Conservative low-flow anaesthetic techniques could lead to reduced carbon footprint for veterinary practices

4 June 2021

Oxygen and inhaled anaesthetic agent consumption could be significantly reduced if anaesthetic procedures were audited and adapted, found a new study, published in the Journal of Small Animal Practice (JSAP). This in turn could lead to reduced greenhouse gas emissions and financial expenditure.

The study “Sustainable veterinary anaesthesia: single centre audit of oxygen and inhaled anaesthetic consumption and comparisons to a hypothetical model”, retrospectively reviewed the records of 100 consecutive anaesthetics from a typical week at the Queen Mother Hospital for Small Animals, Royal Veterinary College, UK. Cases were included if the anaesthetic had an accompanying record that contained the animals’ bodyweight and all the 5-minute recordings of fresh gas flows and vaporiser settings for the duration of the anaesthetic. The volume of oxygen and inhaled anaesthetic agent (IAA) used per 5-minute period were calculated based on the records. The carbon footprint through greenhouse gas emissions was calculated in carbon dioxide equivalents (CO2e).

Each anaesthetic was then reassessed to establish whether any reductions in oxygen flows could be made by utilising a conservative low-flow technique. In addition, desflurane was swapped, where there was not a clear benefit to its use, for an equipotent dose of sevoflurane. Animals with bodyweights over 5 kg were assigned to circle systems set at a maintenance flow of 1 L/min following a short transitional period of higher flow. Animals with bodyweights less than 5 kg were assigned to Mapleson-A breathing systems at a flow of 1 L/min.

Potential reductions in oxygen and inhaled anaesthetic agent consumption and CO2e were calculated. A total of 43,132l of oxygen (6.3 J size cylinders) were used to vaporise 2605ml of liquid sevoflurane (10.4x250ml bottles), 1596ml of liquid isoflurane (6.4x250ml bottles) and 22ml of liquid desflurane (0.1x240ml bottles). Hypothetical oxygen consumption was 16,798l (2.5 J size cylinders), representing a reduction of 61%. This would have lowered IAA consumption to 112ml of liquid sevoflurane (4.5x250ml bottles; a 57% reduction) and 589ml of liquid isoflurane (2.4x250ml bottles; a 63% reduction). It was assumed that desflurane was not clinically necessary and that it was exchanged for an equipotent volume of sevoflurane in the analysis.

The estimated CO2e calculated for actual IAA consumption was 1.81 metric tonnes of CO2e. Sevoflurane contributed 0.51 metric tonnes (28%), isoflurane 1.19 metric tonnes (67.2%) and desflurane 0.08 metric tonnes (4.5%) of CO2e. This could have been lowered to 0.67 metric tonnes using the hypothetical low flow techniques, representing a reduction of 63%.

Matt McMillan, corresponding author for the paper, said: “We often don’t think of the environmental impact of veterinary practice, but it can be extremely wasteful. Just like in every other aspect of modern life, we have a duty to reduce emissions of greenhouse gases to help slow climate change.”

“All inhaled anaesthetic agents are greenhouse gases and by reducing the fresh gas flows we use as much as possible, through the utilisation of rebreathing systems, we can reduce the amount of them released into the atmosphere. Ultra-low flow anaesthesia may not be achievable in many situations but this study demonstrates that, by adopting a simple conservative-low flow anaesthetic technique, practices which routinely use non-rebreathing systems should be able to significantly reduce the carbon footprint of anaesthesia. Obviously this is only one small part of a practice’s environmental impact but it is a proportion that can be readily reduced in an effective, safe and practicable fashion.”

Nicola Di Girolamo, Editor of JSAP, concluded: “As veterinary professionals, we recognise the importance of protecting the environment and doing what we can to reduce our carbon footprint. This study was a good first step towards understanding the potential reductions in IAA consumption that can be made in veterinary practice. The methodology for this study was justifiable in light of the COVID-19 pandemic, allowing for rapid data collection and analysis in a short time-period. Future research should include a prospective clinical trial or a full clinical audit.”

An early online version of the article has been published here. It is open access and can be freely accessed by anyone.

The Journal of Small Animal Practice is published monthly and access to articles is free for BSAVA members. For information on how to become a BSAVA member visit

1M. McMillan (2021) Sustainable veterinary anaesthesia: single centre audit of oxygen and inhaled anaesthetic consumption and comparisons to a hypothetical model. Journal of Small Animal Practice, 62 (6). Available at: