Organisation: East Lancashire Teaching Hospital NHS Foundation Trust (ELHT)

What was the issue?

NHS England is estimated to contribute 4-5% of the country’s total carbon footprint. The NHS has set targets of achieving net zero emissions by 2040 with an 80% reduction in carbon footprint by 2028.  It is estimated that anaesthetic gases contribute to 5% of the total NHS carbon footprint.

Nitrous oxide (N₂O) is a medical gas that has been part of anaesthetic use since its discovery in 1772. Although its widespread use has mostly been superseded in modern practice with the availability of superior pharmacological agents, it is still used commonly in anaesthetic practice.

The use of N₂O comes with a significant environmental cost. The global warming potential (GWP) of N₂O is 310x that of CO₂ with a physical atmospheric presence of 150 years. As such, the use of N₂O represents a relatively large proportion of both anaesthetic and NHS CO₂ footprints.

The Nitrous oxide mitigation project in NHS Lothian identified that trust usage of N₂O can be significantly reduced without impacting clinical practice. The project found that leaks within the often very old, manifold systems can contribute massively to trust N₂O usage and subsequent CO₂ footprints.

What action was taken?

The Nitrous Oxide Mitigation Project was launched in 2021 by Alifia Chakera in NHS Lothian, Scotland. This project recognises the declining use of N₂O in routine anaesthetic practice and its significant environmental impact.

The project identified waste via significant leakages in the N₂O storage systems at multiple trusts covering NHS Scotland. At Lothian a significant pipeline leak was demonstrated resulting in the decommissioning of the N₂O manifold reducing N₂O consumption by 98% for the same clinical use.

At ELHT, we aimed to replicate the nitrous oxide mitigation project with the following specific aims:

1. Evaluate the size and suitability of the nitrous oxide manifold to current clinical requirements at ELHT.
2. Evaluate our environmental impact in relation to N₂O use.
3. Identify areas of waste i.e. leakage in the storage and distribution infrastructure.
4. Emphasise growing need for dedicated commitment to environmental sustainability going forward as a department.

Our nitrous oxide use was evaluated via the following methods:

1. Review of manifold designs and logbooks at each ELHT site
2. Review current anaesthetic usage by assessment of anaesthetic machine logbooks
3. Survey of ELHT anaesthetists to review current practice regarding N₂O use.

What was the Delivering a Net Zero NHS benefit? 

At the Blackburn site we found extremely high manifold N₂O turnover of 8,262,000L in 2 years, equating to 5,031 tonnes in CO₂e. In comparison, anaesthetic machine usage data produced an extrapolated yearly usage of approx. 11,000L. Clinical use is 0.26% of manifold turnover. The pipeline was formally tested and demonstrated a large leak. In Q2 2021 the pipeline was isolated and decommissioned as repair was deemed to be unjustifiable.

At the Burnley (BGH) site we found high manifold N₂O turnover of 198,000L in 1 year equating to 121 tonnes of CO₂e. In comparison, anaesthetic machine usage data produced an extrapolated yearly usage of approx. 42,960L. Clinical use is 21.6% of manifold turnover.

The pipeline at BGH has been decommissioned as of 18/05/22.

N₂O remains available at both sites via directly attached machine cylinders.

The N₂O leak at Blackburn is an enormous environmental and financial burden to the tune of £12,500 and an estimated CO₂e of 2,515 tonnes per annum. A 10-year extrapolation equates to £126,000 & 26,000 tonnes of CO₂e.               

Size E portable N₂O cylinders are estimated to cost the trust £87 and generate a CO₂e of approximately 7.6 tonnes per annum if fully discharged.

Link for further information:

Link to more detailed case study and Powerpoint presentation.

Key contact and email: Dr Jason Lie (Consultant Anaesthetist and Sustainability Lead ELHT) – jason.lie@elht.nhs.uk