The Biologic Basis for Administration of Nitrous Oxide/Oxygen Sedation
Nitrous oxide/oxygen (N2O/O2) sedation is a safe and effective means of reducing pain and anxiety for patients around the world, and its safety record spans more than 160 years.
Nitrous oxide/oxygen (N2O/O2) sedation is a safe and effective means of reducing pain and anxiety for patients around the world, and its safety record spans more than 160 years. Nitrous oxide/oxygen sedation has been used in the dental setting since its analgesic properties were discovered in the 1800s. While it continues to be used as an adjuvant anesthetic agent in operating rooms, its routine use now spans several health disciplines in the ambulatory setting within the emergency medical system. Nitrous oxide/oxygen administration is expanding worldwide, which was recently evident by its inclusion into the dental school curricula at Beijing University in China.
Health-care providers should not be this casual about the health of those who are chronically exposed to waste nitrous oxide.
Because of the pharmacokinetic properties of nitrous oxide, it has several advantages over other methods. Nitrous oxide provides both analgesia and anxiolysis, plus has a slight amnestic effect. It provides a rapid onset without the latent period required with oral sedation. Titration is possible with the continuous flow of nitrous oxide and oxygen equipment traditionally used in the dental setting. This delivery method provides the exact amount of drug needed for the desired outcome. Nitrous oxide is delivered as definitive amounts in incremental doses in order to observe patient response and determine appropriate sedation. This delivery is the standard of care for dental professionals because it provides the greatest patient comfort and safety. Recovery from N2O/O2 sedation is quick, as more than 99 percent of all nitrous oxide is expelled from the lungs minutes after the drug is discontinued. When nitrous oxide/oxygen administration concludes, it is standard to provide the patient with 100 percent oxygen until he/she is fully recovered. Also, nitrous oxide/oxygen sedation can be used on most patients with few side effects.
There are very few contraindications to the use of N2O/O2 sedation in an ambulatory setting. In many situations, postponement of this sedation method is recommended until specific conditions are resolved.
Relative contraindications for the administration of nitrous oxide are listed below. Medical consultation is recommended for several of the following conditions.
- The first trimester of pregnancy
- Nasal obstruction associated with upper respiratory tract infections (i.e., sinusitis)
- Altered mental states (i.e., drug and/or alcohol intoxication)
- Recent eye surgery with intraocular gas (i.e., retina and macular hole repair)1
- Patients who take the anti-neoplastic antibiotic, bleomycin2
- Phobic individuals (i.e., dental phobia, claustrophobia)
- Situations in which a patient is unable to understand procedure (i.e., certain mind-altering conditions dependent on the individual, communication barriers)
- Certain chronic obstructive pulmonary diseases
- Some patients with cystic fibrosis
- Recent tympanic membrane graft3
- Persons with certain mental illnesses
There is a lot of concern about nitrous oxide toxicity. This relates primarily to those chronically exposed to nitrous oxide rather than those exposed infrequently during patient treatment. Evidence-based science allows nitrous oxide to be administered without ignorance or prejudice. There has never been any debate about patients having any residual effects from clinically administered nitrous oxide.
The issue of biologic safety of those who are occupationally exposed to nitrous oxide was first raised in literature in the late 1960s. A. Vaisman, a Russian anesthesiologist, claimed in a retrospective study that a high number of reproductive health problems existed in anesthesiologists as opposed to the general population.4 Several subsequent publications claimed greater risk for those chronically exposed to trace waste gas. This led the National Institute of Occupational Safety and Health in 1977 to determine a standard of 50 ppm (parts per million) as the exposure limit for personnel in the dental setting. Although this number was not based on confirmed scientific biologic data, it remains the standard to which dental offices are held. In fact, the first demonstrated biologic change was found to occur at 1,800 ppm nitrous oxide.5
The validity of the literature was investigated under the direction of the author at the University of Colorado in 1995. It was concluded that, despite flawed research designs, there was evidence that reproductive toxicity is associated with high levels of unscavenged waste gas. To date, there is no evidence that a direct causal relationship exists between reproductive health and scavenged low levels of nitrous oxide. The relationship between adverse reproductive outcomes and vitamin B12-deficient individuals is still being investigated.6
Following Clark’s review of the literature, the American Dental Association Council on Scientific Affairs and Council on Dental Practice proposed a position statement that said a maximum nitrous oxide exposure limit had not been scientifically determined. It urged governmental agencies to create new recommendations based on true scientific evidence. Their statement also provided several suggestions regarding best practices for minimizing nitrous oxide trace gas.7 (See sidebar on previous page for current recommendations.)
