Epidural analgesia is the most common and most effective form of pain relief during labor, but it is associated with increased rates of instrumental delivery, prolonged labor, and oxytocin augmentation. Many of these adverse effects are attributed to dense paralysis of motor functions that can affect pelvic muscle tone, mobility, and the ability to push with contractions. New “low-dose” forms of epidural analgesia combine lower doses of local anesthetic with an opioid (fentanyl) to provide pain relief but retain motor function. Women in labor can walk while receiving epidural analgesia and are reported to have lower rates of complications related to motor dysfunction. Shennan and colleagues in the Comparative Obstetric Mobile Epidural Trial study group compared the new techniques to traditional epidural analgesia in two British teaching hospitals.

All women who requested epidural anesthesia were eligible for the study unless there was a contraindication to the procedure or delivery was imminent. Patients were provided with information about epidurals and the study before labor and were given more information when admitted to the delivery unit. More than 1,000 women were randomly assigned to groups using one of three epidural techniques. Traditional epidural was provided to 353 women, low-dose combined spinal epidural to 351, and low-dose infusion epidural to 350. Patient assignment could not be concealed, but the investigators were not involved in any decisions concerning the clinical management of the patients. In addition, the research midwives who interviewed the patients during the follow-up period were not informed of the treatment allocations. Data were collected throughout delivery, by interview 24 to 48 hours after delivery, and by questionnaire one year after delivery. Follow-up was achieved in 99 percent of patients.

The normal vaginal delivery rate was 35 percent in women using traditional epidurals but 43 percent in each of the “low-dose” epidural groups (see accompanying table). The rate of instrumental vaginal delivery was also reduced, from 37 percent with traditional epidural to 28 to 29 percent with low-dose epidural. The rate of cesarean delivery was similar in all three groups, and the indications for cesarean delivery (predominately delay in the second stage of labor and fetal distress) were comparable among the groups. More women in the low-dose groups had second-stage durations of 60 minutes or less than in the traditional epidural group. Women reported good pain relief with all three methods. Women in the low-dose groups retained significant motor function, and one third could walk or stand during labor. Although the number of infants requiring resuscitation and the numbers admitted to special care were similar, low Apgar scores were more common in infants born following low-dose epidural. This effect could have resulted from exposure to fentanyl during labor.

The authors conclude that low-dose techniques have clear and significant advantages over traditional epidural analgesia. They argue that if these results are validated in larger studies and other populations, conventional epidurals will be replaced by low-dose techniques.

editor's note: The authors argue that the new techniques could avoid about one quarter of operative deliveries when epidural analgesia is used. They are enthusiastic about the potential benefits of these new techniques, which appear to be obtained without compromising pain relief. Although measured in the study, patient satisfaction is not reported, nor is the incidence of headache, a common after-effect of epidural analgesia.—a.d.w.