Elective induction of labor conducted under lumbar epidural block. II. Labor induction by amniotomy and intravenous prostaglandin.

Labor was electively induced at term in 117 clinically normal nulliparae and parous women by combining low amniotomy with intravenous administration of prostaglandin F2 alpha (n = 64) or prostaglandin E2 (n = 53). Analgesia was obtained by continuous lumbar epidural block with bupivacaine. The procedure was very effective in producing vaginal delivery within 24 h after prostaglandin infusion (n = 115), but it was accompanied by an extremely high incidence of uterine hypertonus. Tentative explanations for the transient uterine hyperstimulation are a direct stimulatory effect of the local anesthetic on the contractility of the myometrial fiber and/or a temporarily higher amount of circulating oxytocic compound reaching the myometrium due to local vasodilatation as a result of sympathetic nerve blockade. In some cases uterine hypertonus was associated with slowing of the basal fetal heart rate and, when severe, with the appearance of late deceleration patterns and fetal acidosis. In other cases the fetal heart rate deceleration is explained by the toxic effect of bupivacaine on the myocard. Since both the myometrial hyperactivity and the FHR alterations were temporary, fetal biochemical parameters were unaffected at completion of the first stage of labor. Because with intravenous prostaglandin uterine hyperstimulation is more difficult to avoid and regional analgesia further increases the hazard of both hypertonus and fetal heart rate deceleration, the combined application of an intravenous prostaglandin and continuous epidural analgesia should not be introduced into obstetrical practice.