Nitrous oxide in early labor. Safety and analgesic efficacy assessed by a double-blind, placebo-controlled study.
BACKGROUND
Intermittent self-administered nitrous oxide has long had widespread use as an analgesic in labor, but its efficacy has not been adequately established. Questions about its effect on maternal oxygenation between labor contractions also have been raised.


METHODS
Twenty-six women were recruited to participate in a randomized, double-blind, cross-over, placebo-controlled study to assess the effect of intermittent nitrous oxide inhalation on labor pain and maternal hemoglobin oxygen saturation (SPO2) during the first stage of labor. Visual analog scale pain scores for each of five consecutive labor contractions were measured after administration of either nitrous oxide or compressed air.


RESULTS
Mean visual analog scale pain scores for five contractions were 5.1, 5.2, 5.7, 5.2, and 5.6 (nitrous oxide) and 4.9, 5.2, 6.1, 5.6, and 5.7 (compressed air). There were no statistically significant differences in pain when nitrous oxide as compared with compressed air was administered. Pain scores did not differ significantly over time as a function of inhaled substance (F = 0.41, P = 0.53). The mean lowest SPO2 observed between these contractions after self-administration of nitrous oxide and air were 97, 97, 97, 97, and 97% (nitrous oxide) and 97, 96, 96, 96, and 96% (compressed air). SPO2 was significantly higher after nitrous oxide administration (F = 8.8, P = 0.007).


CONCLUSIONS
While intermittent self-administered 50% nitrous oxide in oxygen does not appear to predispose parturient women to hemoglobin oxygen desaturation, its analgesic effect has yet to be clearly demonstrated.
Carstoniu
J
J
Department of Anesthesia, Toronto Hospital, Ontario, Canada.
Levytam
S
S
Norman
P
P
Daley
D
D
Katz
J
J
Sandler
A N
AN
D000328:Adult; D016362:Analgesia, Obstetrical; D016058:Analgesia, Patient-Controlled; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007743:Labor, Obstetric; D009609:Nitrous Oxide / Q000008:administration & dosage*; D010100:Oxygen / Q000097:blood; D010147:Pain Measurement; D011247:Pregnancy; D012646:Self Administration
D009609:Nitrous Oxide; D010100:Oxygen