Nitrous oxide for analgesia in external cephalic version at term: prospective comparative study

Objective: The objective of this study was to analyze the effect of using inhaled nitrous oxide (N2O) for analgesia in external cephalic version (ECV) at term on the success rate of the procedure, on pain, and on obstetric and perinatal outcomes. Methods: A prospective comparative cohort study among 300 women with singleton pregnancy in breech presentation at term undergoing an ECV with inhaled N2O in a 50: 50 mix with oxygen for analgesia and 150 ECVs with no analgesia. Results: The success rate was 52.3% in the N2O cohort and 52.7% in the controls (P=0.94), whereas the median level of pain was statistically lower in women given N2O (median, 6; range, 4-7, vs. median, 7; range, 5-8; P<0.01). This improvement is mainly from a 49% decrease in severe pain. There were no significant differences in the rate of complications associated with the ECV, in the rate of cesarean sections, or in perinatal outcomes. Furthermore, there were no severe complications secondary to N2O inhalation. Conclusions: N2O inhalation at a concentration of 50% for analgesia during ECV decreases the level of severe pain experienced by women, appears to be safe both for mother and child, and has no influence on the success rate of ECV or the perinatal outcomes.