Nitrous Oxide

Nitrous oxide is a chlorofluorocarbon (CFC) and an anesthetic agent that is used today in a variety of medical settings, including labour anesthesia, paediatric general anesthesia, and as a carrier gas for other volatile anesthetic agents to speed up induction and recovery. From an environmental perspective, nitrous oxide is unique because it is both a greenhouse gas and the main anthropogenic ozone-depleting substance of the 21^st century.³

The ozone layer is located in the stratosphere 15–35 km above the Earth’s surface. It plays a major role in absorbing UV-B radiation from the sun, preventing high levels from reaching earth’s surface. In doing so, the ozone layer protects humans against risks such as skin cancer and cataracts, as well as guards the health of plants, animals, and microbes. The ozone layer thus is crucial for the maintenance of terrestrial and aquatic ecosystems as well as the global food supply.⁴

Nitrous oxide has a GWP₁₀₀ of 298,⁵ an atmospheric lifespan of 114 years,⁵ and an ozone-depleting potential (ODP) of 0.017.³ Theoretically, to be used on its own in GA, nitrous oxide would require administration at 105% to achieve 1 MAC.¹ Consequently, when mixed with air or oxygen at a 60/40% ratio to act as an adjuvant anesthetic, nitrous oxide decreases the MAC required from other anesthetic gases by its equivalent percentage (i.e. 60%) to approximately preserve a MAC of 1.² Use of nitrous oxide as a carrier gas increases the carbon dioxide equivalent emissions of sevoflurane 30-fold while having a negligible effect on desflurane emissions.²