Monitoring of Nitrous Oxide in Operating Rooms: Identification of Sources and Estimation of Occupational Exposure

: In an academic hospital, nitrous oxide (N2O) levels were measured continuously and detailed workplace observations made in three different operating rooms for 18 days. The study was designed to determine the exposure of different categories of staff to nitrous oxide, to localize and quantify the emissions, and to predict and validate the effect of corrective measures. Nitrous oxide levels appeared to be highly time and place dependent; all staff, except for surgeons, were exposed to N2O levels (8-hour time-weighted average) above 25 parts per million. The most important contributor to total release of N2O was the ventilator (about 70%), especially during artificial respiration of the patient. A simulation model was developed and used to predict the effect of technical improvement of the ventilators and use of scavenging during anesthesia (total 58% reduction of release). The model shows that under these conditions, without altering room ventilation rates, room air circulation can be increased up to 50% without exceeding the proposed threshold limit value (25 parts per million). Measurement of N2O levels after intervention showed a reduction in the area surrounding the ventilator of about 80%, thereby reducing occupational exposure of all staff to below 18 parts per million.