Inhaled analgesia for relieving pain during labour

Labour pain and methods to relieve it are major concerns for pregnant women, healthcare workers and the general public. These concerns have implications for the course of labour, for the quality of maternal and infant outcomes as well as for the costs of obstetric health care.

Women in labour who need pain relief should not only have access to invasive methods such as an epidural, which may have considerable side effects, but other means of pain relief as well. Futhermore, even in hospitals with full-time obstetric anaesthesia coverage no one may be available to give an epidural, and in primary care, invasive methods for pain relief are not available at all.

All women in labour should have the opportunity to choose some non-invasive method of relatively effective and safe analgesia at short notice when they wish it during labour. Inhaled pain relief, such as nitrous oxide and some flurane derivatives, may be a very useful additional method for pain relief. It is relatively easy to administer, can be started in less than a minute, and become effective within a minute. Nitrous oxide is more widely known and used as inhaled pain relief during labour compared to flurane derivatives, probably due to the availability of safe equipment, no pungent smell and the ease of administration.

In this review of 26 randomised controlled trials of 2959 women, the effectiveness and safety of inhaled analgesia as pain relief for women in labour were studied. It was found that inhaled analgesia may help relieve pain during labour but women have to be informed about the side effects, such as nausea, vomiting, dizziness and drowsiness.

Inhaled analgesia may help relieve labour pain without adversely increasing operative delivery rates (forceps or vacuum extraction, caesarian section), or affecting neonatal well being. Flurane derivatives were found to be slightly more effective than nitrous oxide for the reduction of pain and for pain relief although nitrous oxide also helped to relieve pain when compared with no treatment.

Women who used nitrous oxide were more likely to experience nausea compared with flurane derivatives. When nitrous oxide was compared with no treatment or placebo, nitrous oxide resulted in side effects such as nausea, vomiting, dizziness and drowsiness.

There was no information for satisfaction with childbirth experience or sense of control in labour in these studies and further research on these two important outcomes would be helpful.

Authors' conclusions: 

Inhaled analgesia appears to be effective in reducing pain intensity and in giving pain relief in labour. However, substantial heterogeneity was detected for pain intensity. Furthermore, nitrous oxide appears to result in more side effects compared with flurane derivatives. Flurane derivatives result in more drowsiness when compared with nitrous oxide. When inhaled analgesia is compared with no treatment or placebo, nitrous oxide appears to result in even more side effects such as nausea, vomiting, dizziness and drowsiness. There is no evidence for differences for any of the outcomes comparing one strength verus a different strength of inhaled analgesia, comparing different delivery systems or comparing inhaled analgesia with TENS.

Read the full abstract...

Many women would like to have a choice in pain relief during labour and also would like to avoid invasive methods of pain management in labour. Inhaled analgesia during labour involves the self-administered inhalation of sub-anaesthetic concentrations of agents while the mother remains awake and her protective laryngeal reflexes remain intact. Most of the agents are easy to administer, can be started in less than a minute and become effective within a minute.


To examine the effects of all modalities of inhaled analgesia on the mother and the newborn for mothers who planned to have a vaginal delivery.

Search strategy: 

We searched the Cochrane Pregnancy and Childbirth Group’s Trials Register (31 January 2012),, and Current Controlled Trials (2 June 2012), handsearched conference proceedings from the American Society of Clinical Anesthesia (from 1990 to 2011), contacted content experts and trialists and searched reference lists of retrieved studies.

Selection criteria: 

Randomised controlled trials comparing inhaled analgesia with other inhaled analgesia or placebo or no treatment or other methods of non-pharmacological pain management in labour.

Data collection and analysis: 

Review authors independently assessed trials for eligibility, methodological quality and extracted all data. Data were double checked for accuracy.

Main results: 

Twenty-six studies, randomising 2959 women, were included in this review.

Inhaled analgesia versus a different type of inhaled analgesia
Pain relief was measured using a Visual Analogue Scale (VAS) from 0 to 100 mm where 100 corresponds to the most relief. Pain intensity was measured using a VAS from 0 to 100 mm, where 0 corresponds to no pain at all and 100 corresponds to the worst pain. The highest score for pain relief is the most positive in contrast to 'pain intensity' in which the higher score is more negative.

Flurane derivatives were found to offer better pain relief than nitrous oxide in first stage of labour as measured by a lower pain intensity score (average mean difference (MD) 14.39, 95% confidence interval (CI) 4.41 to 24.37, three studies, 70 women), also a higher pain relief score for flurane derivatives compared with nitrous oxide (average MD -16.32, 95% CI -26.85 to -5.79, two studies, 70 women). Substantial heterogeneity was found in the analyses of pain intensity (P = 0.003) and in the analysis of pain relief (P = 0.002).These findings should be considered with caution because of the questionable design of the included cross-over trials. More nausea was found in the nitrous oxide group compared with the flurane derivatives group (risk ratio (RR) 6.60 95% CI 1.85 to 23.52, two studies, 98 women).

Inhaled analgesia versus placebo or no treatment
Placebo or no treatment was found to offer less pain relief compared to nitrous oxide (average RR 0.06, 95% CI 0.01 to 0.34, two studies, 310 women; MD -3.50, 95% CI -3.75 to -3.25, one study, 509 women). However, nitrous oxide resulted in more side effects for women such as nausea (RR 43.10, 95% CI 2.63 to 706.74, one study, 509 women), vomiting (RR 9.05, 95% CI 1.18 to 69.32, two studies, 619 women), dizziness (RR 113.98, 95% CI 7.09 to 1833.69, one study, 509 women) and drowsiness (RR 77.59, 95% CI 4.80 to 1254.96, one study, 509 women) when compared with placebo or no treatment.

There were no significant differences found for any of the outcomes in the studies comparing one strength versus a different strength of inhaled analgesia, in studies comparing different delivery systems or in the study comparing inhaled analgesia with TENS.

Due to lack of data, the following outcomes were not analysed within the review: sense of control; satisfaction with childbirth experience; effect on mother/baby interaction; breastfeeding; admission to special care baby unit; poor infant outcomes at long-term follow-up; or costs.