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Lambeth Climate Partnership
KCH Anaesthetics Team
Waste, consumption & food

Anaesthetic Gas Waste: Reducing the carbon footprint of nitrous oxide in hospitals

Organisation
King's College Hospital

Theme
Waste, consumption & food

Start Date
Apr 2022

End Date
Apr 2024

Goals
Consumption, Waste

Analysis of the use of nitrous oxide at King’s College Hospital in Denmark Hill revealed huge amounts of waste from their piped systems.

KCH saved over 3,000 tonnes of CO2e and £20,000 by decommissioning unused piped systems and switching to much more efficient portable cylinders across wards and clinics. 

The Challenge

One of the biggest contributors to the NHS's carbon footprint is medicines, accounting for 25% of the total footprint. Nitrous oxide currently has the largest carbon footprint of the anaesthetic gases within the sector, accounting for at least 75% of the total anaesthetic gas footprint.

While other volatile anaesthetic agents are known to be environmentally harmful, nitrous oxide is a big problem due to its frequent use, particularly in dental and paediatric procedures.

As part of the Trust’s Green Plan (opens in a new window), King's College Hospital committed to reducing the carbon footprint of nitrous oxide by tackling waste through leaks in the piped systems, theft and over-ordering of gas cylinders.

Staff realised that moving away from large manifolds (clusters of cylinders that supply piped gas to wards) where nitrous oxide gas is piped all around the hospital to smaller, portable cylinders on the anaesthetic machines would provide a leaner, more efficient supply. Large piped systems are known to leak, and overcoming this can lead to huge carbon, cost and resource savings.

95%

of Nitrous Oxide gas was not used per year. 

Action Taken

Staff at King’s found they could massively reduce the amount of waste nitrous oxide used across the hospitals by replacing larger delivery manifolds with more efficient portable gas cylinders in clinical areas. King’s College Hospital is one of the first Trusts in the country to decommission all nitrous oxide manifolds, saving over 100,000 litres of nitrous oxide waste in the process.

As part of the trial, they carried out a clinical audit across all clinical areas served by piped nitrous oxide and found that, on average, 1,605 litres were used weekly, or 83,460 litres per year. They then compared this to the amount the Trust bought per year, 915,000 litres. These stark figures showed that only 5% of the gas bought was used clinically, so 95% was wasted.

By defining this waste, staff at King’s College Hospital concluded that the main source of leaks was through the manifolds. There is a growing understanding that clinical usage is almost always low enough to be supplied via local cylinders, drastically reducing wastage. 

Carbon emissions and wastage were hugely reduced thanks to the decommissioning of piped supply from areas with little to no clinical usage and converting anaesthetic gas machines to portable cylinders in all other areas that still needed nitrous oxide.

By converting to small portable cylinders, they are able to provide a leaner supply without changing patient care or experience.

The Results

King’s is one of the first Trusts in the country to decommission all of its nitrous oxide manifolds. By decommissioning these outdated manifold systems and providing more efficient supplies of nitrous gases at King’s College Hospital, we have saved around 350 people’s worth of carbon emissions per year.

Nitrous oxide's carbon footprint in 2021 was 4,500 tCO2e (the equivalent of burning two million kg of coal). Since then, we have saved 3,421 tCO2e by reducing nitrous oxide waste.

While the gas is cheap, manifold maintenance is not. A manifold-free supply allows for cost savings of £20,000 a year. This switch will help the hospital reduce its nitrous oxide footprint to less than 100 tonnes CO2e annually.

These changes can be undertaken in every hospital to reduce the carbon footprint of anaesthetic gases, mitigating climate change and reducing air pollution. This work will have an impact for years to come - it protects our staff and patients and hugely reduces our carbon emissions, helping protect our planet.

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