Does Induction or Augmentation of Labor Affect the Analgesic Efficacy of Intrathecal Opioids?: A Retrospective Cohort Study

Background. Induction or augmentation of labor may cause more painful contractions compared to spontaneous labor and pose a challenge to the efficacy of analgesia provided by spinal opioids alone in the early phase of labor. Therefore, we studied the analgesic efficacy and maternal satisfaction during spontaneous and artificially induced or augmented delivery in parturients receiving neuraxial analgesia with intrathecal opioids. Methods. A forty-parturient cohort that received intrathecal opioid (sufentanil 5 mu g or fentanyl 20 mu g) by the combined spinal-epidural method at an early phase of labor (cervical dilatation <= 5 cm) was used for this post hoc study. Maternal satisfaction and pain during contractions were measured on 0-100 visual analog scale at 30 minutes after the initiation of labor analgesia. Obstetric parameters (methods used to advance labor, cervical dilatation, use of oxytocin, effective time of spinal opioids, and labor outcome) were also measured. Results. Of the 40 parturients, 18 had spontaneous labor and 22 had induced or augmented labor (prior cervical dilatation, artificial rupture of membranes, or oxytocin infusion at the time of neuraxial analgesia initiation). Spontaneous labor associated with lower mean pain scores (6.4 (+/- 12.8) vs 29.6 (+/- 30.6) mm, P=0.005) and higher satisfaction scores (96.9 (+/- 5.3) vs 81.1 (+/- 28.0) mm, P=0.024) compared to induced or oxytocin augmented labor at 30 minutes after the initiation of analgesia. The parturients were at a similar stage of labor, and their labor progressed at a similar rate. Conclusions. In parturients undergoing nonspontaneous labor, the initiation of labor analgesia by intrathecal opioids alone may not be sufficient for adequate analgesia and either intrathecal or epidural analgesia with a mixture of opioid and local anesthetic should be considered in this population. This trial is registered with NCT02885350.