Effects of adding epinephrine on the early systemic absorption kinetics of local anesthetics in abdominal truncal blocks

We evaluated the pharmacokinetics of ropivacaine following rectus sheath block (RSB) and transversus abdominis plane (TAP) block with or without epinephrine. A total of 26 adult patients undergoing lower abdominal surgery with RSB (=RSB trial) and another 26 adult patients undergoing open prostatectomy with TAP block (=TAP trial) were enrolled. Patients were randomly assigned to receive either a mixture of 0.75 % ropivacaine 13.2 mL with 1 % plain lidocaine 6.8 mL (TAP-E(−) and RSB-E(−) groups) or a mixture of 0.75 % ropivacaine 13.2 mL and 1 % lidocaine containing adrenaline (1:100,000) 6.8 mL (TAP-E(+) and RSB-E(+) groups) under general anesthesia. The serum concentrations of ropivacaine were measured using gas chromatography with mass spectrometry. The peak concentration was significantly lower and time to peak concentration was significantly longer in the TAP-E(+) group than in the TAP-E(−) group (P < 0.05 and <0.01, respectively), while there were no significant differences in these parameters between the RSB-E(+) and RSB-E(−) groups. These results indicate that epinephrine attenuates the early phase of local anesthetic absorption from the injected site in TAP blocks, but not RSB.