Policy on Minimizing Occupational Health Hazards Associated with Nitrous Oxide

Purpose

The American Academy of Pediatric Dentistry (AAPD) recognizes that exposure to ambient nitrous oxide (N₂O) may be an occupational health hazard for dental personnel and encourages practitioners to take all precautions to minimize associated risks.

Methods

This policy was developed by the Clinical Affairs Committee, adopted in 1987¹ , and last revised by the Council on Clinical Affairs in 2018² . This update used electronic database and hand searches of articles in the medical and dental literature using the following parameters: terms: nitrous oxide, occupational exposure, AND dentistry; fields: all; limits: within the last 10 years, English. Additionally, recommendations from the National Institute for Occupational Safety and Health (NIOSH) were reviewed.^3,4 Expert opinions and best current practices were relied upon when sufficient scientific data were not available.

Background

Nitrous oxide is an inhalation agent commonly used in dentistry for analgesia/anxiolysis. When used in accordance with recommended techniques and patient selection criteria, N2 O/oxygen inhalation exhibits a high degree of efficacy and patient safety in the clinical setting.^5-9 Occupational exposure to ambient N2 O has been studied for decades, yet the effects of ambient N2 O exposure on dental personnel remain uncertain. Early reports, many of which came from animal studies¹⁰ and/or preceded scavenging devices¹¹ and ventilation systems, implicated chronic occupational exposure of unscavenged N2 O in reproductive effects^10,12,13 (e.g., decreased sperm count, spontaneous abortions¹⁴, birth defects^10,15), liver¹⁴ and kidney damage^10,12,15, and neurologic considerations^10,15 (e.g., memory, hearing). In offices using scavenging systems, female dental staff frequently (i.e., three or more days a week) exposed to N2 O were found to have no elevated risk of spontaneous abortion.^16,17 A paucity of clinical research establishing a causal relationship between chronic exposure of dental personnel to N2 O and health problems continues. A recent systematic review on workplace exposure to volatile anesthetics including N2 O reported evidence is both scarce and inconsistent regarding adverse effects.¹⁸ The dentist’s exposure often is noted to be greater than that of the dental assistant.^19-21 Exposure may increase due to patient factors, with a three-fold increase in ambient N2 O levels noted when patients talked, cried, or held their breath during administration of local anesthesia.²² Furthermore, as the concentration of administered N2 O increases, so does the ambient N2 O level in the operator’s breathing zone.²²

NIOSH reported in 1977 that primary concerns of chronic N2 O exposure were diminished cognition, performance, audiovisual ability, and dexterity; conclusions on reproductive health were not definitive. ¹⁰ That report included a recommended exposure limit (REL) to a time-weighted average (TWA) of 25 parts per million (ppm) yet noted 25 ppm might not be achievable and was subject to review and revision.²³ Shortly thereafter, NIOSH published a technical report intended to help limit occupational exposure in the dental setting to 50 ppm²⁴ although the REL remained unchanged25. In 1986, the American Conference of Governmental Industrial Hygienists established the threshold limit value (TLV) for N2 O exposure at 50 ppm.²⁵ Unless a state or the federal government adopts a TLV, this level is merely a recommendation.²⁶ Only the Occupational Health and Safety Administration (OSHA) can establish a legal limit for exposure (permissible exposure limit [PEL]).²⁶ Notably, OSHA has not established a PEL for N2 O exposure in the healthcare setting.²⁵ The International Labor Organization and World Health Organization also have established a TLV of 50 ppm as TWA and noted that N2 O is not carcinogenic.²⁷

The introduction of methods to scavenge N2 O and other control measures has been effective in reducing ambient N2 O in the dental environment.^21,28 System maintenance, scavenging of expired gases, ventilation of the operatory/room air exchange, use of the minimal effective dose, and patient selection⁹ and management are important to maintaining the lowest practical levels in the dental environment.^3,4,29 Leaks at system connectors and degradation, cracks, and tears in system components may allow N2 O to enter room air, increasing  occupational exposure. Frequent and continual inspection will allow timely maintenance and replacement of components thereby minimizing environmental exposure.³⁰ A doublechamber mask delivery system has been shown to be more effective in the removal of waste N2 O than a single-chamber mask with a scavenging cap.^31,32 Use of a well-fitted doublechamber mask with recommended scavenging system flow rate can decrease occupational exposure to N2 O.^31,33 Recently, disposable masks and mask/circuits have been developed and marketed for improved infection control, but studies comparing their efficacy in scavenging waste gases are lacking.

