An Image Study on Local Anesthetic Spread in Healthy Volunteers Receiving Subcostal Exterior Semilunaris Transversus Abdominis Plane (SE-TAP) Block

BACKGROUND: Despite the popularity of the ultrasound-guided transversus abdominis plane (TAP) block and the diversity of advancing approaches, the extent of injectate spread limits its clinical benefits. This study used three-dimensional computed tomography (3D-CT) imaging and a cold stimulus to evaluate the spread of a local anesthetic injected through the subcostal exterior semilunaris to transversus abdominis plane (SE-TAP) block in healthy volunteers. METHODS: Eight healthy volunteers received a right-side ultrasound-guided SE-TAP block with 25 mL of 0.3% ropivacaine. The sensory block was assessed by a cold stimulus at 30 min, 2 h, 4 h, and 8 h following the SE-TAP block according to the 18-zone division method. A CT scan and 3D imaging were performed after the first sensory assessment. RESULTS: The injectate spread into the transversus abdominis space in all eight volunteers. 3D imaging confirmed that the injectate spread extensively along the costal margin in the plane of the transverse abdominis muscle and that it surpassed the semilunaris. Regarding the assessment using cold stimulus, five of six anterior zones and three of six lateral zones obtained successful rates of cutaneous sensory block higher than 75% 30 min after SE-TAP. Sensory block was achieved in the ventral dermatomes of all volunteers. CONCLUSION: Our study showed that the SE-TAP injectate, which was administered using simple anatomical landmarks to provide reliable analgesia for abdominal surgery, consistently spread along the costal margin and extensively blocked cutaneous sensitivity in the anterior and lateral abdominal walls.