All anaesthetic gases are greenhouse gases. Their greenhouse warming potential is expressed as GWP100 (that is the heat absorbed by a unit mass of gas in comparison to the same mass of CO2 over a 100-year lifespan). This is very much dependent on the persistence of the compound in the atmosphere.
Sevoflurane and desflurane are hydroflurocarbons (HFCs), otherwise known as F-gases. The use of HFCs as an alternative to CFCs has proliferated in multiple industries since the Montreal Protocol in 1987 to protect the ozone layer. The C-F bond is particularly stable, and hence hard to break down. This makes modern anaesthetic gases much less flammable compared to predecessors. The downside to this is they persist in the atmosphere and contribute to global warming.
Nitrous oxide (N2O) has similar properties but also breaks down ozone (O3) by reacting with it to form nitrogen and oxygen1. Use of nitrous oxide as an adjunct in general anaesthesia has decreased over the years due to its multiple side effect profile, but it is still frequently used by birthing moms during labour.
There has been a lot of attention on desflurane in recent years within the field of anaesthesia, due to its environmental effects, when there are alternatives in the form of sevoflurane and TIVA (total intravenous anaesthetic). Desflurane provides a quicker wake-up profile compared to sevoflurane (3-8 minutes)4, but this difference can be reduced or made negligible by titrating down sevoflurane and TIVA towards the end of surgery.
Within our institution, desflurane is 2.6x more expensive than sevoflurane by volume, and because 3x more is needed to keep patients asleep, in clinical practice, it can be 8x more expensive, although savings tend to be lesser due to lower flows. The use of TIVA is associated with one-third the emissions of sevoflurane per hour of anaesthetic5. TIVA, however is associated with increased solid waste generation and leakage of the drug, propofol, has a high bioaccumulation potential and can be toxic to aquatic life.
How did we reduce it?
We initiated a quality improvement project in 2021 to reduce the usage of desflurane6. This included surveying clinicians’ motivations for using it. Reasons varied from a lack of knowledge about its environmental effects to familiarity and ease of use with the agent.
We tackled the issue through a series of multi-faceted approaches. This included education, raising awareness, and organising talks from international speakers to show that other countries were already forging ahead in this regard. Other interventions included familiarising clinicians with sevoflurane and TIVA, as well as, pasting stickers on anaesthetic machines to remind users of the cost and environmental implications. We also promoted the use low-flows during general anaesthesia, or alternatively, consider regional anaesthesia. Whilst the full extent of intervention strategies go beyond the scope of this article, it is important to build a green culture that not only focuses on desflurane. This culminated in our “Greening the OT” movement, which targeted other areas such as waste segregation and reduction, rationalisation of oxygen, drugs, etc. The movement is now part of the bigger NUHS Sustainability drive towards net zero by 2045.
You can read more about our QIP here: Developing a quality improvement project to tackle the desflurane problem. KS Ang et al. BMJ Open 2023
Between the period of April 2021 and March 2023, our usage of desflurane has reduced by 90%. This has saved us S$577,192 and 1,904 tonnes of CO2e over the past 24 months even after accounting for the increase in TIVA usage. This is the equivalent of taking 340 cars off the road per annum. This demonstrates that environmental sustainability and cost savings can go hand in hand, reinforcing the triple bottom line approach.
NHS Scotland has announced an immediate ban on desflurane in March 20237, and NHS England will follow suit in 20248. The EU has proposed a ban on HFCs, including desflurane, from 2026 onwards9. Many hospitals around the world have removed desflurane from their formulary. Other institutions around Singapore have made similar moves to reduce their desflurane usage.
Besides this, we have begun to engage with the NUS School of Engineering to develop vapour capture technology, which is still in its infancy, even overseas. The captured gases may then be processed for reuse again, but this will be dependent on HSA approval. Our department is also in touch with a Swedish company to trial the use of nitrous oxide cracking units in labour ward to catalyse these gases into inert compounds before release into the atmosphere. We have also removed spare N2O cylinders off the back of our anaesthetic machines. More importantly is the need to decommission N2O pipelines, which has been done in AH. The savings are tremendous as well.
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