Establishing a balance of gas flows entering and exiting the delivery system is important for effectiveness and decreasing ambient levels. If the flow of inhalation gases overinflates the breathing bag, excessive leakage from the mask can occur.⁴ Allowing the bag to expand and collapse with each breath ensures proper delivery of gases. Likewise, the rate of suction of the exhaled gases needs to be sufficient to allow removal of gases from the system but maintain the desired clinical effects. NIOSH has recommended that the exhaust ventilation of N2 O from the patient’s mask be maintained at an air flow rate of 45 liters per minute and vented outside the building away from fresh air intakes.⁴ However, scavenging at this rate has been shown to reduce the level of psychosedation achieved with N2 O inhalation.³⁴

Additional steps can be taken to lower the ambient N2 O levels. Ambient concentration will change with increased room air turnover and percentage of fresh air intake. One hundred percent clean outdoor air has been recommended for dental operatory ventilation.³ Well-separated supply and exhaust vents allow good mixing and prevent short-circuiting.³ Use of supplemental measures, such as high-volume dental suction placed in proximity to the mouth^22,35 and administration of 100 percent oxygen following termination of N2 O flow³⁶, has been shown to reduce ambient N2 O levels significantly. Measuring levels of N2 O in the dental operatory can be helpful in determining the type and extent of remediation necessary to decrease occupational exposure.

Patient selection is an important consideration in reducing ambient N2 O levels.^9,29 Patients who are unwilling or unable to tolerate the nasal hood and those with medical conditions (e.g., obstructive respiratory diseases, emotional disturbances, drug dependencies) that contraindicate the use of N2 O are candidates for other behavior guidance techniques.^9,29 In the dental environment, patient behaviors such as talking, crying, and moving have been shown to result in significant increases in baseline ambient N2 O levels despite the use of the masktype scavenging systems.^22,37 Titration of N2 O concentration levels in relation to procedure difficulty can help lower levels of ambient N2 O. N2 O can be discontinued once adequate anesthesia is achieved³⁸, or decreased levels can be maintained during easier procedures and increased for stimulating procedures³⁹.

Policy statement

The AAPD encourages dentists and dental auxiliaries to maintain the lowest practical levels of N2 O in the dental environment. The AAPD also encourages practitioners to weigh the risks and benefits of using N2 O when treating pediatric patients. Adherence to the following safety practices can help minimize occupational exposure to N2 O.

• Educate dental personnel on minimizing occupational exposure to and potential abuse of nitrous oxide.
• Use scavenging systems that remove N2 O during patient’s exhalation.
• Ensure that exhaust systems adequately vent scavenged air and gases to the outside of the building and away from fresh air intake vents.
• Use, where possible, clean outdoor air for dental operatory ventilation.
• Monitor ambient N2 O levels in dental operatories in accordance with local and state regulations.
• Implement a plan for careful, regular inspection and maintenance of the nitrous oxide/oxygen delivery equipment according to manufacturer’s recommendations.
• Carefully consider patient selection criteria (e.g., tolerance of nasal hood, ability to breathe from the nose, cooperative potential, recent illnesses, indications, contraindications) prior to administering N2 O.
• Select a properly-fitted double-chambered mask size for each patient.
• During administration, visually monitor the patient and titrate the flow/percentage to the minimal effective dose of N2 O.
• Encourage patients to minimize talking, moving, and mouth breathing during N2 O administration.
• Use high volume dental suction when possible during N2 O administration.
• Use a rubber dam or isolation devices with suction evacuator when possible during operative treatment.
• Administer 100 percent oxygen to the patient for at least five minutes after terminating N2 O flow to replace the N2 O in the gas delivery system.

The AAPD encourages an interprofessional approach between dental team members who are pregnant or trying to conceive and their physicians regarding the effects of N2 O on reproductive health to assure comfort and safety with the administration of nitrous oxide/oxygen analgesia/anxiolysis.

The AAPD encourages research on the efficacy of newerstyle (e.g., disposable mask, disposable mask/circuit) nasal hoods in scavenging waste gases. Furthermore, because of the paucity of literature on health effects of occupational N2 O exposure in the dental setting with modern delivery, scavenging, ventilation, and monitoring systems, the AAPD encourages additional studies and periodic review of the occupational exposure recommendations by NIOSH.