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Inhalational Anaesthetic Agents

How do inhalational agents affect the environment? In this article, we discuss their role in global warming.

Inhalational Anaesthetic Agents and Carrier Gases

  • Gases used in everyday clinical anaesthetic practice can negatively impact the environment by increasing the concentration of greenhouse gases (GHGs) +/- depleting the ozone layer
  • Ozone stops the majority of the sun’s harmful UV radiation from reaching the earth’s surface
  • GHGs are transparent to visible light but opaque to infrared radiation
  • GHGs can absorb the earth’s emitted longwave infrared radiation, thus heating the lower atmosphere by slowing the rate at which it can escape into space
  • GHGs differ in their ability to absorb energy (radiative efficiency) and their duration (atmospheric lifetimes)

Radiative Efficiency

  • Measure of ‘greenhouse strength’ for different GHG, defined as the change in radiative forcing per change in atmospheric concentration of a gas
  • Radiative efficiency (watts per metre squared per part per billion)
    • Sevoflurane 0.351
    • Isoflurane 0.453
    • Desflurane 0.469
    • Nitrous Oxide 0.003

Atmospheric Lifetimes

  • Atmospheric lifetime refers to the duration of time a greenhouse gas remains in the atmosphere before being decomposed by chemical processes
    • Sevoflurane 1.1
    • Isoflurane 3.2
    • Desflurane 14
    • Nitrous Oxide 110
  • Does a gas with a long atmospheric lifetime but a low radiative efficiency have a larger or smaller effect on climate than a gas with a short atmospheric lifetime and a high radiative efficiency?

Global Warming Potential (GWP)

  • GWP allows us to compare the impact of various GHGs over a specific period of time with respect to CO2
  • The most commonly employed measure is GWP over 100 years GWP100
  • ​Inhalational anaesthetic GWP variability is predominantly caused by differences in atmospheric lifetime rather than radiative efficiency
  • GWP100
    • Sevoflurane 130
    • Isoflurane 510
    • Desflurane 2540
    • Nitrous Oxide 310

Ozone Depleting Substances (ODS)

  • These are chemicals that destroy the earth’s protective ozone layer. They are also very potent GHGs
  • Ozone- depletion potential (ODP) is a measure of their destructiveness
    • global loss of ozone due to the given substance: global loss of ozone due to CFC-11 of the same mass
  • Nitrous Oxide is currently the dominant anthropogenic ODS
    • ODP of 0.017
    • Anaesthetic nitrous oxide contributes to 1-3% of all global nitrous emissions
  • Atmospheric bromine (Halothane) and chlorine atoms (Isoflurane and Enflurane) form ozone-depleting radicals
  • ODP
    • Halothane 0.36 (obsolete in most countries now)
    • Isoflurane 0.01
    • Enflurane 0.02

Desflurane and Sevoflurane have no ODP as fluorine does not destroy the ozone layer. They do, however, have significant global warming potential.

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Introduction to Using Total Intravenous Anaesthesia (TIVA)

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