacture of isoflurane and desflurane have much smaller relevance to their carbon footprint. 

Unsurprisingly, using VCT has the greatest impact when used alongside the most environmentally harmful gas, desflurane. If using VCT in combination with sevoflurane, no nitrous oxide and a low-flow technique (0.5L/min) then the carbon footprint of that anaesthetic could be less than a propofol-based anaesthetic.

UK-wide usage in 2018 shows total sevoflurane use has a similar carbon footprint to desflurane use, which reflects the differing amounts used (56,000L vs 21,000L respectively).  

Discussion 

This is the first paper to look at the carbon footprint of IAG manufacture. This makes a 5-fold difference in the life-cycle carbon footprint of sevoflurane.

The use of vapour capture technology can reduce the carbon footprint of IAGs, potentially to a level comparable with a propofol-based anaesthetic. However, if the manufacture of propofol is with renewable energy, its carbon footprint could be further reduced, potentially below that of IAGs with vapour capture.

Further work should identify and expand on concerns over propofol’s environmental impact beyond its carbon footprint, and then weigh those against the impact of the IAGs. 

The study assumes a volume of anaesthetic gas will be captured by VCT and recycled only once, but it is likely that gases can be recycled more than once, thus the paper could underestimate the environmental benefits of using VCT. 

Conclusion

This paper demonstrates the impact of different manufacturing methods on the carbon footprint of anaesthetic gases. It has shown that using low flow oxygen/air mix with anaesthetic gases lowers their carbon footprint and this can be reduced further with vapour capture technology. Propofol-based anaesthesia has the smallest carbon footprint.

Sevoflurane has the lowest carbon footprint of the IAGs, but only if manufactured in a certain way. The proportion of sevoflurane manufactured in this way is not yet clear and this question could form the basis of further collaboration with industry.

Further studies could look at the potential to recycle gases multiple times and how that impacts on overall emissions, so sustainable pathways can be further developed in the pursuit of delivering a ‘net zero’ anaesthetic. 

Chris Allen

Association of Anaesthetists and Centre for Sustainable Healthcare Fellow in Environmentally Sustainable Anaesthesia
Newcastle upon Tyne Hospitals

April 2021