FETOMATERNAL DISTRIBUTION OF ROPIVACAINE AND BUPIVACAINE AFTER EPIDURAL ADMINISTRATION FOR CESAREAN-SECTION

Ropivacaine is a new amino amide local anesthetic less lipophilic and with a lower affinity for plasma proteins than bupivacaine. The purpos e of this study was to examine the feto-maternal distribution of ropiv acaine and bupivacaine after epidural administration for cesarean sect ion. Healthy parturients were randomly allocated in a double-blinded m anner to receive either 0.5% ropivacaine or 0.5% bupivacaine through a lumbar epidural catheter. The total and free concentrations of ropiva caine and bupivacaine were determined in the maternal and umbilical pl asma. The total dose (mg/kg) required for adequate surgical anesthesia and the resulting maximum total concentrations did not differ signifi cantly between ropivacaine and bupivacaine. The free plasma clearance of bupivacaine was higher than that of ropivacaine (7382 vs 3344 ml/mi n, P=0.0001). The apparent terminal elimination half-life of ropivacai ne was shorter than that of bupivacaine (6.0 vs 8.8 h, P=0.007). At de livery the maternal free plasma concentration of ropivacaine was more than twice that of the free concentration of bupivacaine (0.072 vs 0.0 32 mu g/ml, P=0.002). The free concentration of ropivacaine was about twice that of bupivacaine in the umbilical venous (0.06 vs 0.03 mu g/m l, P=0.001) and umbilical arterial (0.05 vs 0.02 mu g/ml, P=0.007) pla sma. The more rapid plasma clearance of bupivacaine compared to ropiva caine, leading to lower maternal plasma concentrations and hence to lo wer umbilical concentrations at delivery, could be explained by the hi gher lipid solubility, hence greater distribution volume, of bupivacai ne.