Entonox for labor pain: a randomized placebo controlled trial

Abstract

This study aims to investigate the effectiveness of nitrous oxide on pain of labor contractions and on maternal SaO2. The patients were randomized to receive either a pre-prepared mixture of 50% nitrous oxide and oxygen or 50% oxygen by a coin. Study drugs started as early as the onset of pain with each contraction. The patient herself administered gases via a facemask connected to the uni-directional valve which enables the patients to breathe fresh gas in each inspiration. The gas administration was continued to the end of contraction pain at which the patient breathed the room air. Variables such as SaO2, blood pressure, pain and side effects were recorded. 534 ASA I and II parturients, aged from 16 to 35 years, scheduled for elective labor from September 2004 to 2006 were evaluated. Four patients were lost from the study. The mean age of patients was 25.5+/-4.3 years. During the first three measurements, the SaO2 was significantly higher in control group. In addition, the mean arterial pressure was comparable between groups except two first measurements in which the control group was higher. All the Visual Analogue Scale (VAS) values were significantly lower in nitrous oxide group. There were no significant differences in 1st and 5th min apgar scores between groups. All of the side effects were significantly higher among patients in nitrous oxide. In conclusion, our data indicate that using nitrous oxide 50% provides significant pain relief. Nonetheless, it is associated with few side effects, nitrous oxide can be quickly implemented during advanced painful labor.