Comparison of the Mean Duration of Active Phase of Labor Using Entonox Inhalation and Placebo

Delivery is an active process that causes one of the most severe pains that a woman experiences in her life. Today, pain control methods, such as using Entonox (N2O + O2), have been suggested to reduce the pain of the active phase of labor. This study was conducted with the aim of comparing the mean duration of the active phase of labor using Entonox and placebo. In this clinical trial study, 120 pregnant women with classes 1 and 2 of American Society of Anesthesiologists (ASA), in the active phase or cervical dilatation of 4 cm, and the gestational age of 37-41 weeks were randomly divided into two equal groups of Entonox inhalation and placebo (compressed air). The duration of delivery in dilates 4 to 6, 6 to 8, and 8 to 10 cm, and finally the total active phase time in the two groups were assessed and compared. The duration of active phase of labor in the Entonox group (201.6 ± 49.2 minutes) was significantly less than placebo group (252.6 ± 62.4 minutes) (P < 0.05). Moreover, the duration of dilation was 4 to 6 and 6 to 8 cm in the Entonox group, and was significantly less than placebo group (P < 0.05); but there was no significant difference between the groups in terms of dilation of 8 to 10 cm (P = 0.35). Using inhalation of Entonox in comparison with the placebo, decreased pain and the duration of active phase of labor, especially in the first stages of this phase.