50% nitrous oxide will provide satisfactory analgesia in some women undergoing vaginal delivery, and is insufficient to cause respiratory depression or significantly impair airway reflexes [Stoelting RK. Basics of Anesthesia, 5th ed. Elsevier (China) p. 489, 2007]. A Chinese study (only English abstract is available) of 1300 women comparing 50% nitrous oxide to oxygen showed better pain control, lower rate of Cesarean section, shorter active phase of labor, an no differences in neonatal Apgar scores or blood gas values [Su F et al. Zhonghua Fu Chan Ke Za Zhi 37: 584, 2002]. Sub-anesthetic desflurane, when compared to nitrous oxide in a smaller, less-comprehensive study, was shown to have comparable analgesic effects [Abboud TK et al. Acta Anaesthesiol Scand 39: 259, 1995]. Both drugs should be used with caution if placental compromise is suspected – a small study from Sweden showed that while nitrous oxide was effective as analgesic, the degree of analgesia was proportional to the degree of cardiac depression [Westling F et al. Acta Anaesthesiol Scand 36: 175, 1992]. Nitroglycerin should be available for uterine relaxation in any woman undergoing a vaginal delivery.