[Maternal and neonatal plasma concentrations of bupivacaine during peridural anesthesia for cesarean section]

Many anesthesiologists prefer epidural anesthesia for cesarean section because of the potential risks of general anesthesia such as Mendelson's syndrome. For this indication, the local anesthetic of first choice is the long-acting substance bupivacaine. The aim of the following study was to determine maternal and neonatal plasma concentrations of bupivacaine 0.5% following epidural anesthesia for cesarean section in order to give critical statements about the systemic toxicity of the local anesthetic. MATERIALS and METHODS. Central venous blood samples were collected for bupivacaine analysis (gas chromatography) in 15 patients (Table 1) undergoing cesarean section with epidural anesthesia over a period of 60 min after injection of 14 to 23 ml bupivacaine 0.5%. Six of these patients had received the epidural anesthesia earlier to relieve labor pain. Before administering the anesthetic dose, a blood sample was taken to determine the baseline value. Immediately after cord clamping, blood sampling was done to determine bupivacaine concentrations in the umbilical artery and vein. Apgar scores and blood gases were also checked and compared with those of neonates born by cesarean section under general anesthesia. RESULTS. Ten to 15 min following epidural application of 70 to 115 mg bupivacaine (mean = 99 mg), peak plasma concentrations occurred (mean = 0.41 micrograms/ml) The maximum plasma level of 0.7 micrograms/ml bupivacaine was found in a patient who had received epidural anesthesia for pain relief during labor. In this case, the baseline bupivacaine level after several epidural injections (125 mg in 15 h) before the anesthetic dose for cesarean section was 0.2 micrograms/ml. Immediately after delivery the mean plasma bupivacaine concentrations in the umbilical vein and artery were 0.11 micrograms/ml and 0.07 micrograms/ml respectively. Apgar scores and blood gas analyses showed no significant difference between neonates born by cesarean section under regional or general anesthesia. DISCUSSION. Using bupivacaine 0.5% for epidural anesthesia for cesarean section, we found maternal and neonatal plasma concentrations of the local anesthetic far below the accepted threshold level for producing systemic toxic reactions. In contrast to others, we obtained good analgesia and sufficient motor blockade accompanied by low plasma levels. In our opinion, there is no need to use 0.75% bupivacaine, especially since peak plasma concentrations of more than 2 micrograms/ml occur shortly after its epidural administration.