Blog Layout

Occupational exposure of midwives to nitrous oxide on delivery suites.

K.A. Henderson, I.P. Matthews, A. Adisesh, A.D. Hutchings.

Occup Environ Med 20023; 60; 958-961


Study conducted prior to December 2002 using 40 midwives within 2 hospitals covering a total of 46 midwife shifts. 


Passive diffusion tubes were used to determine workplace exposure to nitrous oxide during the first 4hrs of their shift. In addition, pre and post shift urine samples were collected to ascertain biological update.


During 35 out of the 46 midwife shifts exposure levels were greater than the 100ppm TWA occupational exposure limit.  The measurement range was 2.4~1300ppm, mean 313ppm, s.d. 358ppm.


In 43 of the 46 instances nitrous oxide was detected in the midwife urine post shift.  The measurement range was 0~1102µg/l, mean 114 µg/l, s.d. 191µg/l.


Adjusting for baseline urine levels, there was a statistically significant correlation between urinary concentration and environmental concentration of nitrous oxide (p<0.001).


It was noted that 14 of the 20 delivery rooms where the study was conducted had less than the recommended 5~6 air changes per hour.



Approximately half of the midwives had baseline nitrous oxide present in their pre-shift urine sample, which was viewed as a surprising finding.  The authors went on to postulate that the clearance time for nitrous oxide may be longer that currently thought.


by David Mclaughlin 11 November 2024
Greener NHS Provides a road map for a future Net Zero.
9 November 2024
The first production unit was introduced into a delivery suite at UHW, Cardiff mid-August and has been in regular use thereafter. Feedback from midwives was collected both informally and via questionnaire. Key takeaways:  Very positive and supportive of the project in terms of environmental benefit. Staff understand that Entonox is a greenhouse gas and that this machine reduces emissions. Many staff feel it will improve their health and wellbeing by reducing their own exposure to nitrous oxide. The machine was simple and easy to use It was quiet Although large, it was able to fit into the room ok It could be used with a mouthpiece or face mask depending on patient choice It did emit some heat, which although noticeable, didn't make the room uncomfortably hot
9 November 2024
The ability of the N2O Clear product to eliminate nitrous oxide from an inlet stream was evaluated over 2 days at Wrexham Maelor Hospital, north Wales. Using cylinder gas, test flows simulating 1~5 LPM of nitrous oxide and Entonox were introduced into the N2O Clear unit and the exhaust concentration of nitrous oxide was measured using a G200 N2O analyser from QED Environmental Systems. % reduction in nitrous oxide between inlet and exhaust air was then calculated and determined to exceed the target 99% on all occasions.
8 November 2024
Implementing nitrous oxide cracking technology in the labour ward to reduce occupational exposure and environmental emissions: a quality improvement study.
Share by: