Epidural analgesia has been associated with slower rates of cervical dilatation, longer labor and more frequent use of oxytocin augmentation, with increased rates of operative delivery. The American College of Obstericians and Gynecologists defines prolonged second stage of labor differently if epidural analgesia is used. Alexander and associates measured the effects of epidural analgesia compared with boluses of meperidine, using the same cohort from a previous similar trial.
Results of the previous study by this group were challenged because of the multiplicity of confounding variables such as parity, use of oxytocin and self-selection of the method of analgesia. These variables were minimized in the current trial. All of the 199 patients in the study were managed on a low-risk unit and delivered spontaneously at term. All of the women were nulliparous and received oxytocin for labor augmentation before the initiation of analgesia. Epidural analgesia was administered in 126 of the women; 73 women received bolus doses of meperidine. The two analgesia groups had the same cervical dilatation on admission (3.3 cm) and at the time of analgesia (4.1 cm), indicating similar progress of labor before oxytocin was initiated. All of the study subjects started at the same juncture of labor, were managed similarly and ended with the same method of delivery. However, the active phase of labor, the duration of the second stage and the admission-to-delivery intervals were all significantly prolonged in women who received epidural analgesia compared with those who received meperidine.
The pelvic examination at the time of epidural administration in the epidural group indicated that cervical dilatation was less than in patients at the time of oxytocin administration. Cervical dilatation was significantly more advanced in the epidural group before oxytocin augmentation than in the meperidine group. However, women with epidural analgesia received oxytocin for longer intervals and required more oxytocin to achieve each centimeter of cervical dilatation. All infants were live-born, and no deaths occurred during the neonatal period in either study group. Apgar scores, umbilical cord blood pH measurements and admission to the intensive care unit did not differ between the two analgesia groups.
Results demonstrated that uterine performance was reduced by epidural analgesia. This was reflected in the longer first and second stages of labor and an increased oxytocin requirement per centimeter of cervical dilatation. Although this study included women who self-selected their methods of analgesia, the analysis after removing these patients did not affect the results. Controlling for other variables known to be related to labor progression, such as parity, progress of labor up to administration of analgesia, oxytocin use and surgical intervention in labor, still demonstrated that epidural analgesia diminishes uterine performance and slows the progress of labor.
The authors conclude that the expectation of labor duration and rate of cervical dilatation should be modified when epidural analgesia is used. They indicate that perhaps when epidural analgesia is used, guidelines for management of the first stage of labor should be modified as they already have been for the second stage of labor. Modifying labor expectations as such may help to reduce the excessive rate of cesarean delivery associated with epidural analgesia.
editor's note: Although epidural analgesia is associated with a longer duration of labor, increased use of oxytocin and increased dystocia, patient satisfaction is high because of the significant reduction in pain after epidural analgesia administration. Given the recent criticism that epidural analgesia increases the rate of operative delivery, it may be that readjusting our expectations for labor progress will allow more women to deliver vaginally with less pain.—b.a.