Inhaled Nitrous Oxide and Labor Analgesia

Inhalational anesthetic agents have been used since the mid 1800s to help alleviate pain
associated with labor. James Simpson and John Snow initially utilized ether and chloroform
respectively in 1847 and 1853. Stanislav Klikovich followed in his predecessors footsteps and
successfully administered nitrous oxide for labor analgesia in 1881. Although many
inhalational agents have been considered for labor analgesia since that time, the
administration of nitrous oxide has been refined over the last century and remains a common
practice for obstetrical anesthesia today. Since that time, nitrous oxide has been found to
be an effective labor analgesia for many women, although providing less pain relief compared
then a labor epidural, it has been found to be safe for the mother, baby, and health care
providers.

Nitrous oxide is currently used by 60% of laboring women in the United Kingdom, 50% of women
who deliver in Australia and nearly 50% of all parturients in Canada and Finland. This
compares to a recent article which reported that only two United States hospitals routinely
offer nitrous oxide for labor analgesia as the majority of laboring women request an
epidural. The epidural rate in the Unites States averages nearly 90% compared to only 14-38%
in other parts of the world.

Nitrous oxide is an easy to administer non-flammable, odorless inhalational agent that
produces both analgesia and anxiolysis. It is believed the mechanism of action of nitrous
oxide is through the release of endogenous opioid peptides into the periaqueductal gray area
of the midbrain which stimulates descending noradrenergic pathways resulting in analgesia.
These pathways modulate pain in the dorsal horn of the spinal cord through alpha-2
adrenoreceptors. Anxiolytic effects are thought to be caused by inhibition of
N-methyl-D-aspartate (NMDA) receptors. In a Swedish study involving 1,997 parturients
utilizing inhaled nitrous oxide as the sole anesthetic for labor analgesia, 37.6% of
participants reported effective pain relief.

Currently, the rate of labor epidural analgesia at Magee Womens Hospital is approximately
90%. There are many advantages to the use of nitrous oxide for labor analgesia compared to an
epidural. Complications associated with labor epidural analgesia can include infection,
bleeding, headache, and wet-tap. These complications can result in a prolonged hospital stay
that is not associated with the use of nitrous oxide for labor analgesia.

One of the biggest advantages of the use of nitrous oxide for labor analgesia is the
significantly lower cost to administer compared to an epidural. In a recent article in the
Birth journal, it was noted that the use of nitrous oxide is far less expensive and much
simpler than epidural analgesia and does not result in complications requiring additional
treatments and prolonged hospital stays. The use of nitrous could have major financial
benefits for both Medicaid and private insurance companies. In 2004, the largest cost for
these insurance entities was the cost to care for pregnant and laboring women which was
reported to cost $41 billion. The most significant cost savings would be the reduction in
anesthesia services. Currently average cost per patient for anesthesia staff coverage is 728
dollars. Average re-imbursement for a labor epidural placement is 385 dollars. Nitrous oxide
does not require anesthesia staff to implement, saving health care dollars. After the initial
investment of the nitrous oxide machine, the only additional cost would be the tubing and
mask for the patient and the nitrous oxide and oxygen E-cylinders for delivery.

With Nitrous oxide having many qualities that make it an attractive choice for labor
analgesia, many anesthesia providers are questioning its limited use in the United States. It
is speculated that it may be cultural issue and that women make decisions regarding labor
analgesia based on learned experiences of family and friends, many of whom have not heard of
or used nitrous oxide to cope with labor pains. Another reason may be that some authors argue
that nitrous oxide is an orphan drug with no pizzazz for professional groups or companies to
profit from its use as it causes environmental and occupational hazards which limit its use.
No definitive opinion exists to answer this question. Finally, some authors suggest its use
is limited due to the disadvantages of nitrous oxide, which include the possibility to cause
mood alterations, euphoria, impaired mentation, dysphoria, inappropriate behaviors and nausea
and vomiting. These side effects are limited through a number of fail-safe mechanisms built
into the nitrous oxide machine which includes the delivery of at least 30% oxygen and 3
liters of fresh gas flow. In addition the proper use includes self administration under
direct supervision of a trained provider while the nitrous oxide is in use.

Inclusion Criteria:

- all women of childbearing age (including children aged 14 years and above)who are
pregnant

- parturients who request labor analgesia of family medicine investigators certified in
the use of nitrous oxide for labor analgesia at Magee-Women's Hospital

- informed verbal and written consent

Exclusion Criteria:

- coexisting medical conditions that are contraindications to the use of nitrous oxide
(i.e. recent eye or ear surgery, history of Meniere's disease, history of vitamin B-12
deficiency)

- history of severe nausea and vomiting

- history of chronic pain

- inability to hold a facemask

- impairment of consciousness or intoxication at time of delivery

- received intravenous opioids within two hours prior to initiation of nitrous oxide

- impaired oxygenation (ex: lung cysts, pneumothorax, pulmonary hypertension, or
pulmonary edema) with a room-air pulse oximetry reading less than 95%

- hemodynamic instability

- non-reassuring fetal heart rate tracing

- inability to read, write and understand the English language enough to complete all
survey questionnaires and pain assessment scales.