An Investigation into the Side Effects of Entonox on Primiparas in Painless Labor

Introduction: Labor pain causes a great fear of vaginal delivery as well as increase of cesarean section among women. Therefore, using harmless and efficacious pain relief methods is of great significance. Entonox is an effective and popular method for labor pain relief. However, there is a dearth of research conducted to examine its efficacy and side effects. Objectives: Accordingly, the present study aimed at investigating the side effects of nitrous oxide on the mother and fetus. Patients and Methods: This is a randomized controlled trial [RCT] study carried out on 178 primipara candidates for natural. During the active labor phase, women were assigned to two groups: intervention group [89 women inhaling Entonox] and control group [89 women inhaling oxygen]. In addition, the required data including age, gestational age, evidence of abruption, mode of delivery, meconium staining, fetal Apgar score, side effects of drug consumption, the amount of postpartum bleeding, initial hemoglobin concentration, and its concentration 6 hours after delivery were recorded. Then, the data were analyzed in SPSS software, version 16, using t-student, and Chi-square tests. Results: There was no significant difference between the two groups in terms of the evidence of abruption, accelerated labor, meconium staining by the fetus, mean Apgar scores at 1 and 5 min and the final mode of delivery [P > 0.05]. Side effects such as dizziness, dry mouth, numbness of the tongue, nausea, and drowsiness were reported in the group inhaling Entonox. In the two modes of vaginal delivery and cesarean section, the mean reduction in hemoglobin concentration 6 hours postpartum in the group inhaling Entonox was less than that of the control group and the difference was significant [P < 0.05]. Conclusion: Compared to the use of oxygen, the use of Entonox gas for painless labor did not cause adverse effects on the mother and fetus; however, only minor side effects including drowsiness, dry mouth, dizziness and nausea, and numbness of the tongue were observed. Furthermore, it was observed that Entonox caused less reduction in hemoglobin concentration of the mother which might be related to its positive effects on labor progress and its duration. Keywords: labor, pain, Entonox, oxygen