Does the use of low dose bupivacaine/opioid epidural infusion increase the normal delivery rate?

Abstract

To investigate whether using low dose epidural infusion improves the normal delivery rate, outcome of labour was studied in women with singleton vertex presentations randomised to receive either 0.0625% bupivacaine opioid, or plain bupivacaine 0.125% for labour. The infusion rate was titrated to maintain analgesia and a sensory level to T10. Data were analysed using the unpaired t test, Mann–Whitney U test and for categorical variables χ² test. Adjusted odds ratios for factors significantly associated with non-normal delivery were calculated using stepwise logistic regression. There were 291 women in the low dose and 296 in the plain bupivacaine group. There were no significant differences between groups in parity, race, induction of labour, use of augmentation, cervical dilatation at epidural insertion, duration of any stage of labour or duration or volume of infusion. Total dose of bupivacaine (126±47 mg versus 91±32 mg) and the proportion of women with motor block at the end of labour (45% versus 27%) were significantly greater in the plain bupivacaine than in the low dose group (P<0.0001). The adjusted odds ratios (95% CI) for factors significantly associated with non-normal delivery were primiparity: 4.68 (2.78–7.88), older maternal age: 1.1 (1.05–1.14), longer active second stage of labour: 1.01 (1.005–1.017), total bupivacaine dose: 1.01 (1.005–1.016) and greater cervical dilatation at epidural insertion 1.22 (1.08–1.37). Treatment group and motor block at the end of labour had no significant effect. We found no increase in normal delivery rate with low dose infusions.

Introduction

The effect of epidural analgesia during labour on delivery type has long been the subject of discussion. In the 1960s and 70s a possible increase in the forceps rate was the focus of attention, though a causal association was disputed by Doughty¹ who was prone to point out that it was not epidurals but obstetricians who applied the forceps. In the 1980s, though sundry observational studies noted the inevitable link between epidurals and obstetric intervention,[2], [3] any causal association was refuted by a good impact study showing no overall increase in abnormal deliveries in an obstetric population after the introduction of an extensive epidural service.⁴ In North America, concern related to the increasing caesarean section rate, and epidural analgesia was one of the scapegoats.⁵ Now, numerous randomised controlled trials and several meta-analyses[6], [7], [8] comparing epidural with systemic analgesia have refuted any causal relationship between epidural analgesia and the caesarean section rate. Nevertheless, epidural analgesia is associated with an increased duration of the second, and possibly the first, stage of labour, and an increased instrumental delivery rate.⁶

It has been assumed that the introduction of low dose local anaesthetic/opioid combinations, in reducing motor block and complete numbness, would mitigate this effect, although the evidence is conflicting.⁹ Publication of results of the COMET trial,¹⁰ which supported the assumption, stimulated us to reconsider our own data. During the years 1991–1995, 602 women who requested epidural analgesia for labour at St. Thomas’ Hospital were randomised to receive infusions of either low dose local anaesthetic/opioid combinations or plain bupivacaine. The primary purposes of these randomised controlled trials were to study the effect of the low-dose combination on motor block and long-term backache,[11], [12] and on oxygenation¹³ and gastric emptying¹⁴ in the mother, and Apgar score, acid–base status, neurologic and adaptive capacity score (NACS) [11], [13], [14] and respiration¹⁵ in the newborn. In all the trials inclusion criteria and epidural management were similar and a secondary purpose was to document delivery type, which was recorded prospectively throughout the studies. By analysis of data from woman who had singleton vertex presentations among our total randomised population, we therefore sought to discover whether there was a difference in obstetric outcome between the two treatment groups.