Product manufacturers and the Occupational Safety and Health Administration (OSHA) are excellent resources for calibration and assessment of trace gas. Additional resources can be found in the Handbook of Nitrous Oxide and Oxygen Sedation by Clark and Brunick. Health care providers cannot be casual about the health of those who are chronically exposed to waste nitrous oxide. Dental practitioners must be diligent and vigilant about the environment in which they practice, and should continuously evaluate the safety of the workplace.
The use of nitrous oxide/oxygen sedation is a safe and effective way to manage patient pain and anxiety in the dental setting. Some state laws governing dental practices now allow dental hygienists and dental assistants to administer nitrous oxide following appropriate training. Currently, 26 states allow dental hygienists to administer nitrous oxide/oxygen sedation, and at least two allow dental assistants to administer this sedation. Each state requires the direct supervision of a dentist. As we assist with access to care issues, it is reassuring to know that the comfort of our patients continues to be a vital part of patient care. OSAP
Morris S. Clark, DDS, FACD, is the Professor, Oral and Maxillofacial Surgery and Director of Anesthesia, School of Dentistry and Professor of Surgery, School of Medicine, University of Colorado Health Sciences Center.
Ann L. Brunick, RDH, MS, is Professor and Chairperson of Department of Dental Hygiene at the University of South Dakota.
1. Hart RH, Vote BJ, McGeorge AJ, et al. Loss of vision caused by expansion of intraocular perfluoropropane (C3F8) gas during nitrous oxide anesthesia. American Journal of Opthalmology 2002; 134 (5), 761-3.
2. Fleming P, Walker P. Bleomycin therapy: a contraindication to the use of nitrous oxide-oxygen psychosedation in the dental office. Pediatric Dentistry 1988; 10(4), 345-6.
3. Munson ES: Complications of nitrous oxide anesthesia for ear surgery. Anesthesiology 1993; 11(3), 559.
4. Vaisman A. Working conditions in surgery and their effect on the health of anesthesiologists. Eksp Khir Anesteziol 1967; 3, 44.
5. Sweeney B, et al. Toxicity of bone marrow in dentists exposed to nitrous oxide. Br Med J 1985; 291, 567.
6. Louis-Ferdinand RT. Myelotoxid, neurotoxic and reproductive adverse effects of nitrous oxide. Adverse Drug React Toxicol Rev 1994; 13(4), 193-206.
7. ADA Council on Scientific Affairs, ADA Council on Dental Practice. Nitrous oxide in the dental office. J Am Dent Assn 1997; 128, 364.
8. Henry RJ, Borganelli GN. High-volume aspiration as a supplemental scavenging method for reducing ambient nitrous oxide levels in the operatory: a laboratory study. Inter J Ped Dent 1995; 5, 157-161.
Current recommendations for best practices for minimizing nitrous oxide trace gas
- The standard of care for N2O/O2 delivery includes the use of scavenging equipment. It is mandatory to use a scavenging nasal hood that allows for exhaled gas to be captured and directed to a vacuum system. Scavenging nasal hoods should fit the patient’s face and be tightened so there is no leakage. Patient talking should be minimal and nose breathing encouraged at all times during sedation.
- The vacuum/suction system should be adequate and vented to the outside away from fresh-air intake vents. High-speed evacuation near the patient’s mouth can provide additional assistance in reducing trace gas.8
- It is important to ensure adequate room ventilation without recirculating room air. Oscillating floor fans can supplement the elimination of trace gas.
- Inspect reservoir bags and conduction tubing for cracks and tears. All connections and fittings should be checked for leaks.
- Flowmeters should be periodically calibrated and evaluated for any needed maintenance.
- All machines must have a fail-safe feature to prevent the inadvertent delivery of 100 percent nitrous oxide.
- Monitor ambient air and breathing zones using infrared spectrophotometry and time-weighted average dosimetry badges.