Specifications

3
In 1990 Blair et al., reviewed epidemiological evidence of the relationship between occupational
formaldehyde exposure and cancer. They reviewed 32 epidemiological studies and found an
excess of brain cancer, colon cancer and leukemia among embalmers, anatomist and funeral
directors. They noted that these professions are exposed to a wide variety of chemicals and
therefore there are many potential causes of these excess cancers. The excess colon, brain
cancers and leukemia were not seen in industrial workers exposed to formaldehyde and therefore
it is possible that other chemicals are responsible for the excess (Blair et al, 1990).
2.2 Nitrous Oxide
Nitrous oxide is used in the labour and delivery as a 50% oxygen/50% nitrous oxide mixture
often referred to as Entonox or Nitronox. Nitrous oxide is an odourless, non-combustible gas
that is manufactured by the thermal decomposition of ammonium nitrate and purification of its
byproducts (McGlothlin et al., 1994). The gas has a density of 1.53 which is heavier than air
(1.0) meaning that it will settle towards the ground. For this reason, it is recommended that the
ventilation systems for rooms in which nitrous oxide is used have the fresh air supply located in
the ceiling and the exhausts at floor level (Heath et al., 1994).
The main route of nitrous oxide exposure is inhalation and once it is taken into the body it is
dissolved in blood as a gas and eliminated via exhalation from the lungs in a virtually unchanged
state. A small amount is eliminated through the pores in the skin. After exposure has ceased, the
majority of the nitrous oxide is eliminated from the body in 17 to 35 minutes (McGlothlin et al.,
1994).
2.2.1 Labour and Delivery
The majority of studies examining nitrous oxide exposure have focussed on the operating room
or dental offices. Very few articles have been written about nitrous oxide use in the labour and
delivery room. Labour and delivery represents a unique situation where the nitrous oxide is
administered by the patient.