Pharmacokinetics of the local anesthetic ropivacaine after transversus abdominis plane block in healthy volunteers

The transversus abdominis plane (TAP) block is a regional anesthetic technique used for pain control following abdominal surgical procedures. While a minimum of systemic side effects is usually expected after local anesthesia, it is unknown to which extent systemic absorption and redistribution to the abdominal wall contributes to the effects of anesthetics. The aim of this study was to determine concentration-time profiles of ropivacaine after the injection of 150 mg of ropivacaine into the lateral abdominal wall in various compartments. The microdialysis technique was used to measure ropivacaine in plasma as well as at abdominal wall sites cranial from the injection site (below the 12th rip) and caudal from the injection site (cranial from the iliac crest) and in the skeletal muscle tissue of the contra lateral thigh of eight healthy volunteers. The mean exposure to ropivacaine measured as the area under the concentration-time curve was significantly higher at the two abdominal sites (240.9 +/- 409.1 and 86.18 +/- 133.50 mu g h/mL, respectively) than in plasma (5.1 +/- 1.0 mu g h/mL) or in peripheral tissue (1.1 +/- 1.2 mu g h/mL). While the high mean concentrations of ropivacaine measured at the abdominal wall sites support the topical concept of the TAP block, the observed variability was striking. While the systemic pharmacokinetics was comparable between subjects, the local distribution of ropivacaine was highly variable after TAP block.