Epidural clonidine after cesarean section. Appropriate dose and effect of prior local anesthetic.

Epidurally administered clonidine represents a new approach to postcesarean section pain therapy, yet the appropriate bolus dose and infusion to provide effective pain relief have not been defined. In addition, whether 2-chloroprocaine, a commonly used local anesthetic for intraoperative anesthesia, interferes with clonidine's analgesia, as it does with that of opioids, has not been examined. In this study, using a randomized, blinded design, 63 women received either bupivacaine or 2-chloroprocaine for epidural anesthesia for cesarean section and then received, upon request for analgesia in the recovery room, epidural clonidine 400 micrograms or 800 micrograms bolus, each followed by a 24-h infusion of 40 micrograms/h, or an equivalent volume bolus and infusion of saline. In the bupivacaine group, both clonidine doses produced equivalent analgesia, as determined by pain scores and time to first supplemental intravenous morphine request, and sustained analgesia was produced by clonidine infusion, as measured by need for supplemental morphine. In contrast, 2-chloroprocaine diminished analgesia from 800 micrograms by 21% and abolished analgesia from 400 micrograms clonidine. After 2-chloroprocaine, sustained analgesia from continuous clonidine infusion was present only in the group who had received 800 micrograms clonidine. Clonidine did not alter resolution of residual local anesthetic sensory blockade, as measured by 2- or 4-segment regression following either local anesthetic, but did prolong duration of motor blockade in women receiving bupivacaine. Clonidine produced small decreases in heart rate and blood pressure. One patient received iv fluids for hypotension; one had asymptomatic bradycardia resolving without therapy; and one had mild hypoxemia with snoring during clonidine-induced sedation, responding to supplemental oxygen.(ABSTRACT TRUNCATED AT 250 WORDS)