ArticlesEffect of low-dose mobile versus traditional epidural techniques on mode of delivery: a randomised controlled trial
Introduction
Epidural analgesia is used for pain relief in labour by more than 150 000 women every year in the UK, and many more worldwide.1, 2 It is the most effective form of pain relief during labour but is associated with increased rates of instrumental vaginal delivery, prolonged labour, and oxytocin augmentation.3 Epidural analgesia does not seem to affect the likelihood of caesarean section delivery.3 Findings that show adverse effects are from trials based on traditional epidural analgesia, which usually results in dense paralysis of motor functions (ie, block). Some of the adverse events might be related to this motor paralysis, which can affect pelvic floor tone, mobility, and ability to push during labour.
New forms of epidural analgesia use combinations of opioid and less concentrated local anaesthetic which preserves maternal motor function, and allow parturients to walk about. However, these low-dose epidurals are used only in a minority of units.2
Although low-dose techniques have been associated with increased maternal satisfaction,4, 5 effects on obstetric outcome are uncertain. Nageotte and colleagues6 in the USA showed a reduction in instrumental vaginal delivery rate with a combined spinal epidural—a technique that is more controversial in the UK.7 They studied nulliparous women who had spontaneous labour at full term. Women in spontaneous labour are much less likely to receive epidural because those who are induced have long labours and therefore request analgesia more often. Several low-dose epidural techniques are available, which might have a differential effect on paralysis of motor functions. For example, continuous infusion, a commonly used technique,2 is associated with a higher total dose of local anaesthetic than intermittent anaesthetic top-ups, to achieve equivalent analgesia.
We did a randomised controlled trial (Comparative Obstetric Mobile Epidural Trial, COMET), to compare traditional epidural analgesia for labour with two types of low-dose techniques—combined spinal and continuous infusion.
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Patients
Our study population included all nulliparous women who requested epidural for pain relief during labour in two maternity units between Aug 1, 1997, and April 30, 2000. The exclusion criteria were: contraindication to epidural analgesia, previous epidural or spinal procedure, imminent delivery, or injection of pethidine within the previous 4 h. All nulliparous women who had planned to deliver at each unit were sent a study information leaflet and questionnaire about pregnancy symptoms and
Results
We enrolled 1054 nulliparous women requesting epidural for pain relief to the COMET2 sample, a 55% recruitment rate from eligible women (figure). The most common reason for non-recruitment was that women were not asked to take part in the trial by the duty anaesthetist. 353 women were randomly assigned to traditional, 351 to combined spinal, and 350 to low-dose infusion group and almost all received their allocated technique. 16 (2%) women delivered before the epidural could be inserted and six
Discussion
Low-dose epidural analgesia resulted in significantly more normal vaginal deliveries than traditional techniques in an unselected population of nulliparous women. We estimate that almost one in four operative vaginal deliveries could be prevented by the introduction of low-dose epidural analgesia. Although our study was not designed to compare the two low-dose techniques, we believe that both would have the same preventive effect. Caesarean section rates between traditional and low-dose
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