• Jens Børglum, Kenneth Jensen, Anders F Christensen, Lotte C G Hoegberg, Sys S Johansen, P-A Lönnqvist, and Tejs Jansen.
• Department of Anesthesia and Intensive Care Medicine, Copenhagen University Hospital: Bispebjerg, Bispebjerg Bakke 23, DK-2400 Copenhagen NV, Denmark. jens.borglum@gmail.com
• Reg Anesth Pain Med. 2012 May 1;37(3):294-301.

Background And ObjectivesThe ability of transversus abdominis plane (TAP) blocks to anesthetize the upper abdomen remains debatable. We aimed to describe the local anesthetic distribution following ultrasound-guided TAP blocks with repeated magnetic resonance imaging investigations and to relate this to the resulting dermatomal anesthesia.MethodsEight volunteers were included in a randomized, observer-blinded study. Sixty milliliters of ropivacaine 0.375% was administered: 1 injection of 30 mL as a lateral classic TAP block, followed by a sham upper intercostal TAP block, and on the contralateral side, 2 separate 15-mL injections at the upper intercostal and lateral classic TAP plexuses, respectively. The primary outcome measure was magnetic resonance imaging-assessed area expansion of all injectates over a 6-hr period. Dermatomal anesthesia and sequential serum ropivacaine levels were recorded at the same time intervals.ResultsAll injectate areas expanded in a statistically significant manner in the anterior abdominal wall. Lateral classic TAP blocks with 30-mL injectates did not extend into the upper intercostal TAP plexus. The dual 15-mL injectates on the other hemiabdomen remained within the upper intercostal and lateral classic TAP compartments and resulted in significantly (P < 0.018) more widespread dermatomal anesthesia. Measured serum ropivacaine concentrations were below the potential level of toxicity.ConclusionsMagnetic resonance imaging analysis revealed a significant time-dependent expansion of injectates. Magnetic resonance imaging and the degree of dermatomal anesthesia confirmed that the upper and lateral TAP compartments do not appear to communicate. Separate injections at the upper intercostal and lateral classic TAP plexuses are necessary to block the entire abdominal wall.

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