Ultrasound-guided transversus abdominis plane injection with computed tomography correlation: a cadaveric study

BACKGROUND Ultrasound-guided transversus abdominis plane (TAP) injections are increasingly being used as an alternative to traditional perioperative analgesia in the abdominal region. With the use of a "blind" TAP block technique, these procedures have had variable success in cadaver and in vivo studies. For more accurate injection with the intended medication, ultrasound guidance allows visualization of the correct layer of the abdominal wall planes in which the thoracolumbar nerves reside. OBJECTIVE To assess the spread of various volumes of contrast placed under live ultrasound guidance into the TAP using computed tomography (CT). METHODS Four TAP blocks were performed on 2 fresh frozen cadaver torsos with predetermined contrast volumes of 5, 10, 15, or 20 mL. A CT scan of the cadaver was then performed and interpreted by a musculoskeletal radiologist. This cadaver study was carried out at a tertiary care academic medical center. RESULTS Cranial-caudal spread of injected contrast correlated with increasing injectate volume and was roughly 1 vertebral level (end plate to end plate) for the 5 mL injection and 2 vertebral levels for the 10, 15, and 20 mL injections. However, the degree of injectate spread may be different for live patients than for cadavers. CONCLUSION This study helps further the understanding of injectate spread following ultrasound-guided TAP injections. Specifically, it suggests that 15 mL provides additional cranial-caudal spread and may be an optimal volume of anesthesia.