Exposure to nitrous oxide in delivery suites at six Swedish hospitals.

ABSTRACT

OBJECTIVE: This study presents occupational peak and average exposures to nitrous oxide in delivery suites in six Swedish hospitals and evaluates different scavenging techniques. METHODS: Exposure measurements based on four consecutive 2-h samples (n = 111) were used to calculate 8-h time-weighted averages (8-h TWAs) for 36 midwives and assistant midwives. Short-term (15 min) samples to study peak exposure were also included in the monitoring program. Diffusive samplers were used for monitoring, and analyzed by thermal desorption and gas chromatography-mass spectrometry (GC-MS). The effect on exposure of different types of scavenging systems was studied by mixed model analysis. RESULTS: The 8-h TWA (n = 36) nitrous oxide concentrations varied between 2.5 and 260 mg/m3, and the geometric means for all the 8-h TWAs was 17 mg/m3 for the midwives and 42 mg/m3 for the assistant midwives. Around 25% of all the 8-h TWAs exceeded the American Conference of Industrial Hygienists' (ACGIH) threshold limit value (TLV-TWA) of 90 mg/m3 (50 ppm). For the short-term samples (n = 29) the nitrous oxide levels varied between 19 and 4,200 mg/m3, and 14% exceeded the Swedish occupational exposure ceiling limit value of 900 mg/m3. The 8-h TWAs were four times higher when the non-ventilated and ventilated simple masks were compared to the double mask (P = 0.02). This trend, although not statistically significant, was also seen for the short-term samples. CONCLUSION: A diffusive sampling method and a GC-MS analytical technique was used for long- and short-term sampling of nitrous oxide. A large number of TWAs exceeded the ACGIH-TLV. Mask connected to scavenging systems significantly reduced the exposures. Furthermore, using a forced general air ventilation system in addition to improved work and delivery routines for the staff and the mother-to-be substantially improved the air quality in the delivery suites.