Nitrous oxide-not a laughing matter
Myron Yaster MD, Peggy Allen, MD, and Elizabeth E. Hansen, MD, PhD
During the holiday break, I’m reposting the most highly viewed PAADs of 2023. This first appeared on October 31, 2023 and was the most highly viewed PAAD in October.
“If it ain’t broke why fix it”? “I’ve always done it this way!” “The amount of medical nitrous oxide waste is a tiny fraction of nitrous oxide emissions compared to that produced in agriculture.”
At this year’s annual meeting of the Society for Pediatric Anesthesia in San Francisco, Dr. Elizabeth Hansen of Project Spruce1 fame once again presented cogent arguments to eliminate or greatly reduce the use of nitrous oxide we use in our pediatric anesthesia practices. Her lecture was coincidentally timed with an open access article by Gordon et al. which appeared on line ahead of print in Pediatric Anesthesia.2 I thought it would be a good time to once again review this topic in the PAAD. Myron Yaster MD
Original article
Gordon DW, Chatterjee D, McGain F. It's time to stop using nitrous oxide for pediatric mask induction. Paediatr Anaesth. 2023 Oct 4. doi: 10.1111/pan.14778. Online ahead of print. PMID: 37792609
Society for Pediatric Anesthesia Annual Meeting (October 2023) Lecture
Elizabeth Hansen: No Laughing Matter: Harm and Waste from Nitrous Oxide
https://www2.pedsanesthesia.org/meetings/2023annual/guide/program/files/2023-CA-1695656298-6720.pdf
Very few drugs have as long a history of safety and efficacy as nitrous oxide. Discovered in 1772 (!!!) by Joseph Priestly (who also discovered oxygen and carbon dioxide) and introduced as “laughing gas” by Humphrey Davy in 1790, nitrous oxide has been safely and extensively used as an anesthetic in surgery and dentistry since 1844, when Horace Wells demonstrated that he could produce anesthesia during 3d molar extractions. Because of its sweet and nonpungent aroma, rapid onset, and ability to speed the mask induction of general anesthesia, with more soluble anesthetic gasses like halothane, it has been a crucial component of pediatric anesthesia for decades. Further, it is used widely outside of the operating rooms in pediatric practice, particularly in emergency medicine and dentistry to facilitate “awake” IV placement and for painful procedures like fracture reductions or 3rd molar extractions.
Obviously, there are some situations when nitrous oxide cannot or should not be used, like when a high FiO2 is needed or when its diffusion into closed air-filled spaces can be harmful. On the whole though, for most pediatric cases it has many effects that practitioners love and many feel “if it ain’t broke why fix it”? In 2021, a SPA poll found that about 80% of respondents use nitrous oxide as part of their inhalation induction for a healthy 4 year old patient.3
So why the push to eliminate it? The continuing use of nitrous oxide has recently been called into question because it is a potent greenhouse gas with a Global Warming Potential (GWP) 265 times that of carbon dioxide.3 Further, nitrous oxide is one of the most potent ozone depleting substances and is “expected to be the most important ozone depleting emission throughout the 21st century.”4
As good citizens, should we eliminate it and is it necessary in our practice? Gordon et al.2 argue that using nitrous oxide is unnecessary and that it should be replaced by other evidence-based techniques to facilitate mask tolerance. Gordon refutes several commonly cited reasons to use nitrous oxide by presenting evidence that use of nitrous oxide does not facilitate tranquil mask placement, does not meaningfully speed inhalation induction, and decreases safety. The risks of occupational exposure present another argument against its use, especially regarding reproductive risks (reduced fertility, pregnancy loss, and risk to fetal development have all been described).
Additionally, nitrous oxide irreversibly inactivates B12, which can result in increased homocysteine levels and decreased DNA synthesis. Studies and case reports of neurological complications from central and peripheral demyelination due to altered myelin formation, as well as bone marrow abnormalities, have been demonstrated for decades. Many of these results do not appear for days to weeks following anesthesia and are thus not often noted.5,6
Fascinatingly, almost all (75-95%) of nitrous oxide waste is caused by system leaks of centrally piped systems rather than its use during an anesthetic.7 Abandoning centrally piped systems, switching back to E cylinders on the anesthesia machine and turning the cylinders off between uses, would thereby dramatically reduce nitrous oxide waste. These interventions are easier to implement when the clinical use of nitrous oxide is low (for example, lower frequency of E cylinder replacements). Thus, the reduction in clinical use helps to drive the larger-impact intervention of abandoning central nitrous oxide delivery systems.
What are you doing in your practice? At the SPA meeting in San Francisco, lecture attendees answered the same poll question as the one in 2021: “During inhalation induction in a 4 y/o 18 kg healthy child (ASA-PS 1), what fresh gas flow combinations will you use?” Out of 109 responses, a majority chose an option without nitrous oxide (50 chose <4LPM, 16 >4LPM 100% O2), and 80% chose an option with <4LPM flow, regardless of if they would use nitrous oxide or not. I (MY) believe that most pediatric anesthesiologists still use nitrous oxide on induction and do not believe Dr. Gordon’s statement that it is unnecessary. What do you think?
For those of you who have joined Project SPRUCE, tell us about your experience and how your staff is dealing with this change. Send your responses to Myron who will post in a Friday Reader Response.
References
1. Hansen EE, Chiem JL, Righter-Foss K, et al. Project SPRUCE: Saving Our Planet by Reducing Carbon Emissions, a Pediatric Anesthesia Sustainability Quality Improvement Initiative. Anesth Analg. Published online May 5, 2023. doi:10.1213/ANE.0000000000006421
2. Gordon DW, Chatterjee D, McGain F. It’s time to stop using nitrous oxide for pediatric mask induction. Paediatr Anaesth. Published online October 4, 2023. doi:10.1111/pan.14778
3. Surya Narayanasamy, Diane Gordon, Elizabeth Hansen, Tracy Wester, Audra Webber, RJ Ramamurthi, Christopher Edwards, James Bradley, Lauren Lobaugh, Katherine Keech, Sheri Jones Oguh, Rajeev Subramanyam, Shivani Patel, Vikram Patel, Neha Patel, Priti Dalal, Brad Taicher. Society for Pediatric Anesthesia Quality and Safety Poll Question; February 2022. SPA. Published March 29, 2021. Accessed September 11, 2023. https://pedsanesthesia.org/poll-of-the-month-archives/
4. Ravishankara AR, Daniel JS, Portmann RW. Nitrous oxide (N2O): the dominant ozone-depleting substance emitted in the 21st century. Science. 2009;326(5949):123-125.
5. Hadzic A, Glab K, Sanborn KV, Thys DM. Severe neurologic deficit after nitrous oxide anesthesia. Anesthesiology. 1995;83(4):863-866.
6. Campdesuner V, Teklie Y, Alkayali T, Pierce D, George J. Nitrous Oxide-Induced Vitamin B12 Deficiency Resulting in Myelopathy. Cureus. 2020;12(7):e9088.
7. Seglenieks R, Wong A, Pearson F, McGain F. Discrepancy between procurement and clinical use of nitrous oxide: waste not, want not. Br J Anaesth. 2022;128(1):e32-e34.