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Inhaled Nitrous Oxide Analgesia

Basic Information

Nitrous oxide is an anesthetic gas that is used by anesthesia providers for surgery and by dentists – often referred to as “laughing gas” in those circumstances. Use of nitrous oxide for labor has been very popular in other countries for decades. For example it is used in 40-45% of births in Canada, 65% of births in Sweden, and 50-75% of births in the UK. Until recently it has been used rarely in the United States (currently less than 2% of births). Nitrous oxide does not necessarily decrease pain in the traditional sense but seems to make it easier to manage pain. For example, patients tend to rate their pain with the same number on a pain scale when they do or do not have nitrous but around 75% of patients state that nitrous oxide provided “considerable” or “complete” pain relief.

How is it given?

Nitrous oxide is mixed with oxygen (50% of each) using a bedside machine. A mask is held tightly to your face and you breathe the mixture continuously. To be maximally effective you need to breathe it continuously. Alternatively, if your contractions are absolutely regular in timing you may start breathing it approximately 45 seconds prior to a contraction. The machine will only deliver the nitrous oxide/oxygen mixture if the mask is fitted tightly to your face. You will also need to exhale into the mask so that you are not breathing nitrous oxide into the air in your room. Nitrous oxide is quite safe but must never be used with other sedating or pain medications. It is also important that only you control your mask.

Side effects

The rate of side effects you may experience are approximately:

  • Nausea – 5%
  • Dizziness – 5-10%
  • Dysphoria (“feeling strange”) – 5-10%
  • Drowsiness – 5-20%
  • Hazy memory – 5-10%The rate of serious adverse events is 0.03% and the risk of temporary loss of consciousness is 0.4%.

There are good studies to show that nitrous oxide has no impact on the duration of labor or the mode of delivery (for example – cesarean section, vacuum or forceps assistance, etc).

Impact on baby

Nitrous oxide readily crosses the placenta and within 15 minutes of administration the baby has a blood level that is approximately 80% of yours. However, when used up until the time of birth, the nitrous oxide disappears from the baby’s system within 3 minutes. There are good studies to show that there is no impact of nitrous oxide on the fetal heart rate, your baby’s cord blood gases (a marker of baby’s well-being around the time of birth), or APGAR scores. As far as impact on newborn breathing or neonatal behavioral scores or other neurologic impact there is very little good data to guide us. Studies in animal models being exposed to higher concentrations of nitrous oxide (75% or more) for long periods of time have shown some damage to certain areas of the brain. This is the case with all anesthetic gases and is an area of current investigation. It is unclear if these changes occur in humans and what actual impact they may have. The long use of nitrous oxide in many patients around the world would lead us to believe that it does not cause significant adverse events in the infant central nervous system but we cannot guarantee that with absolute certainty.