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


CONCLUSIONS
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.
Westberg
Håkan
H
Department of Occupational and Environmental Medicine, Orebro University Hospital, 701 85 Orebro, Sweden. hakan.westberg@orebroll.se
Egelrud
Liselott
L
Ohlson
Carl-Göran
CG
Hygerth
Mona
M
Lundholm
Cecilia
C
D000395:Air Pollutants, Occupational / Q000032:analysis*; D000773:Anesthesia, Obstetrical; D003696:Delivery Rooms; D004784:Environmental Monitoring; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D015920:Gas Scavengers; D006801:Humans; D008880:Midwifery; D009609:Nitrous Oxide / Q000032:analysis*; D016273:Occupational Exposure / Q000032:analysis*; D013548:Sweden; D014691:Ventilation / Q000295:instrumentation*
D000395:Air Pollutants, Occupational; D009609:Nitrous Oxide