Background: Systemic opioids are widely used for relief of labor pain. Self-administered nitrous oxide with concentration of 50% is a new form of analgesia. The aim of this study was to compare the analgesic efficacy and side effects of patient controlled, inhaled nitrous oxide 50% ''Entonox'' with systemic intramuscular pethidine, in reducing of pain during normal vaginal labor in Iranian population. Materials and Methods:In a randomized controlled study the analgesic efficacy of inhaled 50% nitrous oxide (Entonox) was evaluated compared to intra muscular pethidine for reducing labor pain among 100 women undergoing normal vaginal delivery.Results: Mean maternal age was 26.2 and 27.2 years in Entonox and Pethidine groups, respectively. Duration of first and second stages was significantly shorter in patients receiving nitrous oxide as analgesia, comparing to pethidine group (P<0.05). Pain severity according to VAS score was significantly lower in patient received nitrous oxide (P=0.0001). We also showed significantly higher satisfaction of pain reduction in nitrous oxide group during labor (P=0.01). No significant different was observed among the groups regarding infant complications. Conclusion:Although nitrous oxide is certainly not a potent analgesic, we found that it has more beneficial effects than pethidine in parturient women which remains to be cleared.

Systemic opioids are widely used for the relief of labor pain. Self-administered nitrous oxide with concentration of 50% is a new form of analgesia. The aim of this study was to compare the analgesic efficacy and side effects of the patient controlled inhaled nitrous oxide (50% ''Entonox'') with systemic intramuscular pethidine, in reducing pain during normal vaginal labor in Iranian population. In a randomized controlled study, the analgesic efficacy of inhaled 50% nitrous oxide (Entonox) was evaluated as compared to intra muscular pethidine for reducing labor pain among 100 women undergoing normal vaginal delivery. Mean maternal age was 26.2 and 27.2 years in entonox and pethidine groups, respectively. Duration of first and second stages was significantly shorter in patients receiving nitrous oxide as analgesia as compared to pethidine group (P < 0.05). Pain severity according to visual analog scale (VAS) score was significantly lower in patient that received nitrous oxide (P = 0.0001). We also showed significantly higher satisfaction of pain reduction in nitrous oxide group during labor (P = 0.01). No significant difference was observed among the groups regarding neonatal complications. Although, nitrous oxide is certainly not a potent analgesic, we found that it has more beneficial effects than pethidine in parturient women which is yet to be cleared.

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