The No 2 N2O Project

Nitrous oxide (N₂O) used in healthcare settings is responsible for 75% of the world’s anaesthetic gas carbon footprint, and is used in many hospital departments including operating theatres, labour wards, dental clinics and emergency departments.¹ Northern Sydney Local Health District (NSLHD) is working to limit the use of N₂O to support its target of net zero emissions by 2035.

N₂O accounts for 3% of global carbon dioxide (CO₂) equivalent emissions and is an extremely potent greenhouse gas due to its high global warming potential and its endurance in the atmosphere, taking over 100 years to break down.^2.3  

To combat the impact of N₂O, the NSW Ministry of Health has established a key performance indicator for local health districts to reduce emissions attributed to N₂O by 5% each year. Studies conducted in both Australia and overseas have determined more than 70% of N₂O emissions in healthcare settings are from leaks in piping and outlet infrastructure rather than clinical use.⁴

This has led to the following recommendations:

• avoiding piped N₂O in new hospital builds where clinical use is limited
• regular maintenance and pressure testing of current N₂O infrastructure
• abandoning underused and ageing existing pipe systems
• using small, portable e-cylinder tanks as a substitute where appropriate.

Reducing carbon emissions in our hospitals

Staff education has been employed to shift attitudes and usage behaviours, and work is underway to decommission unused N₂O piped infrastructure, as well as identify and repair leaks in pipe and outlet infrastructure.

The project team took a baseline measurement of N₂O usage in Royal North Shore Hospital (RNSH) operating theatres, revealing that RNSH uses 16,000L of N₂O in a two-month period. This is the equivalent of driving a petrol car 47,887km (8,533kgCO₂e).⁵

The team surveyed staff at RNSH and Hornsby Ku-ring-gai Hospital anaesthetic departments on their attitudes, beliefs and behaviours in relation to N₂O, as part of a prospective cohort study led by Royal Prince Alfred Hospital. Provisional results from this survey (58% response rate) showed that 84% of anaesthetists and trainees had used N₂O in their practice over the last 12 months, and of these, 60% were actively trying to reduce their N₂O use. The study also demonstrated that although anaesthetists wish to continue to use N ₂O in some capacity, they are accepting of N₂O supply by cylinder.

Extensive staff education followed this survey to further increase awareness of N₂O’s high global warming potential and highlight the LHD’s commitment to an annual reduction in N₂O use and real-time actions staff can take to reduce their usage.

The project team presented to anaesthetic departments across all NSLHD’s hospitals as well as some local private hospitals, and supporting educational posters were displayed within operating theatres. Progress has been made regarding piped infrastructure across the LHD, with one building at RNSH identified for decommissioning and replacement with N₂O cylinders following consultation with affected clinical areas. The hospital executive team are currently considering this for approval.

Exploring potential to install a N₂O flow meter

The next stage of the project involves testing used N₂O pipe infrastructure to identify any leaks into the surrounding environment. Current best practice techniques involve pressure testing of pipes and submersion of joints in soap and water, however much of this infrastructure pathway is within walls and roofs, making it inaccessible. Real-time monitoring using a flow meter which attaches to piping may be an alternate solution.

The Children’s Hospital at Westmead has installed a first-of-its-kind N₂O flow meter to determine the presence and quantity of N₂O leakage from its pipes. RNSH is also exploring this option. Participating in a statewide NSW Health N₂O Working Group, established in 2022, has allowed collaboration with like-minded clinicians and other health agencies, including Health Infrastructure NSW, which has been essential for local progress.

This project was part of the NSLHD Net Zero Leads Program.

References

1. National Atmospheric Emissions Inventory. UK Greenhouse Gas Inventory Annual Report 1990 to 2011. United Kingdom; 2013. [cited Jul 2024].
2. McGain F, Muret J, Lawson C, Sherman JD. Environmental sustainability in anaesthesia and critical care. Br J Anaesth. 2020;125(5):680-692. doi:10.1016/j.bja.2020.06.055
3. Sulbaek Andersen MP, Nielsen OJ, Wallington TJ, Karpichev B, Sander SP. Medical intelligence article: assessing the impact on global climate from general anesthetic gases. Anesth Analg. 2012;114(5):1081-1085. doi:10.1213/ANE.0b013e31824d6150
4. Devlin-Hegedus J. A., et al. Action guidance for addressing pollution from inhalational anaesthetics, 2022, Anaesthesia Perioperative medicine, critical care and pain, 77(9), p.1023-1029, doi: https://doi.org/10.1111/anae.15785
5. GOV.UK. Greenhouse gas reporting: conversion factors 2023. United Kingdom; 2023. [cited Jul 2024].