Nitrous oxide, a colorless, odorless gas, has long been used for labor analgesia in many countries, including the United Kingdom, Canada, throughout Europe, Australia, and New Zealand. Recently, interest in its use in the United States has increased, since the US Food and Drug Administration (FDA) approval in 2012 of simple devices for administration of nitrous oxide in a variety of locations. Being able to offer an alternative technique, other than parenteral opioids, for women who may not wish to or who cannot have regional analgesia, and for women who have delivered and need analgesia for postdelivery repair, conveys significant benefits. Risks to its use are very low, although the quality of pain relief is inferior to that offered by regional analgesic techniques. Our experience with its use since 2014 at Brigham and Women’s Hospital in Boston, Massachusetts, corroborates that reported in the literature and leads us to continue offering inhaled nitrous oxide and advocating that others do as well.1–7 When using nitrous oxide in your labor and delivery unit, or if considering its use, keep the following points in mind.
A successful inhaled nitrous oxide program requires proper patient selection
Inhaled nitrous oxide is not an epidural (TABLE).8 The pain relief is clearly inferior to that of an epidural. Inhaled nitrous oxide will not replace epidurals or even have any effect on the epidural rate at a particular institution.6 However, the use of inhaled nitrous oxide for labor analgesia has a long track record of safety (albeit with moderate efficacy for selected patients) for many years in many countries around the world. Inhaled nitrous oxide is a valuable addition to the options we can offer patients:
- who are poor responders to opioid medication or who have high opioid tolerance
- with certain disorders of coagulation
- with chronic pain or anxiety
- who for other reasons need to consider alternatives or adjuncts to neuraxial analgesia.
Although it is important to be realistic regarding the expectations of analgesia quality offered by this agent,7 compared with other agents we have tried, it has less adverse effects, is economically reasonable, and has no proven impact on neonatal outcomes.
No significant complications with inhaled nitrous oxide have been reported
Systematic reviews did not report any significant complications to either mother or newborn.1,2 Our personal experiences corroborate this, as no complications have been associated with its frequent use at Brigham and Women’s Hospital. Reported adverse effects are mild. The incidence of nausea is 13%, dizziness is 3% to 5%, and drowsiness is 4%; these rates are hard to detect over the baseline rates of those side effects associated with labor and delivery alone.1 Many other centers have now adopted the use of this agent, with several hundred locations now offering inhaled nitrous oxide for labor analgesia in the United States.
Practical use of inhaled nitrous oxide is relatively simple
Several vendors offer portable, user-friendly, cost-effective equipment that is appropriate for labor and delivery use. All devices are structured in demand-valve modality, meaning that the patient must initiate a breath in order to open a valve that allows gas to flow. Cessation of the inspiratory effort closes the valve, thus preventing the free flow of gas into the ambient atmosphere of the room. The devices generally include a tank with nitrous oxide as well as a source of oxygen. Most devices designed for labor and delivery provide a fixed mixture of 50% nitrous oxide and 50% oxygen, with fail-safe mechanisms to allow increased oxygen delivery in the event of failure or depletion of the nitrous supply. All modern, FDA–approved devices include effective scavenging systems, such that expired gases are vented outside (generally via room suction), which prevents occupational exposure to low levels of nitrous oxide.
Inhaled nitrous oxide for labor pain must be patient controlled
An essential feature of the use of inhaled nitrous oxide for labor analgesia is that it must be considered a patient-controlled system. Patients have an option to use either a mask or a mouthpiece, according to their preferences and comfort. The patient must hold the mask or mouthpiece herself; it is neither appropriate nor safe for anyone else, such as a nurse, family member, or labor support personnel, to assist with this task.
Some coordination with the nurse is essential for optimal timing of administration. Onset of a therapeutic level of pain relief is generally 30 to 60 seconds after inhalation has begun, with rapid resolution after cessation of the inhalation. The patient should thus initiate the inspiration of the gas at the earliest signs of onset of a contraction, so as to achieve maximal analgesia at the peak of the contraction. Waiting until the peak of the contraction to initiate inhalation of the nitrous oxide will not provide effective analgesia, yet will result in sedation after the contraction has ended.