Annual Anaesthetic Departmental Calculator

Annual Impact Calculator

Striving to reduce the carbon dioxide equivalence (CO2e) of anaesthesia requires calculation of the annual departmental use of anaesthetic vapours and comparing year-on-year the trends. This Excel tool uses the currently accepted values for the global warming potential of the volatile agents and nitrous oxide and calculates the total CO2e attributable to this aspect of anaesthetic and analgesic practice.

  • As cylinder sizes vary between medical gas suppliers choose the BOC-Linde or Air Liquide tab as appropriate. 
  • Obtain the annual pharmacy issue of bottles of the volatile anaesthetic agents issued (and assumed to be used) and the annual cylinder return data for nitrous oxide and Entonox® or Equanox® as appropriate. 
  • Part filled returned cylinders are vented to the atmosphere by the medical gas supplier so the return data will allow calculation of the mass of nitrous oxide released.
  • Enter the values in the cells and the tool calculates the annual figure in tonnes CO2e.

For the record, this version uses 265, 205, 565, and 2720 for nitrous oxide, sevoflurane, isoflurane and desflurane respectively*. If the accepted value for the GWP of any of the agents change, by changing the values in the ‘Settings’ tab, will alter the calculations.

*AR5, the Assessment Report from the IPCC reduced the GWP for nitrous oxide from 295 to 265, though many authors still use the former. The revised figures for the volatile agents are based on the Hodnebrog et al Reviews of Geophysics 2020.

The calculator is badged with the Association of Anaesthetists.