Timing of intravenous patient-controlled remifentanil bolus during early labour

Remifentanil labour analgesia is superior to nitrous oxide but less potent than epidural analgesia. The short onset and offset times of effect suggest that the timing of the bolus in the contraction cycle could have importance. We hypothesised that administering a remifentanil bolus during contraction pause would improve analgesia in early labour.

With permission from the ethical committee and the National Authority of Medicines, 50 parturients with uncomplicated singleton pregnancies and informed consent participated in a double blind cross-over study. Intravenous doses of 0.4 μg/kg remifentanil with 1-min infusion times were used during two study periods lasting six to eight contractions. Remifentanil and saline syringes were attached to two patient-controlled devices, one of which administered the bolus immediately after a trigger and the other targeted to start 140 s before the next contraction. The parturients assessed contraction pain, pain relief, sedation and nausea. Oxygen saturation (SaO(2)) pulse and blood pressure were recorded. SaO(2)<95% was the indication for oxygen supplement.

Forty-one parturients were included in the analyses. Because of the period effect, pain and pain relief scores were analysed separately for each of the study periods. The mean pain and pain relief scores were similar during the two different dosing regimens. Side effects, the need for supplemental oxygen, SaO(2) and haemodynamics were similar. In a subgroup with long and regular contractions, however, delayed boluses were associated with lower pain scores.

Administering a remifentanil bolus during the uterine contraction pause does not improve pain relief.