Intended for healthcare professionals

Practice Sustainable Practice

Sustainable practice: Cutting nitrous oxide loss and waste

BMJ 2023; 383 doi: (Published 06 November 2023) Cite this as: BMJ 2023;383:e076649

Linked Editorial

Sustainable practice: what can I do?

  1. Rebecca Taylor-Smith, anaesthetic registrar1,
  2. Sophia Lentzos, head of sustainability2,
  3. Richard Seglenieks, consultant anaesthetist3
  1. 1Department of Anaesthesia, Worcestershire Royal Hospital, UK
  2. 2NIHR Evaluation Trials and Studies Coordinating Centre, UK
  3. 3Department of Anaesthesia, Pain and Perioperative Medicine, Department of Critical Care, Footscray Hospital, University of Melbourne, Australia
  1. Correspondence to R Taylor-Smith rebecca.taylor-smith{at}

What you need to know

  • Nitrous oxide (N2O) is a greenhouse gas—one of six critical gases targeted for reduction in the Kyoto Protocol

  • Waste reviews can reduce consumption of N2O considerably—in some cases by up to 98%

  • Clinicians have an essential leadership role in initiating and contributing to waste reviews to minimise N2O waste

Nitrous oxide (N2O) is a greenhouse gas and ozone depleting drug that is commonly used in hospitals worldwide. A high proportion of the drug is lost or wasted, contributing to unnecessary greenhouse gas emissions. Emissions of N2O can be reduced by cutting use or catalytic cracking; here we outline the methods to reduce emissions from piped N2O waste.

Why change is needed

N2O is used as an inhalational anaesthetic agent or mixed with oxygen and air (mixed N2O) for pain relief in labour wards, emergency departments, and pre-hospital environments. It is a potent greenhouse gas—one of six critical gases targeted for reduction in the Kyoto Protocol1—that has a 100 year global warming potential almost 300 times that of carbon dioxide (CO2), and is an ozone depleting substance, lasting 114 years in the atmosphere.234 It is also hazardous, and reducing exposure brings occupational health advantages.5

N2O is typically supplied in hospitals through manifolds, which comprise banks of cylinders that supply piped N2O throughout the hospital to outlets that connect to anaesthetic machines (fig 1). Mechanisms of loss and waste of piped N2O include:

  • Poor stock rotation resulting in unused cylinders being returned to the manufacturer

  • Over ordering of N2O stock resulting in expired cylinders being returned to the manufacturer and vented to the atmosphere

  • Leaking outlets or pipework

  • Theft—N2O has a street value and is at risk of theft if not tracked and secured adequately.

Mixed N2O can be supplied by manifolds to wall outlets or gas blenders for procedural sedation or labour analgesia. Similar principles can be applied to reduce loss of mixed N2O.

Fig 1
Fig 1

Schematic of manifold supplying N2O

Evidence for the solution

Research carried out across 16 sites in Scotland in 2019/20 identified waste of N2O averaging 95% resulting from several of the above mechanisms of waste and loss.5 This led to the creation of the Nitrous Oxide Project which recommends a multidisciplinary approach to efficiently and systematically identify system waste and improve medical gas management 6 In NHS Lothian, this approach allowed one hospital to reduce consumption of piped N2O by 98%.

Similar levels of waste and loss have been shown in several countries.5678 A letter published in the British Journal of Anaesthesia highlighted a discrepancy between clinical use and procurement of N2O cylinders in Australia equivalent to the CO2 emissions of driving 600 000 km in a passenger car and a financial cost of more than 2000 Australian dollars (£1041, €1204) annually. The loss in this case was attributed to a leaking N2O outlet.3

What you can do

A waste review is a review of how N2O is used throughout the hospital. It is a multidisciplinary process involving clinicians who use N2O, pharmacists, and estates and facilities teams. In the UK waste reviews are typically overseen and initiated by a medical gas committee but we would encourage any member of staff with an interest in sustainability to contact their medical gas committee to ask what steps have been taken so far to consider N2O waste and loss. Clinician support is crucial to help the committee with this work as clinicians are best placed to communicate clinical need and current use of N2O. Table 1 outlines the steps for how a waste review might lead to significant reductions in N2O waste, based on the Nitrous Oxide Project methodology5 and our experience. Outcomes from a waste review may include:

Table 1

Fictional example of a waste review.
Dr Green works in a general hospital with eight operating theatres and is concerned about N2O waste

View this table:
  • Ensuring that pharmacy ordering schedules align with clinical use to avoid waste of expired cylinders

  • Ensuring adequate security of N2O cylinders

  • Ensuring regular checks and maintenance of manifolds to minimise system loss and capping off piping when it is no longer in use

  • Opting for individual cylinders at the point of use instead of manifold supply. In this scenario, optimise the number of individual cylinders to reduce waste9

  • Stopping use of N2O. Many hospitals have taken this step. Agreement to stop using N2O will depend on local case mix and clinician agreement. This process will take time as it involves multiple departments and governance processes. We recommend pursuing efforts to minimise waste in the meantime, even if decommissioning manifolds is being planned.

Education into practice

  • Whom could you contact in your hospital to find out more about whether there is scope to reduce N2O waste in your workplace?

  • How would you engage clinicians to discuss current usage and clinical need for piped N2O in your hospital?