An Anatomical, Sonographic, and Computed Tomography Study of the Transversus Abdominis Plane Block in Cat Cadavers

SIMPLE SUMMARY: The transversus abdominis plane (TAP) block is a locoregional technique used for postoperative analgesia after abdominal surgery, reducing the consumption of systemic analgesic drugs. The aim of this cadaveric study was to evaluate the spread of an anaesthetic-contrast dye solution administered by an ultrasound-guided 1-point (lateral; TAP-L approach) or 2-point (subcostal and lateral; TAP-SL approach) TAP block technique. Contrast distribution was assessed by computed tomography whereas nerve staining was assessed by anatomical dissection. The 2-point-injection technique provided a wider injectate spread within the TAP than the 1-point technique. Further clinical studies are warranted to investigate the analgesic effect of these TAP block approaches in cats undergoing abdominal surgery. ABSTRACT: This study compared the distribution of a bupivacaine–iopamidol–dye solution following ultrasound-guided in-plane TAP injection using a 1-point (TAP-L) or 2-point (TAP-SL) approach in cat cadavers. Two cadavers were used to study the TAP sonoanatomy while eight cadavers were enrolled in a randomized, prospective, blinded investigation. Each cat randomly received a TAP-L with 0.5 mL/kg in one hemiabdomen and a TAP-SL with 0.25 mL/kg/point in the contralateral hemiabdomen. After injection, computed tomography and dissection were performed to assess contrast distribution and number of stained target nerves. TAP-SL resulted in a wider contrast spread (mm) compared with TAP-L (87 ± 7 versus 71 ± 9; p = 0.002). The prevalence of nerve staining was higher using TAP-SL than TAP-L (p = 0.001). The ventral branches of T10, T11, T12, T13, L1 and L2 were stained in 2/8, 2/8, 5/8, 7/8, 4/8 and 1/8, and in 7/8, 7/8, 8/8, 8/8, 8/8 and 1/8 using TAP-L and TAP-SL approaches, respectively. Computed tomography and dissection identified minimal injectate intraperitoneally or within the falciform ligament fat following 1 TAP-L and 2 TAP-SL. Ultrasound-guided TAP-SL provided better injectate distribution around the thoracolumbar spinal nerve branches than TAP-L.