Sustainable practice: Cutting nitrous oxide loss and 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

Schematic of manifold supplying N₂O

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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:

• 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.