Please stop using nitrous oxide in routine clinical practice (comment on: Use of nitrous oxide in contemporary anesthesia—an ongoing tug of war)

We would like to comment on the recent editorial by Chan et al.¹ and their remarks on the study by Obeidat et al.,² stressing the role of nitrous oxide (N₂O) in general anesthesia.

In our opinion, it behooves anesthesiologists to weigh the advantages and disadvantages of the anesthetics used—both for the individual patient and for the environment. In this regard, careful consideration of the entire life cycle of drugs and the resultant environmental impact is an important aspect of selecting anesthetics in clinical decisions making. All anesthetics, regardless of whether they are inhaled or intravenously administered, have an impact on climate change.

All inhalational anesthetics are greenhouse gases.³ Their life cycle greenhouse gas emissions include waste gases released into the atmosphere and emissions (mainly CO₂) from other life cycle stages. As we know, desflurane has the greatest impact among anesthetics on life cycle greenhouse gas emissions: 15 times as much as isoflurane and 20 times as much as sevoflurane per minimum alveolar concentration hour when administered in an O₂/air mixture.

Greenhouse gas emissions increase significantly with all drugs when they are administered in an N₂O/O₂ additive. With all inhalational anesthetics, the effects of greenhouse gases are dominated by uncontrolled emissions because of unnecessarily high fresh gas flows. According to the United States Environmental Protection Agency, N₂O accounts for approximately 7% of all greenhouse gas emissions from human activities in the USA, including agriculture, wastewater management, and industrial processes. Nitrous oxide molecules have an atmospheric lifetime of 114 years and a global warming potential of 298; 1 kg of N₂O has almost 300 times the warming impact of 1 kg CO₂.⁴ Furthermore, N₂O contributes to the depletion of the ozone layer. Based on United Nations Framework Convention on Climate Change data, N₂O alone adds an additional 0.7% to the carbon footprint of the healthcare sector for North America. Hence, every effort should be made to reduce the use of N₂O in healthcare. Anesthesia providers can have a huge impact in their daily practice by choosing anesthesia agents with a lower impact on climate change.

As one of the strategies, the use of N₂O should be avoided—this discussion is not new but started as far back as 1989.

Recently, pediatricians and obstetricians have been promoting the use of N₂O for analgesia. This is particularly common in children during painful procedures and during labour and large quantities of N₂O are required for analgesia. Given the increasingly palpable and disastrous effects of global warming and climate change, we believe that one should reject the use of N₂O in pediatrics and obstetrics if there are adequate alternatives available, such as topical local anesthesia for children and epidural analgesia or remifentanil infusions for parturients during labour.

Physicians should avoid unnecessarily high fresh gas flow rates for any inhaled medication. The logical consequence is anesthesia without using a N₂O/O₂ mixture and metabolic flow or at least minimal flow anesthesia.⁵ There is no need for denitrogenation by means of high fresh gas flows, which are necessary to wash in N₂O. Thus, the advantages of rebreathing systems can be used right from the start, with no requirement for initially high fresh gas flows. For more detailed information or references please contact us at c.honemann@icloud.com.

We believe that N₂O should no longer be used in clinical routine today. We stopped using N₂O at the Marienhospital Vechta in 2003. With the introduction of remifentanil, the use of N₂O was abandoned at Bonn University Hospital. After a short period of time, nobody complained about missing N₂O in clinical routine.