Nitrous Oxide (N2O) is a major contributor to anthropogenic climate change.1 It is a known potent greenhouse gas and ozone depleter which is used within the healthcare system as an analgesic and sedative agent.2 Clinical use is mainly via Anaesthetists in the operating theatre and on the labour ward for pain relief for labouring mothers.
The aim of the Kn2oW Nitrous Campaign is to increase awareness around the detrimental environmental impacts Nitrous Oxide and to help provide guidance on reducing health care emissions of this greenhouse gas. Click on the links below to find out more information on this issue.
Environmental Impact of Nitrous
Nitrous Oxide (N2O) is a greenhouse gas with a 100 year Global Warming Potential 273 times that of carbon dioxide.1 This is primarily due to a long atmospheric lifetime. N2O lingers in the atmosphere for 110 years allowing it to move up into the stratosphere where it has ozone depleting effects.3 Therefore N2O used today for a paediatric induction will likely still be in the atmosphere for the entirety of that childs lifetime.
A recent Intergovernmental Panel on Climate Change report states that net zero CO2 emissions are required by the early 2050’s to limit global warming to a somewhat manageable 1.5 degrees.1 This means that reducing our carbon emissions has never been more important. The healthcare sector in Australia accounts for 7% of the total national carbon footprint.4 N2O is estimated to be roughly 2-3% of the National Health Service (NHS) emissions in the UK.5,6 Therefore assuming similar N2O use in Australia it is a significant single agent contributor to climate change. As one of the primary users of N2O in the health care setting Anaesthetists are in a prime position to drive change in this area.
Evidence for clinical nitrous oxide use.
Nitrous oxide is one of the earliest anaesthetic agents to be discovered with its first clinical use by dentists in 1844.2 It provides both sedation and analgesia and has a rapid onset and offset which has led to its ongoing use into the 21st century. However, the development of newer anaesthetic agents and better understanding of climate science has an increasing number of Anaesthetists questioning the role of N2O in modern anaesthesia.
In Western countries use of nitrous oxide in anaesthesia is declining.7 The discovery of new anaesthetic drugs with rapid onset and offset pharmacokinetics and fast acting opioids has removed the clinical need for Nitrous Oxide. Audit of the Sir Charles Gairdner Hospital consultant body found minimal clinical use of Nitrous Oxide at this adult only hospital. Common situations in which it is still used within anaesthesia include as part of a paediatric gas induction and in GA caesarean sections to limit uterine atony from sevoflurane. As Total Intravenous Anaesthesia (TIVA) becomes a more common anaesthetic approach in these two patient groups the clinical use of Nitrous oxide will be further diminished.
The major clinical use of nitrous oxide is not in theatres but on the labour and birth suite. Nitrous oxide is used in labour as an analgesic despite having poor evidence for its efficacy.8 It has been shown to provide small improvements in pain scores when compared with placebo at the expense of higher rates of nausea, vomiting and dizziness.8 It has been shown to be less efficacious then epidural and Remifentnail PCA. Reducing emissions in this area is difficult but several strategies have been proposed. Antenatal education of mothers to help them make informed decisions about labour analgesia and earlier epidural or PCA may both reduce nitrous oxide use. Nitrous oxide destruction systems have been introduced in Sweden and have helped them reduce their labour nitrous oxide use by 50%.8 Limiting the clinical use and wastage of nitrous oxide along with safe destruction of this gas provide means by which emissions of Nitrous Oxide can be reduced.
Leaks are a major source of N2O emissions
Leaks in ageing N2O manifold and pipeline infrastructure results in significant wastage of N2O into the atmosphere. The UK Nitrous Oxide Project, led by pharmacist Alifia Chakera, found that wastage via leaks accounted for over 95% of the N2O use in 16 NHS hospitals that were audited.9,10 Data from other hospitals in Ireland, NZ and Australia show that the issue of wastage due to leak is likely to be a common problem.11,12
Sir Charles Gairdner Hospital (SCGH), an adult only hospital in Perth, performed a clinical audit comparing N2O purchasing with estimates of clinical use. They found that they were purchasing over 90% more N2O then they were clinically using and subsequently a leak in the manifold regulator was found and fixed. At SCGH there was no service contract in place to regularly assess for leaks and it was unclear when this had last happened.
After six months of decreased N2O purchasing a sudden uptick suggested the occurrence of a new leak. Following the maintenance guidelines of the Australian Standards the search for the leak involved visual inspection and soapy water testing of key parts of the system. This failed to identify the problem. Further examination of the system by pressure testing confirmed the presence of a leak. When focused pressure testing of individual limbs and theatre piping occurred, not one but five leaks were found. There was a large new leak in a worn copper pipe and there were leaks in four theatre pendant systems. These pendant leaks were likely to have been long term and missed with previous visual testing strategies. SCGH has now disconnected from the piped nitrous supply and are moving towards decommissioning the entire system and manifold.
