Gas kinetics during nitrous oxide analgesia for labour

Anaesthesia. 1996 May;51(5):449-52. doi: 10.1111/j.1365-2044.1996.tb07790.x.


Hypoxaemia may occur after hyperventilation with nitrous oxide during labour. The purpose of this study was to assess whether diffusion hypoxia is a contributory factor. Twenty-four parturients were randomly allocated to receive 50 or 70% nitrous oxide in oxygen. The median nitrous oxide inhalation time per contraction was 58 s and 33 s, respectively. The end-tidal carbon dioxide and the minute ventilation remained unchanged. The end-tidal oxygen concentration was lowest at 120 s, reaching 15.4% in both groups. The oxygen saturation did not differ between the groups with a lowest median value of 96% before the start of nitrous oxide inhalation. Two parturients had episodes of desaturation. Both had low end-tidal oxygen concentrations in association with the desaturation but, as the end-tidal nitrous oxide concentrations were low, the desaturations could not be attributed to diffusion hypoxia.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Analgesia, Obstetrical / adverse effects*
  • Analgesics, Non-Narcotic / administration & dosage
  • Analgesics, Non-Narcotic / adverse effects*
  • Carbon Dioxide / physiology
  • Drug Administration Schedule
  • Female
  • Humans
  • Hypoxia / chemically induced*
  • Kinetics
  • Nitrous Oxide / administration & dosage
  • Nitrous Oxide / adverse effects*
  • Oxygen / physiology
  • Pregnancy


  • Analgesics, Non-Narcotic
  • Carbon Dioxide
  • Nitrous Oxide
  • Oxygen