Background. Entonox (N2O2) which is an inhalational gas for relieving labor pain is commonly used intermittently; however some women are interested in continuous breathing in face mask. So we decided to compare the complications induced by two methods to find out whether it is safe to permit the mothers to use Entonox continuously or not. Patients and Methods. This randomized clinical trial was performed in Mobini Hospital, Sabzevar, Iran. 50 parturients used Entonox intermittently and 50 cases used it continuously during labor. Then obstetrical outcomes were analyzed in two groups by spss 17 software, -test, and Chi2 while was considered significant. Results. This study showed the mean duration of second stage of labor had no significant difference (). Perineal laceration was less in continuous group significantly (). Assisted vaginal birth was not different significantly (). Uterine atony had no significant difference in two groups (). Maternal collaboration in pushing and satisfaction were higher in continuous group significantly (), (). Apgar score of neonates at first and fifth minute was acceptable and not different significantly in two groups (). Conclusions. Our study demonstrated continuous method is also safe. So, it seems reasonable to set mothers free to choose the desired method of Entonox usage. 1. Introduction Over many centuries human has always persued finding a harmless way to relieve labor pain. Many methods have been used for this purpose; some of them constitute nonpharmaceutical methods such as relaxation therapy and others are applied by pharmaceutical agents [1]. Severity of labor pain depends on some factors such as psychological background of mother, size and presentation of fetus, whether labor is spontaneous or augmented, and rate of cervical dilatation in first stage [2]. Indeed, severe pain associated with maternal anxiety can lead to maternal exhaustion, frustration, and inability to push in terminal stages of labor. This process in addition to fetal damage can lead to maternal complications such as perineal lacerations, uterine atony, uterine rupture, and even maternal death [1–3]. Numerous methods are administered for decreasing labor pain. Gas inhalation is an old method which was firstly applied in the eighteenth century. By gradual development, Minitt invented a self-administrable machine for relieving pain in 1934. Entonox which is a composition of 50% N2O and 50% O2 compacted in cylindric containers was commercially introduced in 1961. During last decades, Entonox has gained considerable acceptance in many European
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