Background: Pain relief during labour is one of the major concerns in obstetrics; severe labor pain causes fear of the next pregnancy, and interferes with the mother's family relationship. 

Objective: The aim of this study was to evaluate the analgesic effects of Entonox during labor on reducing the need for pethidine (Meperidine) and fetal-maternal complications.

Methods: This double-blind randomized clinical trial was conducted on pregnant women who were candidates for vaginal delivery in Educational Hospitals of Mashhad University of Medical Sciences, Iran between January 2014 and November 2015. After entering into the inactive phase of labor, participants were randomly allocated to receive inhaled Entonox gas (n=200) or inhale Oxygen (n=200) as a control group. Mothers inhaled the gas at commencement of pain, and ceased as soon as the pain diminished, up to the end of the second stage of labor which was the neonate's birth. Main outcomes were pain score based on NRS (numerical rating scale), duration of delivery, required pethidine, maternal complications and satisfaction during labour. Chi-square and Independent T-test were used via SPSS for data analysis and P-value less than 0.05 was considered statistically significant.

Results: Four-hundred pregnant women with a mean age of 26.4±5.9 years were studied. Complications such as nausea, vomiting, dizziness, and drowsiness were reported in 25% of the Entonox group and 23% in the control group (p=0.640). Mean of pain severity score during labor in the Entonox and control groups was 4.5±1.2 and 5.2±1.4, respectively (p<0.001). Pethidine requirement, significantly was lower in the Entonox group (31.6±11.8 versus 35.7±12.4; p<0.001). 

Conclusion: In our study, Entonox significantly reduced pain during delivery without significant increase in maternal and neonatal complications. 

Trial registration: The trial is registered at the Iranian Clinical Trial Registry (IRCT.ir) with the IRCT identification number IRCT2015102713159N6. 

Funding: This research has been financially supported by Research Council of Mashhad University of Medical Sciences.


Keywords: Entonox, Analgesia, Obstetrical, Pethidine, Narcotics, Inhalation
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