An application has been made to the Australian Standards to add pressure testing to the standard regime. Below is a protocol for pressure testing devised by the team at Fiona Stanley Fremantle Hospital Group.
Check out our protocol for testing your hospital’s nitrous pipeline for a leak
Kn2oW Nitrous Steps to Reduce Emissions
Climate change is a problem for us all to tackle. As the guardians of inhaled anaesthetics Anaesthetists have a major role to play in reducing health system emissions due to N2O. The Kn2oW Nitrous campaign hopes to empower people to take a closer look at N2O consumption in their hospital with the aim of reducing carbon emissions. To make things easier we have provided some simple steps to follow for anyone interested in tackling this issue in their own institution. Just contact the relevant person within your hospital and follow the steps provided
N2O Pipeline Map
- Ensure the map of N2O infrastructure is up to date and decommission any unused outlets or limbs. This will decrease the risk of leak from unnecessary piping.
- Ensure that your hospital has a service contract to regularly assess piping infrastructure for leaks. Find out who does the checks and how frequently. In addition to following the Australian Standard, the system should be pressure tested.
- Ascertain the size of the N2O manifold. If decommissioning is not possible consider downsizing the manifold so regular purchasing is needed. This decreases the cost of cylinder hire and enhances the detection of new leaks.
Finance or Gas Provider
- Determine the timing and amount of N2O procured by your hospital over the last 5 years.
Clinical Use Audit
- Audit the clinical use of N2O within the department by consultant survey and interrogation of the anaesthetic machines. Determine if clinical use matches purchasing. Click here to go to our clinical audit page for more information.
- Provide an education session for your department. Discuss the environmental impacts of N2O, findings of the clinical audit and potential strategies to reduce N2O use.
- Consider decommissioning the piped N2O system in adult only hospitals. Provide small portable cylinders to selected anaesthetic machines and portable entonox cylinders to be used as required.
Nitrous Oxide Clinical Use Audit
A departmental audit of clinical use of N2O can be helpful on multiple fronts. It allows comparison between procurement and clinical use, with any discrepancies helping identify leaks within the N2O infrastructure. It also allows for understanding of N2O clinical use patterns within the department to help focus interventions to help reduce clinical use of N2O. At SCGH we used both a clinical use survey and anaesthetic machine interrogation to get the required data. We received the procurement data from our local gas provider which in WA is BOC gas. Below are links to our generic survey and machine interrogation information.
Click here to go to Machine Interrogation information
Click here to go to Generic Clinical Use Survey information.
1. Climate change 2021: The physical science basis. [internet]. New York (USA): Intergovernmental Panel on Climate Change; 2021 [cited 2023 Feb 14]. Available from: https://www.ipcc.ch/report/ar6/wg1/
2. Buhre et al. European Society of Anaesthesiology Task Force on Nitrous Oxide: a narrative review of its role in clinical practice. BJA. 2019; 122(5): 587-604.
3. Campbell M, Pierce T. Atmospheric science, anaesthesia and the environment. BJA Education. 2015; 15(4): 173-179.
4. Malik et al. The carbon footprint of Australia health care. Lancet Planet Health. 2018; 2: 27-35.
5. Baddley J. Is green the new blue? 2019 [cited 11 July 2022]. Available from: https://www.youtube.com/watch?v1⁄4x5yl7nZsApQ.
6. Faculty of Public Health Special Interest Group: Sustainable Development. The NHS carbon footprint [internet] 2018 [cited 11 July 2022]. Available from: https://www.fph.org.uk/media/3126/k9-fph-sig-nhs-carbon-footprint-final.pdf
7. Brown S, Sneyd J. Nitrous oxide in modern anaesthetic practice. BJA Education. 2016; 16(3): 87-91.
8. Riley et al. Australasian Anaesthesia. ANZCA. 2021 [cited 10 Dec 2022]. Available from : https://www.anzca.edu.au/resources/college-publications/australasian-anaesthesia-(the-blue-book)/blue-book-2021.pdf
9. Spencer N et al. NHS Lothian nitrous mitigation project: assessing nitrous oxide usage at a district general hospital. Anaesthesia. 2021; 76(6): 24.
10. Wise J. Creating more sustainable practice: the NHS clinical teams innovating for a greener future. BMJ. 2021; 375: 1-3.
11. Seglenieks R et al. Discrepancy between procurement and clinical use of nitrous oxide: waste not, want not. BJA. 2022; 128(1): 32-34.
12. Keady T et al. Annual greenhouse gas emissions from inhaled anaesthetic agents in the Republic of Ireland. BJA. 2023; 130(1): 13-16.