Measurement of scavenged nitrous oxide in the dental operatory.

Recent epidemiological studies suggest that chronic exposure to nitrous oxide may be a health hazard to the dental staff and the ADA has recommended that atmospheric nitrous oxide be controlled by use of a scavenging system. These concerns are of special interest to pediatric dentists because studies have shown that the effectiveness of the scavenging system may be influenced by patients" behavior and talking. This study was undertaken to examine the effectiveness of two ADAapproved scavenging systems. The effects of talking and the use of the rubber dam also were examined. Nitrous oxide levels in the dentist’s breathing zone were measured during 80 standardized dental appointments using nitrous oxide-oxygen inhalation sedation. Air samples were collected continuously and analyzed by infrared spectrophotometry. Results showed a significant difference in the effectiveness of the 2 scavenging systems. Neither the rubber dam nor the patient’s talking significantly affected levels of scavenged nitrous oxide. The use of nitrous oxide-oxygen inhalation sedation in dentistry has increased dramatically the past 25 years.1 Pediatric dentists have found nitrous oxide to be a safe and effective agent in the management of the anxious child patient. Wright and McAuley reported that 44% of pediatric dentists in the American Academy of Pediatric Dentistry used nitrous oxide-oxygen inhalat:ion sedation. 2 In 1980, a similar survey revealed the number of pediatric dentists using nitrous oxide-oxygen inhalation sedation for behavior management situations had increased to 73%. 3 Nitrous oxide was assumed to be safe for both the patient and the dental staff until the late 1960s when epidemiological studies implicated chronic exposure to trace levels of waste nitrous oxide and other anesthetic gases as a possible health hazard to the dentist and staff. The first report suggesting that chronic exposure to waste anesthetic gases may be a potential health hazard was published in 1967 by Vaisman. 4 This study encouraged other investigators to examine the relationship between chronic exposure to nitrous oxide and health problems. Human epidemiologic studies consistently have reported increased rates of spontaneous abortion in exposed females and unexposed spouses of exposed males. 5-1° These studies also have documented significantly increased rates of renal, hepatic, and neurologic disease in exposed individuals as well as congenital abnormalities in their offspring. 8-~° The ADA has recognized the possibility that exposure to trace amounts of nitrous oxide may present a health hazard to dental personnel 1~ and has recommended that such trace levels be maintained at the lowest achievable levels by scavenging systems and other reasonable control measures. After reviewing the available literature, the National Institute of Occupational Safety and Health (NIOSH) established a concentration of 50 parts per million (ppm) as reasonably achievable level of waste nitrous oxide in the dental operatory. 12 The scavenging system has been examined as a simple and inexpensive means of reducing atmospheric concentrations of nitrous oxide. The literature confirms that scavenging reduces pollutant levels; however, the literature is unclear relative to reductions achievable with scavenging measures. Investigations by 2 independent researchers have found significant differences between commercially available scavenging units. 13,14 It also has been suggested that such variables as rubber dam use, ~* patient talk192 NITROUS OXIDE IN THE DENTAL OPERATORY: Christensen et al. ing,15 and patient cooperation 16 may have an effect on the level of waste gas in the operatory. To date, there is little documentation to support these claims. The purpose of this project was to determine the effectiveness of 2 different scavenging units during nitrous oxide-oxygen inhalation sedation of human volunteer subjects. Two additional variables, rubber dam use and patient talking, also were examined. Methods and Materials After Human Subjects Committee approval, 10 adult volunteers ranging in age from 20 to 30 years were selected to participate in the study. Individuals were considered potential subjects if they were at least 18 years of age and in sound health as ascertained from the patient health questionnaire. Potential patients were eliminated if they disclosed health problems requiring special consideration during dental treatment and/or if they felt they might not be able to fully cooperate for a routine operative dental procedure. Signed consent was obtained to proceed with treatment on each individual. Adult subjects were chosen because the Human Subjects Committee required that the subjects understand and approve all possible risks of such a study. Also, it was important that subjects be totally cooperative in order to control carefully the conditions of the study and manipulate the variables of interest. General Procedures Two investigators completed all treatment during a standardized, 15-min dental appointment using nitrous oxide-oxygen inhalation sedation (Table 1). The 3 variables (scavenging mask, talking, rubber dam) were assigned on a random basis (Table 2). All treatment was performed in a single dental suite T,~ete 1. Standardized Dental Appointment Measurement Dental Time of N~O N20 Levels Treatment (min) Test for leakage Continuous 100% 02 sampling 20% N~O 80% 02 30% N20 70% 02