Descriptive study of the innervation of the abdominal wall and degree of nerve staining after transversus abdominis plane block in pig cadavers

Abstract Objective To develop an ultrasound (US) guided transversus abdominis plane (TAP) block in pigs. Study design Prospective, descriptive, experimental study. Animals A total of 26 hemiabdomens belonging to 13 Seghers Hybrid cadavers. Methods The study consisted of two parts. In part one, a preliminary anatomical understanding of the abdominal wall innervation in pigs was established (two hemi-abdomens of one pig). Part two, was divided into three phases, an US guided TAP technique using methylene blue dye (0.3 mL kg-1 for each hemi-abdomen) was developed. In chronological order, a pilot study (phase I) was conducted to establish good injection points (four hemi-abdomens). In phase II a two-point injection technique (10 hemi-abdomens) was performed. A cranial injection was made at 2/3 of the distance between the xyphoid process and the iliac crest, immediately ventral to the rib arch. A caudal injection was performed ventral to the last rib. In phase III a three-point injection technique was performed (10 hemi-abdomens) with an extra injection point halfway between the cranial and caudal injection point. Staining of the different nerves was recorded during dissection. Results In part 1 the nerves innervating the pig’s abdominal wall (thoracic vertebrae 12-16 (T12-16) and lumbar vertebrae 1-3 (L1-3) were identified. In part 2, data from the pilot study, adequate nerve staining with the two-point or three-point injection technique was obtained in T12 (29 versus 45% respectively), T13 (29 versus 100%), T14 (73 versus 45%), T15 (75 versus 78%), T16 (58 versus 78%), L1 (100 versus 75%), L2 (88 versus 84%), L3 (23 versus 0%). Conclusions US guided TAP block can be used in swine but only a moderate success rate for adequate nerve staining was achieved in this study. Further studies are necessary to determine a correct injection volume and assess clinical intra- and postoperative efficacy.