Comparison of remifentanil and nitrous oxide in labour analgesia

Background:  We compared the efficacy and side-effects of remifentanil with those of nitrous oxide during the first stage of labour. Methods:  Twenty parturients participated in a randomized, double-blind, cross-over study. Intravenous remifentanil in 0.4 µg kg−1 PCA doses with 1-min infusion and lock-out times and intermittent inhaled 50% nitrous oxide were compared during 20-min study periods with a 20-min wash-out sequence after each period. The parturients assessed the intensity of contraction pain (verbal numerical score 0–10), pain relief (score 0–4) and side-effects every 10 min. Noninvasive blood pressure, heart rate (HR), oxyhaemoglobin saturation (SaO2), end-tidal carbon dioxide, fractions of inhaled and exhaled oxygen and nitrous oxide and foetal heart rate (FHR) were recorded. Hypoxaemia and bradycardia were defined as SaO2<90% and HR<50, respectively. Results:  Fifteen parturients completed the study. There was no period effect or treatment-period interaction. The median decrease in pain score for remifentanil was 1.5 and that for nitrous oxide 0.5 (P=0.01). The parturients gave better pain relief scores with remifentanil than with nitrous oxide (median 2.5 vs. 0.5, respectively, P<0.001). Sedation was reported more often, and SaO2 was slightly lower during remifentanil administration. No episodes of hypoxaemia occurred. There was no difference in maternal blood pressure and HR or the incidence of abnormal FHR during remifentanil compared to nitrous oxide. Most parturients preferred remifentanil to nitrous oxide (14 vs. 1, P<0.001). Conclusions:  This study suggests that IVPCA remifentanil provides better labour analgesia than intermittently inhaled nitrous oxide.