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A randomized double-blinded trial of the effects of bupivacaine-induced motor blockade during the second stage of labor
Abstract Number: GM 2
Abstract Type: Original Research
Introduction: The purpose of this study is to examine the effects of bupivacaine on the length of the second stage of labor in nulliparous women. Specifically, we sought to answer the question of whether or not bupivacaine lengthened the second stage. Many researchers believe that the bupivacaine-induced motor blockade is the etiology of the lengthened labor patterns in women receiving epidural analgesia. Our study's primary outcome was the difference in duration of the second stage in women having epidural bupivacaine versus epidural fentanyl alone. And finally, prior studies in our institution have shown an increase of operative vaginal delivery in women with epidurals, and it was hypothesized that this increase was secondary to the motor blockade caused by epidural bupivacaine. Our current study probed this question by looking at the obstetrical outcomes in women who had epidural bupivacaine versus those who had epidural fentanyl alone.
Methods: 310 nulliparous women with labor epidurals undergoing induction of labor at Parkland Hospital were randomized at 8 cm cervical dilation to receive either: 0.125% bupivacaine with 2 mcg fentanyl/cc at 10 cc/hr, or fentanyl 10 mcg/cc at 10 cc/hr in a double-blinded randomized fashion. Break-through pain was treated with PCEA boluses of the patient's randomized epidural solution, and either group could receive nurse-administered meperidine boluses per protocol. Bromage scores, VAS scores, and incidence of pruritus were ascertained at baseline and at regular intervals. Obstetrical and neonatal outcome were recorded.
Results: Patient demographics were similar in both groups, and there was no difference in maternal co-morbidities. There was no difference in the mode of delivery. 73% in the bupivacaine group delivered via SVD versus 81% in the fentanyl-only group (P 0.09). The operative vaginal delivery rate was 12% in the bupivacaine group versus 8% in the fentanyl-only group (P 0.17). The cesarean section rate was 15% in the bupivacaine group and 12% in the fentanyl-only group (P 0.38). The mean duration of the second stage was 93 minutes in the bupivacaine group versus 83 minutes in the fentanyl-only group (P 0.17). There was no statistical difference in the VAS scores between the two groups, with an average VAS score of 2/10. There was a statistically significant difference in the Bromage scores, with the fentanyl-only group having more motor function (5/6 on the Bromage scale) up to 60 minutes after randomization (P 0.03). There was no difference in low Apgar scores, admission to NICU, or naloxone administration.
Discussion: While epidural bupivacaine does cause motor blockade in laboring women, the duration of the second stage of labor was not lengthened. Neither obstetric nor neonatal outcomes were different in women who received epidural bupivacaine during the second stage from those who did not. Patient satisfaction was high overall (84-88%), irrespective of randomization.