The dose of local anesthetic used in spinal-epidural analgesia for external cephalic version has no influence on the success rate of the procedure, according to a randomized controlled trial. The conclusion contradicts earlier meta-analyses.
Although the trial investigators found dose-dependent changes in some secondary outcomes, they noted that these results highlight the importance of blinding in clinical trials.
“As we all know, the growing cesarean rate presents a major public health challenge in the United States,” said Laurie A. Chalifoux, MD, an instructor in anesthesiology at Northwestern University’s Feinberg School of Medicine, in Chicago. “Breech presentation is the leading cause of primary or repeat cesarean deliveries, and the American College of Obstetrics and Gynecology endorses the use of external cephalic version to move the fetus to the vertex position in hopes of vaginal delivery.
“As we know, anesthesia for external cephalic version has developed from nothing to IV opiate choices to a wide variety of combined spinal-epidural techniques,” she said. “However, optimal dosing of this approach is still widely debated.”
Previous nonrandomized trials and meta-analyses have suggested that higher doses of local anesthetic result in increased external cephalic version success (Obstet Gynecol 2011;118:1137-1144; Int J Obstet Anesth 2009;18:328-334; Can J Anaesth 2010;57:408-414), leading the current research team to hypothesize that an increased intrathecal dose of bupivacaine—as part of a combined spinal-epidural technique—would increase the success rate of external cephalic version, thereby decreasing the cesarean delivery rate.
“This is a unique opportunity for us to work together with our obstetric colleagues to optimize the outcomes of external cephalic version and avoid some of the downstream morbidity and mortality associated with primary and with repeat cesarean deliveries,” Dr. Chalifoux said.
First Randomized Trial
The investigators enrolled 229 women into the trial. The parturients were randomly assigned to receive either 2.5 mg (n=58), 5 mg (n=56), 7.5 mg (n=58) or 10 mg (n=57) of intrathecal bupivacaine—along with 15 mcg fentanyl—prior to the external cephalic version. Various secondary outcomes also were studied, including patient pain scores and overall satisfaction, perceived abdominal relaxation by the obstetrician, hospital length of stay, incidence of complications and hypotension requiring vasopressor treatment. No epidural test dose was used. “Everyone but the anesthesia team was blinded, for safety reasons,” Dr. Chalifoux added.
As reported at the 2016 annual meeting of the American Society of Anesthesiologists (abstract BOC07), there was no difference among groups in either external cephalic version success (P=0.99) or mode of delivery (P=0.70). Similarly, the obstetrician’s perception of abdominal relaxation did not differ significantly between patients in the four groups (P=0.162). Finally, the indication for cesarean delivery (P=0.779) and rates of crash cesarean delivery (one in each group) also were similar among groups.
Although the investigators found a dose-dependent reduction in pain scores with increasing bupivacaine dose, it came at the cost of a higher incidence of hypotension. Similarly, the time to discharge became significantly longer as dose increased (Table).
These results, Dr. Chalifoux noted, are the first of their kind from a randomized controlled trial. “Our negative results contradict previous literature, which did suggest a dose-finding effect,” she said. Equally important, she said, is that the current trial highlights the importance of blinding in clinical trials. “We believe that if the obstetrician is blinded to the group assignment of bupivacaine dose, they’ll give a good, uniform effort, not giving up quickly because it was a low dose or trying extra hard because it was a high dose.”
Furthermore, in previous unblinded studies, patient recruitment and neuraxial dosing may have been influenced by patient factors, obstetrician preference or even the perceived likelihood of successful external cephalic version.
“In conclusion,” she said, “escalating neuraxial local anesthetic dose, with resultant greater block density, does not alter external cephalic version rate or reduce the cesarean delivery rate. However, it does marginally improve pain scores and result in increased hypotension and vasopressor administration, as well as significantly increased length of stay.” Nevertheless, Dr. Chalifoux was also quick to point out that the current study had its own limitations, including the lack of a valid control group and the fact that anesthesiologists were not blinded to the bupivacaine dose.
According to Heather Nixon, MD, associate professor of anesthesiology and head of the Obstetric Anesthesiology Division at the University of Illinois Hospital and Health Science System, in Chicago, the study challenges previous literature regarding the optimal intrathecal dose of local anesthetic needed to facilitate successful external cephalic version by obstetric care providers. “Previously, we believed that higher doses of intrathecal local anesthetics would result in higher [external cephalic version] success rates,” she noted. “The data from this blinded study seem to indicate that success rates are not so reliant on intrathecal dose.
“When caring for obstetric patients, we must always balance the risks and benefits of any procedure,” Dr. Nixon added. “For [external cephalic version] procedures, this means the benefit of possible vaginal delivery versus the risk of hypotension, and the need for emergency cesarean delivery. Traditionally, we thought that providing dense neuraxial blockade might increase the likelihood of patient hypotension and need for emergency delivery. Although the study was not powered to detect differences in rare complications like prolonged fetal bradycardia and placental abruption, the results of Dr. Chalifoux’s study do not support the theory that higher doses of intrathecal local anesthetic significantly increase these complications.
“Similarly, due to the study design that allowed obstetricians to be blinded, there was no control group and so no comparisons can be made regarding complication or success rates when no analgesia or intravenous analgesia is provided.” The optimum dose, she said, may well be intermediate doses, although further studies are needed to confirm this.