Evaluation of a modified scavenging system to reduce occupational exposure to nitrous oxide in labor and delivery rooms.

We developed a new scavenging mask for the administration of nitrous oxide to mothers-to-be during labor in order to minimize leakage of the patient's exhaled breath into the room and, therefore, decreasing staff exposure to nitrous oxide. The scavenging system was designed with an inner mask for gas delivery, an outer mask to capture exhaled breath, and a continuous exhaust airflow based on breathing flow rates. In this study we field tested the scavenging system by measuring personal exposures of nurses (N = 30) and room air concentrations (N = 33), while patients self-administered nitrous oxide either through the conventional or modified scavenging system. Personal exposures were measured using passive nitrous oxide monitors, and area measurements were made using a direct-reading infrared analyzer. Information about volumes of nitrous oxide used, nurses' movements, and patients' use of the analgesic was recorded in order to examine factors that influenced exposures and the effectiveness of the scavenging system. The new scavenging system significantly reduced exposures in the room and to nurses (arithmetic mean nitrous oxide concentrations = 39.7 ppm and 40.2 ppm, respectively, compared with 82.2 ppm and 69.3 ppm, respectively, for the conventional system). Other factors associated with lower concentrations included larger distances between the nurse and the patient, and greater times since nitrous oxide was used. Observations during the field trial indicated that subjects did not hold the scavenging mask close enough to the face to capture exhaled breath during much of the time when the breath was highly contaminated. Additional modifications to the scavenging system are required to further reduce nitrous oxide concentrations and to improve comfort and usability.