Predicting plasma concentrations of bupivacaine after epidural administration in obstetric analgesia.

The elimination half-life and plasma concentrations of bupivacaine were predicted after its epidural administration in six pregnant women at term for elective Caesarean section using a repeated one-point method. There was a direct correlation between predicted concentrations and observed concentrations of bupivacaine using this simple method (r = 0.9947). The assay of bupivacaine in a 0.5-ml plasma by gas chromatography with nitrogen sensitive detection can be achieved in a short time (rapid extraction and chromatographic analysis required 20 min and 10 min, respectively) to cope with emergency. It is suggested that the repeated one-point method may be useful to obtain early prediction of kinetic parameters in patients who required prolonged epidural anesthesia with bupivacaine in order to minimize adverse effects.