Anaesthetic Gases

Chlorine and bromine atoms in atmospheric IAAs are cleaved from the parent molecule by ultraviolet radiation, and react with ozone (O3 – which normally absorbs most UVb and UVc, and some UVa, in the stratosphere) to produce oxygen and ‘inert’ chlorine/bromine monoxide, so interrupting the protective oxygen-ozone cycle and depleting the ozone layer, in turn placing living organisms at risk of damage from excess ultraviolet radiation.

By absorbing infrared radiation reflected from the earth’s surface and re-emitting the radiation back towards the surface rather than outward into space, IAAs contribute to ‘radiative forcing’ and the greenhouse effect.

The relative contribution of a greenhouse gas towards global warming may be described by a number of methods. The most frequently reported relating to anaesthesia is the Global Warming Potential, or GWP, which is a measure of  the relative contribution of a mass of IAA to an equivalent mass of CO2  (GWP 1). A number of papers have quoted GWPs based on laboratory measurement of infrared absorption and the spectral location of the absorbing wavelengths. As the global warming effect of IAAs decreases over time due to atmospheric/UV degradation, GWPs are usually appended by a number indicating the GWP over a time period in years.

  Atmospheric lifetime (years) GWP20 GWP100
Sevoflurane 1.8 720 210

Isoflurane

3.2 1800 510
Desflurane 8.9 5090 1620

The global warming potentials of sevoflurane, isoflurane and desflurane.

The global warming effects of IAAs may be ameliorated through use of low-flow anaesthesia, and methods of exhaust gas scavenging and capture.

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Excel ® Version of CO2e and cost calculator of inhalational anaesthesia

Dr Tom Pierce has created an Excel ® Version of CO2e and cost calculator of inhalational anaesthesia. The calculator allows comparison of both financial cost and carbon dioxide equivalence (CO2e) of inhalational anaesthesia. By completing the cells the calculator provides a graphical comparison of cost and CO2e as well as allowing inter-agent comparison. The calculator is a tool that permits financial and environmental comparison between inhalational techniques. The calculator is now available to download on Android by searching 'Anaesthetic Impact Calculator'. The calculator will shortly be available on IoS devices.

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