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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.

This article is from the free online

Introduction to Using Total Intravenous Anaesthesia (TIVA)

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