Specifications

13
The sampling procedure for this study consisted of using passive dosimeters, a Miran infra-red
spectrophotometer and the Medigas 3010, personal infra-red active sampler. The nurse wearing
the Medigas 3010 was followed for the duration of the nitrous oxide use and her activities were
noted in an activity log.
4.2.3 Miran
The Miran air intake particulate filter was set up on the fetal monitor located approximately 3
feet from the mother’s head and was turned on at the start of the delivery and turned off at the
end of the delivery or after the administration of an epidural. A Telog data logger was attached
to the Miran to allow the data to be logged and later downloaded to a personal computer. The
telog records results in volts and a nitrous oxide response curve obtained from the WCB of BC
lab was used to convert the values from volts to ppm.
The Miran was calibrated by injecting a 1 mL sample, from a sample bag containing 10,000 ppm
N
2
O, into the Miran when it was set up in a closed loop. The unit was considered stable when it
was injected three times and the same concentration was indicated on the display. The unit was
calibrated at the beginning and end of each 12 hour period and was kept on ‘stand by’ setting
until it was needed.
4.2.4 Medigas 3010 personal sampler
The Medigas 3010 was attached to the nurse as soon as the mother indicated that she wanted to
use nitrous oxide. The pump was attached to her waistband and rubber tubing secured to her
back and over her shoulder and the end of the tube was located in the nurse’s breathing zone
(approximately six inches from her mouth). The tubing was taped to ensure that it did not
interfere with the nurse’s duties and so that it did not form a loop or kink. The unit was switched
off at the end of the delivery or after Demerol or an epidural was administered and therefore
nitrous oxide use ceased.
The nurse was followed the entire time she was wearing this device and her activities were noted
in an activity log.