Specifications

screaming causing the nurse to be exposed to high levels of nitrous oxide. In other cases nitrous

oxide was used for a short period of time and then Demerol/Gravol or an epidural were given.

Labour and delivery using nitrous oxide present a different situation than the gas is use in the

operating room or the dental office. In this situation the mother controls the nitrous oxide

administration. Hospital protocol states that the gas should only be used during contractions and

not between them. In most cases the mothers removed the mask from their faces between

contractions. This allowed them to talk or scream or just breathe the room air. It would be

challenging to decrease nurses exposure to nitrous oxide in this situation using local exhaust

ventilation. Bernow et al. conducted a study in 1984 using a plastic hood enclosing the mother’s

head. This was a very barbaric suggestion and even though they were successful in reducing the

midwives exposure to less than 25 ppm it is not a solution that would be widely accepted.

Nitrous oxide is known to be off gassed for a period of up to 37 minutes after use. It is not

realistic to force the mother to wear the mask at all times so that the scavenging system picks up

all the nitrous oxide. This would cause the nitrous oxide to be delivered every time the mother

took a breath and could result in an overdose and unconsciousness. A mask that provided nitrous

oxide when the mother presses a button and stops when the button is not depressed could be

worn all the time and oxygen alone would be delivered when the button was not depressed. The

main problem is that it is next to impossible to talk and be understood while wearing the mask.

Control measures to decrease the nurse’s exposure to nitrous oxide would be to increase the

general exhaust ventilation from 9.9 air changes per hour (ACH) to 15 ACH or to increase the

percentage of fresh air going into the room. Substitution or enclosure are not currently viable

options for this situation.

The WCB OF BC 8 hour exposure limit has been set at 25 ppm which gives a calculated 5X

excursion limit of 125 ppm. Previous studies and this study have shown that exposures occur up

to 4X this level (500 ppm). Based on the data presented in this report, the 25 ppm 8-hour

exposure limit can be met in the labour and delivery situation, however, a 125 ppm excursion

limit is not consistently achievable based on the conditions present at the time of this study.