Specifications

Delivery 4 and Delivery 5 labour and deliveries occurred simultaneously. Delivery 4 was

monitored for the entire labour and delivery and after the baby was delivered at and the Medigas

was moved into the Delivery 5 room.

Delivery 6 used nitrous oxide from just before the Medigas 3010 unit was attached to the

attending nurse and until 9:38 pm when the mother was taken to the high risk room and a

cesarean section was performed under general anesthetic. The nurse who attended to this

delivery had an average exposure of 15.1 ppm for her 12 hour shift. She was exposed to nitrous

oxide during the mothers’ self-administration and during the general anesthetic administration

since it too involves the use of nitrous oxide.

Delivery 7 used nitrous oxide for the entire delivery, however, only the first hour and a half were

captured using the Medigas 3010. Three spikes occurred during the first 30 minutes of the

delivery. The mother used the gas intermittently and exhaled into the mask. Two of the spikes

occurred when the nurse was near the mother’s face between contractions and therefore the

mother was off-gassing into the room.

The passive dosimeter results indicate that one nurse was exposed to an 8 hour TWA of 4.1 ppm

of nitrous oxide during her 8 hour shift when the only delivery she attended did not use nitrous

oxide. Discussions with Chris Thompson indicated that the exhausts from the delivery rooms are

attached to a return system located in the sub-basement of the building and that the air is mixed

with outside air before it is re-distributed throughout the building. This means that a portion of

the air is recirculated, however, the likelihood of a significant concentration of nitrous oxide

returning to the labour and delivery suites is very low under normal operating conditions. The

scavenging system is an exhaust system that is vented directly to the outside via a tunnel that

travels under a road and exits at ground level near a bush covered area. The reason for this

nurses’ level of exposure remains unclear.

The data collected in this study indicate that every delivery represents a unique situation. In

some cases the mothers used the gas and kept the mask on between contractions, in other cases

the mask was removed as soon as the contraction was over and the mother started talking or