Improving Labour Induction Analgesia: a Randomized Control Trial of Single Epidural Fentanyl Bolus at Epidural Initiation for Induction of Labour

The pain felt during labour is influenced by many physiological and psychosocial factors and often requires some form of relief. Pain can be intensified for labour inductions as the body's natural pain-relieving endorphins are not readily released in response to the increasingly strong and painful uterine contractions- leading to earlier and more frequent requests for analgesia. Induced labour has also been reported as being significantly longer than spontaneous labour. Current evidence suggests that epidural, combined spinal epidural and inhaled analgesia effectively manage pain in labour, but may give rise to adverse effects for both the mother and neonate. Despite this, epidural analgesia is considered the gold standard in the treatment of labor pain and has a role in labour inductions. Opioids are often added to epidurals to improve the quality of analgesia because of their faster onset and superior pain relief. When combined with opioids, lower concentrations of local anesthetic are needed. Such combinations provide adequate analgesic effect while allowing the parturient to maintain maximal motor function.

In studies assessing the safety and efficacy of labour analgesia, neonatal outcome is a primary concern and the use of opioids for labour analgesia is controversial because of the potentially negative effects on neonates. Common indicators of poor neonatal outcomes include a lower Apgar score, a lower Neurological and Adaptive Capacity Score (NACS), and a lower umbilical artery or vein pH value.

Fentanyl is the most widely investigated adjuncts to epidural local anesthetics. Various RCTs comparing epidural local anesthetics with and without fentanyl have found no significant differences in neonatal Apgar scores at one and five minutes between the groups. A recent meta-analysis of twenty-one RCTs involving epidural Fentanyl and Sufentanil concluded that there was no difference in the incidence of Apgar scores < 7 at one and five minutes, no significant differences in the NACS at two hours and at 24 hours, and no significant differences were found in umbilical cord artery pH between the epidural opioid and control groups. This meta-analysis concluded that the common doses of Fentanyl (total dose of 100-500 mcg) and Sufentanil (total dose of 7.5-30 mcg) used with an epidural/spinal technique are safe for neonates up to 24 hours after delivery. Despite reassuring findings regarding epidural opioids, other investigators have found an association between epidural opioids and neonatal respiratory distress and the use of epidural fentanyl has been associated with a NACS that failed to improve by 24 hours in one study. Furthermore, the use of epidural opioids was associated with reduced rates of breastfeeding in some observational studies, but evidence is unclear and debated.

Given the heightened implications for the mother and neonate in situations requiring induction of labour, the desire for a positive outcome whilst still providing adequate maternal analgesia is paramount. This study thus aims to investigate whether a preliminary epidural Fentanyl bolus at the initiation of the epidural may help to improve analgesia for women undergoing labour inductions for post-term pregnancy in a safe manner. Importantly, the main rationale of this proposed practice being that by achieving adequate epidural analgesia earlier in the labour induction, this may lead to better pain control overall and less overall requirements for epidural PCEA boluses and epidural "top-ups" as the induction progresses.