Anaesthetic gases calculator | Association of Anaesthetists
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Anaesthetic gases calculator

Anaesthetic gases calculator

Inhalation anaesthetics, such as nitrous oxide, isoflurane, desflurane, and sevoflurane contribute to climate change.

Dr Tom Pierce has created a CO2e and cost calculator, which compares both the financial cost and carbon dioxide equivalence (CO2e) of inhalation anaesthesia.

Download the anaesthetic gases calculator

What assumptions have been made?

The global warming potential (GWP) of the inhalational anaesthetic agents have been taken as:

  • Nitrous oxide:  310
  • Isoflurane: 510
  • Sevoflurane: 130
  • Desflurane:  2540

The unit cost of each bottle of inhalational agent can be changed according to local pricing.

The current cost of nitrous oxide is 0.23 p/ litre, but this is from a size E cylinder. Manifold price will be included shortly.

The carbon intensity of oxygen production has been taken to be 400g CO2 per litre of oxygen.

The cost of oxygen is so small as to make no appreciable difference to the overall cost (£5.00 per 100 m3). The carbon intensity of compressed air production has been ignored.

Using the calculator

  • Choose the tab according to the nature of the carrier gas:
  • a. nitrous oxide/oxygen,
  • b. oxygen air with rotameters or
  • c. set FiO2 and FGF as one might find on an anaesthesia work station
  • Enter the unit cost of your institution's inhalational agent in cells D7 E7 and F7
  • Enter the carrier gas flow rate and the vapouriser setting (%)
  • The graphs adjust automatically
  • The cost graph is labelled £ sterling per hour at that particular FGF and vapou setting
  • The CO2e in kg CO2 per hour at that particular FGF and vapour setting

What the calculator is not

This calculator takes no account of the additional drugs and disposables required to deliver safe anaesthesia. Nor is it a substitute for carefully delivered safe and effective anaesthesia.

Modern anaesthetic gases are expelled into the atmosphere and contribute to anthropogenic climate change. They also represent 5% of the carbon footprint for all acute NHS organisations' (The Lancet Planetary Health - Anaesthetic gases, climate changes, and sustainable practice, 2017)

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