A London hospital has slashed waste of nitrous oxide from almost total loss to just 5%, in a project that could help the NHS significantly reduce its environmental impact.
The initiative at St Bartholomew’s Hospital, part of Barts Health NHS Trust, targeted the use of nitrous oxide, a powerful greenhouse gas (aka ‘laughing gas’) which is widely used in anaesthesia but has a global warming impact far greater than carbon dioxide.
In 2023, Barts Health was the highest user of nitrous oxide per operation in the UK, generating 44kg of CO₂ per procedure compared with a national average of 17kg. Investigations revealed that as much as 98.5% of the gas supplied to St Bartholomew’s was being lost, largely due to leakage from its piped delivery system.
In response, a specialist project team analysed the gap between gas purchased and that used clinically, identifying significant inefficiencies. The hospital then moved away from its central piped system – previously fed by large external cylinders – to a more targeted approach focused only on areas where nitrous oxide was essential.
Following a successful pilot, which confirmed there were no impacts on safety or performance, the system was fully decommissioned. By March 2025, operating theatres and catheter labs had switched over, wall-mounted ports were sealed, and external cylinders removed.
The changes were supported by £15,000 in funding from NHS England and are expected to deliver ongoing annual savings of £11,000, alongside a dramatic reduction in emissions.
The project comes as growing evidence highlights the environmental cost of nitrous oxide use across healthcare. Recent research from University College London found the gas is a significant contributor to emissions in dentistry, where it is commonly used to treat anxious patients.
The study showed that nitrous oxide has a global warming potential 273 times greater than carbon dioxide, with each dental sedation appointment producing an average of 28.6kg of CO₂ equivalent – roughly the same as driving more than 70 miles in a petrol car.
Crucially, the research also found that systems using centrally piped gas – like the one previously in place at St Bartholomew’s – had around 30% higher wastage than those using individual cylinders, reinforcing the findings from the hospital’s own investigation.
At St Bartholomew’s, clinicians worked closely with estates teams, engineers and safety specialists to ensure the transition maintained clinical standards while reducing environmental harm.
The success of the project is likely to inform similar efforts across the NHS, as the health service works towards its net zero targets and looks to reduce reliance on high-emission anaesthetic gases.
Experts say the combination of real-world interventions and emerging research evidence strengthens the case for rethinking how nitrous oxide is delivered and used across healthcare settings.
Andrew Wragg, medical director at St Bartholomew’s, said: ‘This achievement highlights the power of clinical leadership and collaboration to deliver meaningful environmental change, improving sustainability, reducing costs, and maintaining the highest standards of patient care.
‘St Bartholomew’s was the first hospital to complete the switch-off, with Whipps Cross and Newham hospitals following closely behind. The Royal London Hospital is currently working towards a complete switch-off.’
Henna Roberts, senior change manager, added: ‘The nitrous oxide project is part of ongoing efforts to deliver on our green objectives. If you have any ideas or are delivering green projects you’d like to share, please do get in touch.’
Photo: MM Dental
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