Gas kinetics during nitrous oxide analgesia for labour.
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.
Einarsson
S
S
Department of Anaesthesia and Intensive Care, Sahlgrenska University Hospital, Göteborg, Sweden.
Stenqvist
O
O
Bengtsson
A
A
Norén
H
H
Bengtson
J P
JP
D000328:Adult; D016362:Analgesia, Obstetrical / Q000009:adverse effects*; D018712:Analgesics, Non-Narcotic / Q000008:administration & dosage / Q000009:adverse effects*; D002245:Carbon Dioxide / Q000502:physiology; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000139:chemically induced*; D007700:Kinetics; D009609:Nitrous Oxide / Q000008:administration & dosage / Q000009:adverse effects*; D010100:Oxygen / Q000502:physiology; D011247:Pregnancy
D018712:Analgesics, Non-Narcotic; D002245:Carbon Dioxide; D009609:Nitrous Oxide; D010100:Oxygen