Inhaled Analgesia Seems Effective for Early Labor

September 11, 2012 — Inhaled pain relief is effective during early labor, according to a systematic review of studies examining the efficacy of inhaling oxygen with either nitrous oxide or a flurane derivative, published online September 11 in the Cochrane Database of Systematic Reviews.

For women who wish to avoid invasive pain control during labor, self-administered inhaled analgesia is an attractive alternative because it can be administered fast and acts quickly. Midwives can set up nitrous oxide, but the gas may case nausea, vomiting, dizziness, and drowsiness. Fluranes offer stronger anaesthesia with lower incidence of adverse effects, but initial administration requires supervision by an anesthesiologist. With both forms of inhaled anaesthesia, women remain awake and able to swallow.

Trudy Klomp, MSc, from the Department of Midwifery Science and the EMGO Institute for Health and Care Research at VU University Medical Center in Amsterdam, the Netherlands, and colleagues analyzed data from 26 studies involving 2959 women who had participated in trials evaluating inhaled pain relief during early labor.

Sample sizes ranged from 18 to 509 patients, and the studies were conducted in the United States, United Kingdom, Sweden, Norway, Canada, China, Iran, and Singapore. Combining data from the trials reviewed, the researchers measured pain relief and pain intensity with a visual analog scale ranging from 0 to 100 mm (ie, from none to worst pain). The studies were heterogeneous: comparing nitrous oxide to a flurane, evaluating different strengths or delivery methods of either type of analgesic, or comparing inhaled analgesics to placebo, nothing, or transcutaneous electrical nerve stimulation (TENS).

Flurane derivatives were superior to nitrous oxide, offering lower pain intensity (average mean difference, 14.39; 95% confidence interval [CI], 4.41 - 24.37 among 70 women in 3 studies) and higher pain relief (average mean difference, −16.32; 95% CI, −26.85 to −5.79 among 70 women participating in 2 studies). The researchers caution, however, that the cross-overs in some of the trials were of "questionable design."

Nitrous oxide relieved pain more effectively than either placebo or no treatment (average relative risk 0.06; 95% CI, 0.01 - 0.34 among 310 women in 2 studies; average mean difference, −3.50; 95% CI, −3.75 to −3.25 according to a study of 509 women). Strength of analgesia, delivery method, or using TENS instead of inhalation had no effect on outcomes.

The finding of the efficacy of inhaled analgesia is important, the researchers write, because many women in labor do not experience adequate pain control. "Even in hospitals with full-time obstetric anaesthesia coverage, no one may be available to place an epidural, provide another highly effective method of labour analgesia, or provide a labour-intensive non-pharmacological method to help the woman in pain," the researchers write.

The authors cite several limitations to the analysis, including the small size of some studies, the subjectivity of perception of pain intensity, and different evaluations of pain in different studies.

"Despite limitations...the statistically significant results for reduction in pain intensity and increase in pain relief indicates that inhaled analgesia may be a useful form of pain management for some women in labour," the authors conclude. "Inhaled analgesia may be beneficial for those women in labour who want to have some form of pharmacological pain relief, without invasive methods. It was not possible to draw any conclusions in relation to poorer outcomes for the newborns or the mothers due to a paucity of evidence."

The researchers suggest that further trials with adequate power be conducted to determine which anesthetic provides women with a greater feeling of control during labor, offers more satisfaction with the birth process, and eases breast-feeding. The studies that were evaluated did not consider these outcomes.

The authors have disclosed no relevant financial relationships.

Cochrane Database Syst Rev. Published online September 12, 2012. Abstract