A Randomized Controlled Trial Comparing Use of Enthonox With Pethidine for Pain Relief in Primigravid Women During the Active Phase of Labor

BACKGROUND The use of pain-relieving drugs during labor is now part of standard care in many countries throughout the world. Each method of pain relief has its own risks and benefits, variations in effectiveness, and availability and acceptability. OBJECTIVES This study aimed to assess the efficacy and safety of intramuscular pethidine as an analgesic during labor by comparing it to inhaled 50% nitrous oxide (Entonox). METHODS In this clinical trial study, 100 women who expected to have a natural childbirth were observed. The inclusion criteria for this study were the commencement of spontaneous labor pain along with appropriate maternal and fetal indications for vaginal delivery. By using random numbers, each subject was randomly allocated to one of two groups, with one group using Entonox and the other receiving an intramuscular injection of 0.5 mg/kg of pethidine for pain relief. The intensity of labor pain experienced by the subjects and the outcomes of the deliveries were collected with questionnaires. RESULTS The average pain scores in the Entonox and pethidine groups were 3.94 ± 1.4 and 5.6 ± 1.1, respectively, 30 minutes after intervention (P = 0.001), but there was not a significant difference in the severity of the pain (5.06 ± 1.4 and 4.7 ± 1.1 for the Entonox and pethidine groups, respectively) between the subjects in each group 60 minutes after the intervention (P = 0.592). No significant differences were seen in the duration and interval of uterine contractions, maternal complications, Apgar scores, and the duration of the first and second stage of labor between the two studied groups (P > 0.05). An analysis of the pooled risk differences showed that none of the side effects investigated were significantly different between the two groups except for mouth dryness, which was significantly higher in nitrous oxide users (P = 0.044). CONCLUSIONS Inhaled nitrous oxide seems to give better pain relief in the short term compared to a single dose of pethidine. Entonox, which is more convenient to administer than an intramuscular injection of pethidine, is also regarded as safe both for mothers and neonates.