Ultrasound-guided lateral and subcostal transversus abdominis plane block in calves: a cadaveric study

To describe and assess the ultrasound-guided transversus abdominis plane (TAP) block feasibility in calf cadavers, to compare two injection volumes and to evaluate possible undesired solution spreads.

Prospective, descriptive, anatomic study.

A group of 15 bovine cadavers weighing 47±11 kg (mean±standard deviation).

Lateral (n = 24) and subcostal (n = 12) TAP block approaches were assessed. For each approach, two volumes (0.2 or 0.4 mL kg^-1) of toluidine blue and contrast medium were injected using both sides of the animals. Nerve staining was assessed by anatomical dissection and spread of injectate by contrast-enhanced computed tomography. Objective and subjective technique feasibility was evaluated by a specific score (poor, good, excellent).

Using the lateral approach, 58%, 92% and 25% and 75%, 83% and 25% of the thirteenth thoracic, first and second lumbar nerves were stained by 0.2 and 0.4 mL kg^-1, respectively. Craniocaudal and dorsoventral solution spread and number of blocks that adequately stained an individual nerve were not significantly different between the volumes. Using the subcostal approach, 67%, 83%, 67%, 67% and 50%, and 83%, 100%, 83%, 83% and 50% of the eighth, ninth, tenth, eleventh, twelfth thoracic nerves were stained by 0.2 and 0.4 mL kg^-1, respectively. With both techniques, no intraspinal and one intraperitoneal spread were observed. Objective and subjective feasibility score was excellent for both approaches in the majority of the cases.

TAP injections were easy to perform with both techniques in calf cadavers. The volume of injectate did not influence spread. The authors conclude that a combination of the two approaches is necessary, but perhaps not sufficient, to stain all of the nerves innervating the ventral abdominal wall. Further studies are required to refine the technique and evaluate its efficacy in preventing nociception in calves.