A comparison of motor block between ropivacaine and bupivacaine for continuous labor epidural analgesia.

The aim of the present study was to compare the amount of motor block produced by different loading doses of ropivacaine and bupivacaine when delivered in a dilute solution with added opioid. Sixty-eight healthy term primigravid parturients were randomized to receive an initial bolus dose of 10 mL of 1 of the following: 0.25% bupivacaine (high bupivacaine), 0.25% ropivacaine (high ropivacaine), 0.125% bupivacaine (low bupivacaine), or 0.125% ropivacaine (low ropivacaine). Each loading dose had 10 micrograms of sufentanil added to it. All groups received a continuous infusion of a 0.1% study drug infusion with 0.6 microgram/mL of sufentanil at a rate of 8 to 14 mL/h to maintain analgesia. Supplemental doses of 10 mL of a 0.125% study solution with 10 micrograms of sufentanil were given as needed. Pain scores and a modified Bromage scale were used to assess analgesia and motor block. A statistically significant greater percentage of parturients receiving bupivacaine had motor block than those who received ropivacaine, with a marked decrease in the occurrence of motor block in the low ropivacaine group. The pain relief seemed to be less satisfactory in the ropivacaine groups, but the difference was not statistically significant. Ropivacaine produced significantly less motor block than bupivacaine in the 0.25% and the 0.125% loading doses, with the greatest difference seen in the lower concentration loading dose of ropivacaine.