Influence of Entonox (mixture of 50% nitrous oxide and 50% oxygen) on physiological labor and neonatal outcome in own material

Ginekol Pol. 2022 Jul 27. doi: 10.5603/GP.a2022.0039. Online ahead of print.


Objectives: The aim of the study was to compare delivery and perinatal outcomes with inhaled nitrous oxide to delivery without pain control.

Material and methods: Authors performed retrospective analysis of 260 term deliveries. In the study group (130 women) a mixture of nitrous oxide and oxygen was used. The control group included 130 patients who used no pain relief during delivery.

Results: In nulliparas the pain assessment in 11-points scale was similar in both groups, but the labor was longer (350 ± 152 vs 228 ± 113 minutes; p < 0.001 for the first stage and 46 ± 37 vs 18 ± 18 minutes; p < 0.001 for the second stage), episiotomy incidence was higher (81.4% vs 41.9%; p < 0.001) and perineal laceration lower (2.3% vs 25.7%; p < 0.001) in the study group. In multiparas the pain assessment was lower in the study group (5 vs 7 points; p = 0.006), oxytocin was administered more frequently (45.5% vs 21.4%, p = 0.011), but labor duration was the same in both groups. Episiotomy was more frequent (61.4% vs 37.5%, p = 0.02), but there was no difference in perineal laceration. Apgar score was the same in the study and control group.

Conclusions: We found that Entonox prolongs labor significantly and increases frequency of episiotomy in primiparas with no clear analgesic effect. Offering Entonox to the patients giving birth for the first time is thus questionable. In multiparas it has a good analgesic effect but increases probability of episiotomy with no significant influence on perineal tear, what seems not very high cost of decreased pain related to delivery.

Keywords: analgesic effect; labor; labor pain management; nitrous oxide; pain; pain relief.