NITROUS-OXIDE IN EARLY LABOR - SAFETY AND ANALGESIC EFFICACY ASSESSEDBY 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 oxygen ation between labor contractions also have been raised. Methods: Twent y-six women were recruited to participate in a randomized, double-blin d, cross-over, placebo-controlled study to assess the effect of interm ittent nitrous oxide inhalation on labor pain and maternal hemoglobin oxygen saturation (Sp(o2)) during the first stage of labor. Visual ana log scale pain scores for each of five consecutive labor contractions were measured after administration of either nitrous oxide or compress ed air. Results: Mean visual analog scale pain scores for five contrac tions were 5.1, 5.2, 5.7, 5.2, and 5.6 (nitrous oxide) and 4.3, 5.2, 6 .1, 5.6, and 5.7 (compressed air). There were no statistically signifi cant differences in pain when nitrous oxide as compared with compresse d 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 low est Sp(o2) observed between these contractions after self-administrati on of nitrous oxide and air were 97, 97, 97, 97, and 97% (nitrous oxid e) and 97, 96, 96, 96, and 96% (compressed air). Sp(o2), was significa ntly higher after nitrous oxide administration (F=8.8, P=0.007). Concl usion: While intermittent self-administered 50% nitrous oxide in oxyge n does not appear to predispose parturient women to hemoglobin oxygen desaturation, its analgesic effect has yet to be clearly demonstrated.