Potential Hazards and Best Practices Associate With Nitrous Oxide in Dental Settings

Explore the research and potential hazards of using N2O, also known as laughing gas, in dental settings.

By Genni Burkhart, DOCS Incisor Editor

This topic is included in DOCS Education's top 25 Safety Statements, compiled by our esteemed faculty. The first ten, by Dr. Leslie Fang, can be found here

 

Nitrous oxide, also known as N2O, is a highly dependable inhalation anesthetic that offers effective sedation and analgesia. When administered correctly, it's considered a safe anesthetic option. Yet, medical professionals who frequently administer it should be aware of potential hazards associated with long-term exposure.

This article will examine the research and possible side effects of N2O exposure in dental settings, commonly known as laughing gas.

Retrospective Studies

In 1967, Vaisman(1), a Russian scientist, reported that female and male anesthesiologists experienced reproductive issues at a much higher rate than the general population. Given that N2O was a common denominator in the anesthetic applications studied, it was implied as the causative agent.

In the 1970s and 80s, Ellis N. Cohen, MD, a Stanford University School of Medicine anesthesiologist whose research revolutionized operating room design, published articles(2) on anesthetic health hazards.

One of Cohen's studies surveyed over 50,000 dentists and dental assistants exposed to trace anesthetics. The results suggested that long-term exposure to anesthetic gases could lead to general health problems and reproductive difficulty for those exposed to trace anesthetics. The results indicated that long-term exposure to anesthetic gases could be associated with an increase in general health problems and reproductive difficulty.

Although research studies have continued to reveal the potentially harmful effects of chronic exposure to N2O, it's important to note that these studies have been retrospective. As a result, there may be biases in the study design that could affect the accuracy of the results. Due to these flaws, whether there's a causal relationship between an individual's exposure to N2O/O2 and reproductive issues cannot be definitively established.

Dental Setting Exposure

In 1977, the National Institute for Occupational Safety and Health (NIOSH) evaluated the scavenging potential of equipment used in operating rooms and outpatient settings. They found that achieving 25 ppm of N2O was possible in the operating room but not in a dental operatory.

As a result, NIOSH established a maximum exposure limit of 50 ppm for personnel in a dental setting. Although the Occupational Safety and Health Administration (OSHA) has not strictly enforced this limit, it's still the recommended standard.

Despite the negative publicity N2O has received, other studies have claimed that no harmful health effects are associated with chronic exposure to N2O, especially in low concentrations.

Further Evaluation Indicates Exposure Duration Factor

In 1995, the University of Colorado conducted a worldwide literature search on biohazards associated with N2O use. Their literature review indicated no scientific basis for the previously established threshold levels for the hospital operating room or the dental setting. This result led to a meeting of interested parties representing dentistry, government, and manufacturing. A formal position statement stating that a maximum N2O exposure limit in parts per million has not (yet) been determined.

There is some evidence that chronic exposure to high levels of N2O affects reproduction. Still, no evidence has been found to date that a direct causal relationship exists between reproductive health and scavenged low levels of N2O.

Sweeney et al.(3) conducted a study that showed the first indication of any biological effect from N2O was observed at a chronic exposure level of 1800 ppm. Experts agree that 400 ppm is a reasonable exposure level significantly below the established biological threshold. (Sweeney et al.)

N2O does interfere with the enzyme methionine synthase, which recycles homocysteine back to methionine. Methionine synthase is crucial in the metabolic pathways of vitamin B12 and folic acid and the production of DNA. Therefore, prolonged exposure to N2O can lead to megaloblastic hematopoiesis and leucopenia.

It's also hypothesized that this interference might impair fetal development. In animal studies, pregnant rats exposed to approximately 60% N2O for 24 hours experienced miscarriage and other fetal abnormalities. This research suggests that chronic exposure to N2O can result in neurologic disorders such as myeloneuropathy.

While symptoms such as sensory and proprioception impairment may be permanent, they are usually temporary with slow recovery.

Recommendations

It’s recommended to postpone the use of N2O sedation during pregnancy due to the high demands for folic acid during organogenesis (first trimester) and the link between high levels of homocysteine and congenital disabilities. For pregnant women working in environments where N2O is used, it's crucial to know the levels of N2O exposure and to use all recommended trace gas scavenging methods.

Dental professionals should decide, depending on the individual and the situation, whether to avoid the office setting and any N2O exposure during the first trimester.

Discussions are ongoing regarding the safety of N2O. However, the gas appears safe when administered in low therapeutic doses for short periods. The dental team must take several measures to maintain safe levels of N2O in the operatory. This includes:

  • A scavenging system can redirect N2O outside the office, which is the most effective method. A scavenging mask system has become standard on all product lines in the US and Canada. When expired, N2O is exhaled through the nose. Vacuum suction ports transport the gas through the central suction to the outside atmosphere. NIOSH has established that an evacuation flow rate of 45 L/min is optimal.
  • Good ventilation in the operatory can dilute the concentration of the gas.
  • Well-fitting masks can reduce leakage. One of the newest advances in nitrous oxide administration is the Safe Sedate Nasal Hood. This apparatus provides more efficient delivery of gases into the nasal nares while reducing extraneous nitrous oxide into the operatory. It is also latex-free and disposable, preventing cross-contamination.
  • Reducing talking by the patient decreases the exhalation of nitrous oxide into the operatory environment.
  • Gas can leak at any connection on the equipment, including the manifold, wall-mounted connections, and associated hoses. Conducting tubing and the reservoir bag are also areas of concern. Because these materials break down over time, they can crack and leak around pleats and seams.
  • The soap and water method for determining leaks is recommended for inspecting these areas. Bubbles after applying soapy water indicate a gas leak.
  • Various commercially available monitoring systems can alert dental staff to potentially unsafe N2O exposure levels. These systems include infrared (IR) spectrophotometry, time-weighted average (TWA) dosimetry, and hand-held monitoring devices.

In Conclusion

No direct evidence shows chronic low-level exposure to N2O causes prolonged and permanent biological effects. Yet, the maximum safe concentration of N2O isn’t fully understood. That's why all dental team members should take safety measures to reduce the level of trace N2O they're exposed to. Furthermore, dental practitioners must be cautious when their health and coworkers' well-being are at stake.

All dental professionals who use N2O/O2 sedation should continue their education and have evidence of proper training with state-of-the-art equipment and N2O administration techniques.

References:

  1. Vaisman A: Working conditions in surgery and their effect on the health of anesthesiologists, Eksp Khir Anesterziol 3:44, 1967.
  2. Cohen, E.N., Bellville, J.W. and Brown Jr., B. (1971) Anesthesia, Pregnancy, and Miscarriage: A Study of Operating Room Nurses and Anesthetists. Anesthesiology, 35, 343-347.
  3. Vallejo MC, Zakowski MI. Pro-Con Debate: Nitrous Oxide for Labor Analgesia. Biomed Res Int. 2019 Aug 20;2019:4618798. Doi: 10.1155/2019/4618798. PMID: 31531352; PMCID: PMC6720045.

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Author: With over 14 years as a published journalist, editor, and writer, Genni Burkhart's career has spanned politics, healthcare, law, business finance, technology, and news. She resides in Northern Colorado, where she works as the editor-in-chief of the Incisor at DOCS Education.

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